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path: root/sys-kernel/boest-v4.4.196/0020-block-bfq-turn-BFQ-v7r11-for-4.7.0-into-BFQ-v8r3-for.patch
blob: 78b1a12a3dcdbae18bd5c297c96de6c8c184691b (plain) (blame)
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From 34590e77cbd5f7afdb226e5377032ac4b7369625 Mon Sep 17 00:00:00 2001
From: Paolo Valente <paolo.valente@linaro.org>
Date: Tue, 17 May 2016 08:28:04 +0200
Subject: [PATCH 20/20] block, bfq: turn BFQ-v7r11 for 4.7.0 into BFQ-v8r3 for
 4.7.0

---
 block/Kconfig.iosched |    2 +-
 block/bfq-cgroup.c    |  498 ++++----
 block/bfq-iosched.c   | 2582 ++++++++++++++++++++++++-----------------
 block/bfq-sched.c     |  441 +++++--
 block/bfq.h           |  706 ++++++-----
 5 files changed, 2482 insertions(+), 1747 deletions(-)

diff --git a/block/Kconfig.iosched b/block/Kconfig.iosched
index f78cd1a9fc1b..6d9257924ddf 100644
--- a/block/Kconfig.iosched
+++ b/block/Kconfig.iosched
@@ -53,7 +53,7 @@ config IOSCHED_BFQ

 
 config BFQ_GROUP_IOSCHED
 	bool "BFQ hierarchical scheduling support"
-	depends on CGROUPS && IOSCHED_BFQ=y
+	depends on IOSCHED_BFQ && BLK_CGROUP
 	default n
 	---help---
 	  Enable hierarchical scheduling in BFQ, using the blkio controller.
diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index 5ee99ecbd91a..c83d90c99f50 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -162,7 +162,6 @@ static struct blkcg_gq *bfqg_to_blkg(struct bfq_group *bfqg)
 static struct bfq_group *blkg_to_bfqg(struct blkcg_gq *blkg)
 {
 	struct blkg_policy_data *pd = blkg_to_pd(blkg, &blkcg_policy_bfq);
-	BUG_ON(!pd);
 	return pd_to_bfqg(pd);
 }
 
@@ -224,14 +223,6 @@ static void bfqg_stats_update_io_merged(struct bfq_group *bfqg, int rw)
 	blkg_rwstat_add(&bfqg->stats.merged, rw, 1);
 }
 }
 
-static void bfqg_stats_update_dispatch(struct bfq_group *bfqg,
-					      uint64_t bytes, int rw)
-{
-	blkg_stat_add(&bfqg->stats.sectors, bytes >> 9);
-	blkg_rwstat_add(&bfqg->stats.serviced, rw, 1);
-	blkg_rwstat_add(&bfqg->stats.service_bytes, rw, bytes);
-}
-
 static void bfqg_stats_update_completion(struct bfq_group *bfqg,
 			uint64_t start_time, uint64_t io_start_time, int rw)
 {
@@ -248,17 +239,11 @@ static void bfqg_stats_update_completion(struct bfq_group *bfqg,
 /* @stats = 0 */
 static void bfqg_stats_reset(struct bfqg_stats *stats)
 {
-	if (!stats)
-		return;
-
 	/* queued stats shouldn't be cleared */
-	blkg_rwstat_reset(&stats->service_bytes);
-	blkg_rwstat_reset(&stats->serviced);
 	blkg_rwstat_reset(&stats->merged);
 	blkg_rwstat_reset(&stats->service_time);
 	blkg_rwstat_reset(&stats->wait_time);
 	blkg_stat_reset(&stats->time);
-	blkg_stat_reset(&stats->unaccounted_time);
 	blkg_stat_reset(&stats->avg_queue_size_sum);
 	blkg_stat_reset(&stats->avg_queue_size_samples);
 	blkg_stat_reset(&stats->dequeue);
@@ -268,21 +253,19 @@ static void bfqg_stats_reset(struct bfqg_stats *stats)
 }
 }
 
 /* @to += @from */
-static void bfqg_stats_merge(struct bfqg_stats *to, struct bfqg_stats *from)
+static void bfqg_stats_add_aux(struct bfqg_stats *to, struct bfqg_stats *from)
 {
 	if (!to || !from)
 		return;
 
 	/* queued stats shouldn't be cleared */
-	blkg_rwstat_add_aux(&to->service_bytes, &from->service_bytes);
-	blkg_rwstat_add_aux(&to->serviced, &from->serviced);
 	blkg_rwstat_add_aux(&to->merged, &from->merged);
 	blkg_rwstat_add_aux(&to->service_time, &from->service_time);
 	blkg_rwstat_add_aux(&to->wait_time, &from->wait_time);
 	blkg_stat_add_aux(&from->time, &from->time);
-	blkg_stat_add_aux(&to->unaccounted_time, &from->unaccounted_time);
 	blkg_stat_add_aux(&to->avg_queue_size_sum, &from->avg_queue_size_sum);
-	blkg_stat_add_aux(&to->avg_queue_size_samples, &from->avg_queue_size_samples);
+	blkg_stat_add_aux(&to->avg_queue_size_samples,
+			  &from->avg_queue_size_samples);
 	blkg_stat_add_aux(&to->dequeue, &from->dequeue);
 	blkg_stat_add_aux(&to->group_wait_time, &from->group_wait_time);
 	blkg_stat_add_aux(&to->idle_time, &from->idle_time);
@@ -308,10 +291,8 @@ static void bfqg_stats_xfer_dead(struct bfq_group *bfqg)
 	if (unlikely(!parent))
 		return;
 
-	bfqg_stats_merge(&parent->dead_stats, &bfqg->stats);
-	bfqg_stats_merge(&parent->dead_stats, &bfqg->dead_stats);
+	bfqg_stats_add_aux(&parent->stats, &bfqg->stats);
 	bfqg_stats_reset(&bfqg->stats);
-	bfqg_stats_reset(&bfqg->dead_stats);
 }

 
 static void bfq_init_entity(struct bfq_entity *entity,
@@ -332,15 +313,11 @@ static void bfq_init_entity(struct bfq_entity *entity,

 
 static void bfqg_stats_exit(struct bfqg_stats *stats)
 {
-	blkg_rwstat_exit(&stats->service_bytes);
-	blkg_rwstat_exit(&stats->serviced);
 	blkg_rwstat_exit(&stats->merged);
 	blkg_rwstat_exit(&stats->service_time);
 	blkg_rwstat_exit(&stats->wait_time);
 	blkg_rwstat_exit(&stats->queued);
-	blkg_stat_exit(&stats->sectors);
 	blkg_stat_exit(&stats->time);
-	blkg_stat_exit(&stats->unaccounted_time);
 	blkg_stat_exit(&stats->avg_queue_size_sum);
 	blkg_stat_exit(&stats->avg_queue_size_samples);
 	blkg_stat_exit(&stats->dequeue);
@@ -351,15 +328,11 @@ static void bfqg_stats_exit(struct bfqg_stats *stats)

 
 static int bfqg_stats_init(struct bfqg_stats *stats, gfp_t gfp)
 {
 {
-	if (blkg_rwstat_init(&stats->service_bytes, gfp) ||
-	    blkg_rwstat_init(&stats->serviced, gfp) ||
-	    blkg_rwstat_init(&stats->merged, gfp) ||
+	if (blkg_rwstat_init(&stats->merged, gfp) ||
 	    blkg_rwstat_init(&stats->service_time, gfp) ||
 	    blkg_rwstat_init(&stats->wait_time, gfp) ||
 	    blkg_rwstat_init(&stats->queued, gfp) ||
-	    blkg_stat_init(&stats->sectors, gfp) ||
 	    blkg_stat_init(&stats->time, gfp) ||
-	    blkg_stat_init(&stats->unaccounted_time, gfp) ||
 	    blkg_stat_init(&stats->avg_queue_size_sum, gfp) ||
 	    blkg_stat_init(&stats->avg_queue_size_samples, gfp) ||
 	    blkg_stat_init(&stats->dequeue, gfp) ||
@@ -374,20 +347,36 @@ static int bfqg_stats_init(struct bfqg_stats *stats, gfp_t gfp)
 }

 
 static struct bfq_group_data *cpd_to_bfqgd(struct blkcg_policy_data *cpd)
- {
+{
 	return cpd ? container_of(cpd, struct bfq_group_data, pd) : NULL;
- }
+}
 
 static struct bfq_group_data *blkcg_to_bfqgd(struct blkcg *blkcg)
 {
 	return cpd_to_bfqgd(blkcg_to_cpd(blkcg, &blkcg_policy_bfq));
 }

 
+static struct blkcg_policy_data *bfq_cpd_alloc(gfp_t gfp)
+{
+	struct bfq_group_data *bgd;
+
+	bgd = kzalloc(sizeof(*bgd), GFP_KERNEL);
+	if (!bgd)
+		return NULL;
+	return &bgd->pd;
+}
+
 static void bfq_cpd_init(struct blkcg_policy_data *cpd)
 {
 {
 	struct bfq_group_data *d = cpd_to_bfqgd(cpd);
 
-	d->weight = BFQ_DEFAULT_GRP_WEIGHT;
+	d->weight = cgroup_subsys_on_dfl(io_cgrp_subsys) ?
+		CGROUP_WEIGHT_DFL : BFQ_WEIGHT_LEGACY_DFL;
+}
+
+static void bfq_cpd_free(struct blkcg_policy_data *cpd)
+{
+	kfree(cpd_to_bfqgd(cpd));
 }

 
 static struct blkg_policy_data *bfq_pd_alloc(gfp_t gfp, int node)
@@ -398,8 +387,7 @@ static struct blkg_policy_data *bfq_pd_alloc(gfp_t gfp, int node)
 	if (!bfqg)
 		return NULL;
 
-	if (bfqg_stats_init(&bfqg->stats, gfp) ||
-	    bfqg_stats_init(&bfqg->dead_stats, gfp)) {
+	if (bfqg_stats_init(&bfqg->stats, gfp)) {
 		kfree(bfqg);
 		return NULL;
 	}
@@ -407,27 +395,20 @@ static struct blkg_policy_data *bfq_pd_alloc(gfp_t gfp, int node)
 	return &bfqg->pd;
 }

 
-static void bfq_group_set_parent(struct bfq_group *bfqg,
-					struct bfq_group *parent)
-{
-	struct bfq_entity *entity;
-
-	BUG_ON(!parent);
-	BUG_ON(!bfqg);
-	BUG_ON(bfqg == parent);
-
-	entity = &bfqg->entity;
-	entity->parent = parent->my_entity;
-	entity->sched_data = &parent->sched_data;
-}
-
 static void bfq_pd_init(struct blkg_policy_data *pd)
 {
-	struct blkcg_gq *blkg = pd_to_blkg(pd);
-	struct bfq_group *bfqg = blkg_to_bfqg(blkg);
-	struct bfq_data *bfqd = blkg->q->elevator->elevator_data;
-	struct bfq_entity *entity = &bfqg->entity;
-	struct bfq_group_data *d = blkcg_to_bfqgd(blkg->blkcg);
+	struct blkcg_gq *blkg;
+	struct bfq_group *bfqg;
+	struct bfq_data *bfqd;
+	struct bfq_entity *entity;
+	struct bfq_group_data *d;
+
+	blkg = pd_to_blkg(pd);
+	BUG_ON(!blkg);
+	bfqg = blkg_to_bfqg(blkg);
+	bfqd = blkg->q->elevator->elevator_data;
+	entity = &bfqg->entity;
+	d = blkcg_to_bfqgd(blkg->blkcg);
 
 	entity->orig_weight = entity->weight = entity->new_weight = d->weight;
 	entity->my_sched_data = &bfqg->sched_data;
@@ -445,70 +426,53 @@ static void bfq_pd_free(struct blkg_policy_data *pd)
 	struct bfq_group *bfqg = pd_to_bfqg(pd);

 
 	bfqg_stats_exit(&bfqg->stats);
-	bfqg_stats_exit(&bfqg->dead_stats);
-
 	return kfree(bfqg);
 }
 
-/* offset delta from bfqg->stats to bfqg->dead_stats */
-static const int dead_stats_off_delta = offsetof(struct bfq_group, dead_stats) -
-					offsetof(struct bfq_group, stats);
-
-/* to be used by recursive prfill, sums live and dead stats recursively */
-static u64 bfqg_stat_pd_recursive_sum(struct blkg_policy_data *pd, int off)
-{
-	u64 sum = 0;
-
-	sum += blkg_stat_recursive_sum(pd_to_blkg(pd), &blkcg_policy_bfq, off);
-	sum += blkg_stat_recursive_sum(pd_to_blkg(pd), &blkcg_policy_bfq,
-				       off + dead_stats_off_delta);
-	return sum;
-}
-
-/* to be used by recursive prfill, sums live and dead rwstats recursively */
-static struct blkg_rwstat bfqg_rwstat_pd_recursive_sum(struct blkg_policy_data *pd,
-						       int off)
-{
-	struct blkg_rwstat a, b;
-
-	a = blkg_rwstat_recursive_sum(pd_to_blkg(pd), &blkcg_policy_bfq, off);
-	b = blkg_rwstat_recursive_sum(pd_to_blkg(pd), &blkcg_policy_bfq,
-				      off + dead_stats_off_delta);
-	blkg_rwstat_add_aux(&a, &b);
-	return a;
-}
-
 static void bfq_pd_reset_stats(struct blkg_policy_data *pd)
 {
 	struct bfq_group *bfqg = pd_to_bfqg(pd);

 
 	bfqg_stats_reset(&bfqg->stats);
-	bfqg_stats_reset(&bfqg->dead_stats);
 }
 
-static struct bfq_group *bfq_find_alloc_group(struct bfq_data *bfqd,
-					      struct blkcg *blkcg)
+static void bfq_group_set_parent(struct bfq_group *bfqg,
+					struct bfq_group *parent)
 {
-	struct request_queue *q = bfqd->queue;
-	struct bfq_group *bfqg = NULL, *parent;
-	struct bfq_entity *entity = NULL;
+	struct bfq_entity *entity;
+
+	BUG_ON(!parent);
+	BUG_ON(!bfqg);
+	BUG_ON(bfqg == parent);
+
+	entity = &bfqg->entity;
+	entity->parent = parent->my_entity;
+	entity->sched_data = &parent->sched_data;
+}
+
+static struct bfq_group *bfq_lookup_bfqg(struct bfq_data *bfqd,
+					 struct blkcg *blkcg)
+{
+	struct blkcg_gq *blkg;
+
+	blkg = blkg_lookup(blkcg, bfqd->queue);
+	if (likely(blkg))
+		return blkg_to_bfqg(blkg);
+	return NULL;
+}
+
+static struct bfq_group *bfq_find_set_group(struct bfq_data *bfqd,
+					    struct blkcg *blkcg)
+{
+	struct bfq_group *bfqg, *parent;
+	struct bfq_entity *entity;
 
 	assert_spin_locked(bfqd->queue->queue_lock);
 
-	/* avoid lookup for the common case where there's no blkcg */
-	if (blkcg == &blkcg_root) {
-		bfqg = bfqd->root_group;
-	} else {
-		struct blkcg_gq *blkg;
+	bfqg = bfq_lookup_bfqg(bfqd, blkcg);
 
-		blkg = blkg_lookup_create(blkcg, q);
-		if (!IS_ERR(blkg))
-			bfqg = blkg_to_bfqg(blkg);
-		else /* fallback to root_group */
-			bfqg = bfqd->root_group;
-	}
-
-	BUG_ON(!bfqg);
+	if (unlikely(!bfqg))
+		return NULL;
 
 	/*
 	 * Update chain of bfq_groups as we might be handling a leaf group
@@ -531,13 +495,18 @@ static struct bfq_group *bfq_find_alloc_group(struct bfq_data *bfqd,
 	return bfqg;
 }
 
-static void bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq);
+static void bfq_pos_tree_add_move(struct bfq_data *bfqd,
+				  struct bfq_queue *bfqq);
+
+static void bfq_bfqq_expire(struct bfq_data *bfqd,
+			    struct bfq_queue *bfqq,
+			    bool compensate,
+			    enum bfqq_expiration reason);
 
 /**
  * bfq_bfqq_move - migrate @bfqq to @bfqg.
  * @bfqd: queue descriptor.
  * @bfqq: the queue to move.
- * @entity: @bfqq's entity.
  * @bfqg: the group to move to.
  *
  * Move @bfqq to @bfqg, deactivating it from its old group and reactivating
@@ -548,26 +517,40 @@ static void bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq)
  * rcu_read_lock()).
  */
 static void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq,
-			  struct bfq_entity *entity, struct bfq_group *bfqg)
+			  struct bfq_group *bfqg)
 {
-	int busy, resume;
+	struct bfq_entity *entity = &bfqq->entity;
 
-	busy = bfq_bfqq_busy(bfqq);
-	resume = !RB_EMPTY_ROOT(&bfqq->sort_list);
-
-	BUG_ON(resume && !entity->on_st);
-	BUG_ON(busy && !resume && entity->on_st &&
+	BUG_ON(!bfq_bfqq_busy(bfqq) && !RB_EMPTY_ROOT(&bfqq->sort_list));
+	BUG_ON(!RB_EMPTY_ROOT(&bfqq->sort_list) && !entity->on_st);
+	BUG_ON(bfq_bfqq_busy(bfqq) && RB_EMPTY_ROOT(&bfqq->sort_list)
+	       && entity->on_st &&
 	       bfqq != bfqd->in_service_queue);
+	BUG_ON(!bfq_bfqq_busy(bfqq) && bfqq == bfqd->in_service_queue);
 
-	if (busy) {
-		BUG_ON(atomic_read(&bfqq->ref) < 2);
+	/* If bfqq is empty, then bfq_bfqq_expire also invokes
+	 * bfq_del_bfqq_busy, thereby removing bfqq and its entity
+	 * from data structures related to current group. Otherwise we
+	 * need to remove bfqq explicitly with bfq_deactivate_bfqq, as
+	 * we do below.
+	 */
+	if (bfqq == bfqd->in_service_queue)
+		bfq_bfqq_expire(bfqd, bfqd->in_service_queue,
+				false, BFQ_BFQQ_PREEMPTED);
 
-		if (!resume)
-			bfq_del_bfqq_busy(bfqd, bfqq, 0);
-		else
-			bfq_deactivate_bfqq(bfqd, bfqq, 0);
-	} else if (entity->on_st)
+	BUG_ON(entity->on_st && !bfq_bfqq_busy(bfqq)
+	    && &bfq_entity_service_tree(entity)->idle !=
+	       entity->tree);
+
+	BUG_ON(RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_bfqq_busy(bfqq));
+
+	if (bfq_bfqq_busy(bfqq))
+		bfq_deactivate_bfqq(bfqd, bfqq, 0);
+	else if (entity->on_st) {
+		BUG_ON(&bfq_entity_service_tree(entity)->idle !=
+		       entity->tree);
 		bfq_put_idle_entity(bfq_entity_service_tree(entity), entity);
+	}
 	bfqg_put(bfqq_group(bfqq));
 
 	/*
@@ -579,14 +562,17 @@ static void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 	entity->sched_data = &bfqg->sched_data;
 	bfqg_get(bfqg);
 
-	if (busy) {
+	BUG_ON(RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_bfqq_busy(bfqq));
+	if (bfq_bfqq_busy(bfqq)) {
 		bfq_pos_tree_add_move(bfqd, bfqq);
-		if (resume)
-			bfq_activate_bfqq(bfqd, bfqq);
+		bfq_activate_bfqq(bfqd, bfqq);
 	}
 
 	if (!bfqd->in_service_queue && !bfqd->rq_in_driver)
 		bfq_schedule_dispatch(bfqd);
+	BUG_ON(entity->on_st && !bfq_bfqq_busy(bfqq)
+	       && &bfq_entity_service_tree(entity)->idle !=
+	       entity->tree);
 }
 
 /**
@@ -613,7 +599,7 @@ static struct bfq_group *__bfq_bic_change_cgroup(struct bfq_data *bfqd,
 
 	lockdep_assert_held(bfqd->queue->queue_lock);
 
-	bfqg = bfq_find_alloc_group(bfqd, blkcg);
+	bfqg = bfq_find_set_group(bfqd, blkcg);
 	if (async_bfqq) {
 		entity = &async_bfqq->entity;
 
@@ -621,7 +607,8 @@ static struct bfq_group *__bfq_bic_change_cgroup(struct bfq_data *bfqd,
 			bic_set_bfqq(bic, NULL, 0);
 			bfq_log_bfqq(bfqd, async_bfqq,
 				     "bic_change_group: %p %d",
-				     async_bfqq, atomic_read(&async_bfqq->ref));
+				     async_bfqq,
+				     async_bfqq->ref);
 			bfq_put_queue(async_bfqq);
 		}
 	}
@@ -629,7 +616,7 @@ static struct bfq_group *__bfq_bic_change_cgroup(struct bfq_data *bfqd,
 	if (sync_bfqq) {
 		entity = &sync_bfqq->entity;
 		if (entity->sched_data != &bfqg->sched_data)
-			bfq_bfqq_move(bfqd, sync_bfqq, entity, bfqg);
+			bfq_bfqq_move(bfqd, sync_bfqq, bfqg);
 	}
 
 	return bfqg;
@@ -638,25 +625,23 @@ static struct bfq_group *__bfq_bic_change_cgroup(struct bfq_data *bfqd,
 static void bfq_bic_update_cgroup(struct bfq_io_cq *bic, struct bio *bio)
 {
 	struct bfq_data *bfqd = bic_to_bfqd(bic);
-	struct blkcg *blkcg;
 	struct bfq_group *bfqg = NULL;
-	uint64_t id;
+	uint64_t serial_nr;
 
 	rcu_read_lock();
-	blkcg = bio_blkcg(bio);
-	id = blkcg->css.serial_nr;
-	rcu_read_unlock();
+	serial_nr = bio_blkcg(bio)->css.serial_nr;
 
 	/*
 	 * Check whether blkcg has changed.  The condition may trigger
 	 * spuriously on a newly created cic but there's no harm.
 	 */
-	if (unlikely(!bfqd) || likely(bic->blkcg_id == id))
-		return;
+	if (unlikely(!bfqd) || likely(bic->blkcg_serial_nr == serial_nr))
+		goto out;
 
-	bfqg = __bfq_bic_change_cgroup(bfqd, bic, blkcg);
-	BUG_ON(!bfqg);
-	bic->blkcg_id = id;
+	bfqg = __bfq_bic_change_cgroup(bfqd, bic, bio_blkcg(bio));
+	bic->blkcg_serial_nr = serial_nr;
+out:
+	rcu_read_unlock();
 }
 
 /**
@@ -682,8 +667,7 @@ static void bfq_reparent_leaf_entity(struct bfq_data *bfqd,
 	struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
 
 	BUG_ON(!bfqq);
-	bfq_bfqq_move(bfqd, bfqq, entity, bfqd->root_group);
-	return;
+	bfq_bfqq_move(bfqd, bfqq, bfqd->root_group);
 }
 
 /**
@@ -711,16 +695,15 @@ static void bfq_reparent_active_entities(struct bfq_data *bfqd,
 	if (bfqg->sched_data.in_service_entity)
 		bfq_reparent_leaf_entity(bfqd,
 			bfqg->sched_data.in_service_entity);
-
-	return;
 }
 
 /**
- * bfq_destroy_group - destroy @bfqg.
- * @bfqg: the group being destroyed.
+ * bfq_pd_offline - deactivate the entity associated with @pd,
+ *		    and reparent its children entities.
+ * @pd: descriptor of the policy going offline.
  *
- * Destroy @bfqg, making sure that it is not referenced from its parent.
- * blkio already grabs the queue_lock for us, so no need to use RCU-based magic
+ * blkio already grabs the queue_lock for us, so no need to use
+ * RCU-based magic
  */
 static void bfq_pd_offline(struct blkg_policy_data *pd)
 {
@@ -779,6 +762,12 @@ static void bfq_pd_offline(struct blkg_policy_data *pd)
 	bfq_put_async_queues(bfqd, bfqg);
 	BUG_ON(entity->tree);
 
+	/*
+	 * @blkg is going offline and will be ignored by
+	 * blkg_[rw]stat_recursive_sum().  Transfer stats to the parent so
+	 * that they don't get lost.  If IOs complete after this point, the
+	 * stats for them will be lost.  Oh well...
+	 */
 	bfqg_stats_xfer_dead(bfqg);
 }
 
@@ -788,46 +777,35 @@ static void bfq_end_wr_async(struct bfq_data *bfqd)
 
 	list_for_each_entry(blkg, &bfqd->queue->blkg_list, q_node) {
 		struct bfq_group *bfqg = blkg_to_bfqg(blkg);
+		BUG_ON(!bfqg);
 
 		bfq_end_wr_async_queues(bfqd, bfqg);
 	}
 	bfq_end_wr_async_queues(bfqd, bfqd->root_group);
 }
 
-static u64 bfqio_cgroup_weight_read(struct cgroup_subsys_state *css,
-				       struct cftype *cftype)
-{
-	struct blkcg *blkcg = css_to_blkcg(css);
-	struct bfq_group_data *bfqgd = blkcg_to_bfqgd(blkcg);
-	int ret = -EINVAL;
-
-	spin_lock_irq(&blkcg->lock);
-	ret = bfqgd->weight;
-	spin_unlock_irq(&blkcg->lock);
-
-	return ret;
-}
-
-static int bfqio_cgroup_weight_read_dfl(struct seq_file *sf, void *v)
+static int bfq_io_show_weight(struct seq_file *sf, void *v)
 {
 	struct blkcg *blkcg = css_to_blkcg(seq_css(sf));
 	struct bfq_group_data *bfqgd = blkcg_to_bfqgd(blkcg);
+	unsigned int val = 0;
 
-	spin_lock_irq(&blkcg->lock);
-	seq_printf(sf, "%u\n", bfqgd->weight);
-	spin_unlock_irq(&blkcg->lock);
+	if (bfqgd)
+		val = bfqgd->weight;
+
+	seq_printf(sf, "%u\n", val);
 
 	return 0;
 }
 
-static int bfqio_cgroup_weight_write(struct cgroup_subsys_state *css,
-					struct cftype *cftype,
-					u64 val)
+static int bfq_io_set_weight_legacy(struct cgroup_subsys_state *css,
+				    struct cftype *cftype,
+				    u64 val)
 {
 	struct blkcg *blkcg = css_to_blkcg(css);
 	struct bfq_group_data *bfqgd = blkcg_to_bfqgd(blkcg);
 	struct blkcg_gq *blkg;
-	int ret = -EINVAL;
+	int ret = -ERANGE;
 
 	if (val < BFQ_MIN_WEIGHT || val > BFQ_MAX_WEIGHT)
 		return ret;
@@ -837,6 +815,7 @@ static int bfqio_cgroup_weight_write(struct cgroup_subsys_state *css,
 	bfqgd->weight = (unsigned short)val;
 	hlist_for_each_entry(blkg, &blkcg->blkg_list, blkcg_node) {
 		struct bfq_group *bfqg = blkg_to_bfqg(blkg);
+
 		if (!bfqg)
 			continue;
 		/*
@@ -871,13 +850,18 @@ static int bfqio_cgroup_weight_write(struct cgroup_subsys_state *css,
 	return ret;
 }
 
-static ssize_t bfqio_cgroup_weight_write_dfl(struct kernfs_open_file *of,
-					     char *buf, size_t nbytes,
-					     loff_t off)
+static ssize_t bfq_io_set_weight(struct kernfs_open_file *of,
+				 char *buf, size_t nbytes,
+				 loff_t off)
 {
+	u64 weight;
 	/* First unsigned long found in the file is used */
-	return bfqio_cgroup_weight_write(of_css(of), NULL,
-					 simple_strtoull(strim(buf), NULL, 0));
+	int ret = kstrtoull(strim(buf), 0, &weight);
+
+	if (ret)
+		return ret;
+
+	return bfq_io_set_weight_legacy(of_css(of), NULL, weight);
 }
 
 static int bfqg_print_stat(struct seq_file *sf, void *v)
@@ -897,16 +881,17 @@ static int bfqg_print_rwstat(struct seq_file *sf, void *v)
 static u64 bfqg_prfill_stat_recursive(struct seq_file *sf,
 				      struct blkg_policy_data *pd, int off)
 {
-	u64 sum = bfqg_stat_pd_recursive_sum(pd, off);
-
+	u64 sum = blkg_stat_recursive_sum(pd_to_blkg(pd),
+					  &blkcg_policy_bfq, off);
 	return __blkg_prfill_u64(sf, pd, sum);
 }
 
 static u64 bfqg_prfill_rwstat_recursive(struct seq_file *sf,
 					struct blkg_policy_data *pd, int off)
 {
-	struct blkg_rwstat sum = bfqg_rwstat_pd_recursive_sum(pd, off);
-
+	struct blkg_rwstat sum = blkg_rwstat_recursive_sum(pd_to_blkg(pd),
+							   &blkcg_policy_bfq,
+							   off);
 	return __blkg_prfill_rwstat(sf, pd, &sum);
 }
 
@@ -926,6 +911,41 @@ static int bfqg_print_rwstat_recursive(struct seq_file *sf, void *v)
 	return 0;
 }
 
+static u64 bfqg_prfill_sectors(struct seq_file *sf, struct blkg_policy_data *pd,
+			       int off)
+{
+	u64 sum = blkg_rwstat_total(&pd->blkg->stat_bytes);
+
+	return __blkg_prfill_u64(sf, pd, sum >> 9);
+}
+
+static int bfqg_print_stat_sectors(struct seq_file *sf, void *v)
+{
+	blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
+			  bfqg_prfill_sectors, &blkcg_policy_bfq, 0, false);
+	return 0;
+}
+
+static u64 bfqg_prfill_sectors_recursive(struct seq_file *sf,
+					 struct blkg_policy_data *pd, int off)
+{
+	struct blkg_rwstat tmp = blkg_rwstat_recursive_sum(pd->blkg, NULL,
+					offsetof(struct blkcg_gq, stat_bytes));
+	u64 sum = atomic64_read(&tmp.aux_cnt[BLKG_RWSTAT_READ]) +
+		atomic64_read(&tmp.aux_cnt[BLKG_RWSTAT_WRITE]);
+
+	return __blkg_prfill_u64(sf, pd, sum >> 9);
+}
+
+static int bfqg_print_stat_sectors_recursive(struct seq_file *sf, void *v)
+{
+	blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
+			  bfqg_prfill_sectors_recursive, &blkcg_policy_bfq, 0,
+			  false);
+	return 0;
+}
+
+
 static u64 bfqg_prfill_avg_queue_size(struct seq_file *sf,
 				      struct blkg_policy_data *pd, int off)
 {
@@ -950,7 +970,8 @@ static int bfqg_print_avg_queue_size(struct seq_file *sf, void *v)
 	return 0;
 }
 
-static struct bfq_group *bfq_create_group_hierarchy(struct bfq_data *bfqd, int node)
+static struct bfq_group *
+bfq_create_group_hierarchy(struct bfq_data *bfqd, int node)
 {
 	int ret;
 
@@ -958,41 +979,18 @@ static struct bfq_group *bfq_create_group_hierarchy(struct bfq_data *bfqd, int n
 	if (ret)
 		return NULL;
 
-        return blkg_to_bfqg(bfqd->queue->root_blkg);
+	return blkg_to_bfqg(bfqd->queue->root_blkg);
 }
 
-static struct blkcg_policy_data *bfq_cpd_alloc(gfp_t gfp)
-{
-        struct bfq_group_data *bgd;
-
-        bgd = kzalloc(sizeof(*bgd), GFP_KERNEL);
-        if (!bgd)
-                return NULL;
-        return &bgd->pd;
-}
-
-static void bfq_cpd_free(struct blkcg_policy_data *cpd)
-{
-        kfree(cpd_to_bfqgd(cpd));
-}
-
-static struct cftype bfqio_files_dfl[] = {
-	{
-		.name = "weight",
-		.flags = CFTYPE_NOT_ON_ROOT,
-		.seq_show = bfqio_cgroup_weight_read_dfl,
-		.write = bfqio_cgroup_weight_write_dfl,
-	},
-	{} /* terminate */
-};
-
-static struct cftype bfqio_files[] = {
+static struct cftype bfq_blkcg_legacy_files[] = {
 	{
 		.name = "bfq.weight",
-		.read_u64 = bfqio_cgroup_weight_read,
-		.write_u64 = bfqio_cgroup_weight_write,
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.seq_show = bfq_io_show_weight,
+		.write_u64 = bfq_io_set_weight_legacy,
 	},
-	/* statistics, cover only the tasks in the bfqg */
+
+	/* statistics, covers only the tasks in the bfqg */
 	{
 		.name = "bfq.time",
 		.private = offsetof(struct bfq_group, stats.time),
@@ -1000,18 +998,17 @@ static struct cftype bfqio_files[] = {
 	},
 	{
 		.name = "bfq.sectors",
-		.private = offsetof(struct bfq_group, stats.sectors),
-		.seq_show = bfqg_print_stat,
+		.seq_show = bfqg_print_stat_sectors,
 	},
 	{
 		.name = "bfq.io_service_bytes",
-		.private = offsetof(struct bfq_group, stats.service_bytes),
-		.seq_show = bfqg_print_rwstat,
+		.private = (unsigned long)&blkcg_policy_bfq,
+		.seq_show = blkg_print_stat_bytes,
 	},
 	{
 		.name = "bfq.io_serviced",
-		.private = offsetof(struct bfq_group, stats.serviced),
-		.seq_show = bfqg_print_rwstat,
+		.private = (unsigned long)&blkcg_policy_bfq,
+		.seq_show = blkg_print_stat_ios,
 	},
 	{
 		.name = "bfq.io_service_time",
@@ -1042,18 +1039,17 @@ static struct cftype bfqio_files[] = {
 	},
 	{
 		.name = "bfq.sectors_recursive",
-		.private = offsetof(struct bfq_group, stats.sectors),
-		.seq_show = bfqg_print_stat_recursive,
+		.seq_show = bfqg_print_stat_sectors_recursive,
 	},
 	{
 		.name = "bfq.io_service_bytes_recursive",
-		.private = offsetof(struct bfq_group, stats.service_bytes),
-		.seq_show = bfqg_print_rwstat_recursive,
+		.private = (unsigned long)&blkcg_policy_bfq,
+		.seq_show = blkg_print_stat_bytes_recursive,
 	},
 	{
 		.name = "bfq.io_serviced_recursive",
-		.private = offsetof(struct bfq_group, stats.serviced),
-		.seq_show = bfqg_print_rwstat_recursive,
+		.private = (unsigned long)&blkcg_policy_bfq,
+		.seq_show = blkg_print_stat_ios_recursive,
 	},
 	{
 		.name = "bfq.io_service_time_recursive",
@@ -1099,32 +1095,35 @@ static struct cftype bfqio_files[] = {
 		.private = offsetof(struct bfq_group, stats.dequeue),
 		.seq_show = bfqg_print_stat,
 	},
-	{
-		.name = "bfq.unaccounted_time",
-		.private = offsetof(struct bfq_group, stats.unaccounted_time),
-		.seq_show = bfqg_print_stat,
-	},
 	{ }	/* terminate */
 };
 
-static struct blkcg_policy blkcg_policy_bfq = {
-       .dfl_cftypes            = bfqio_files_dfl,
-       .legacy_cftypes         = bfqio_files,
-
-       .pd_alloc_fn            = bfq_pd_alloc,
-       .pd_init_fn             = bfq_pd_init,
-       .pd_offline_fn          = bfq_pd_offline,
-       .pd_free_fn             = bfq_pd_free,
-       .pd_reset_stats_fn      = bfq_pd_reset_stats,
-
-       .cpd_alloc_fn           = bfq_cpd_alloc,
-       .cpd_init_fn            = bfq_cpd_init,
-       .cpd_bind_fn	       = bfq_cpd_init,
-       .cpd_free_fn            = bfq_cpd_free,
-
+static struct cftype bfq_blkg_files[] = {
+	{
+		.name = "bfq.weight",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.seq_show = bfq_io_show_weight,
+		.write = bfq_io_set_weight,
+	},
+	{} /* terminate */
 };
 
-#else
+#else /* CONFIG_BFQ_GROUP_IOSCHED */
+
+static inline void bfqg_stats_update_io_add(struct bfq_group *bfqg,
+			struct bfq_queue *bfqq, int rw) { }
+static inline void bfqg_stats_update_io_remove(struct bfq_group *bfqg, int rw) { }
+static inline void bfqg_stats_update_io_merged(struct bfq_group *bfqg, int rw) { }
+static inline void bfqg_stats_update_completion(struct bfq_group *bfqg,
+			uint64_t start_time, uint64_t io_start_time, int rw) { }
+static inline void bfqg_stats_set_start_group_wait_time(struct bfq_group *bfqg,
+struct bfq_group *curr_bfqg) { }
+static inline void bfqg_stats_end_empty_time(struct bfqg_stats *stats) { }
+static inline void bfqg_stats_update_dequeue(struct bfq_group *bfqg) { }
+static inline void bfqg_stats_set_start_empty_time(struct bfq_group *bfqg) { }
+static inline void bfqg_stats_update_idle_time(struct bfq_group *bfqg) { }
+static inline void bfqg_stats_set_start_idle_time(struct bfq_group *bfqg) { }
+static inline void bfqg_stats_update_avg_queue_size(struct bfq_group *bfqg) { }
 
 static void bfq_init_entity(struct bfq_entity *entity,
 			    struct bfq_group *bfqg)
@@ -1146,29 +1145,22 @@ bfq_bic_update_cgroup(struct bfq_io_cq *bic, struct bio *bio)
 	return bfqd->root_group;
 }
 
-static void bfq_bfqq_move(struct bfq_data *bfqd,
-			  struct bfq_queue *bfqq,
-			  struct bfq_entity *entity,
-			  struct bfq_group *bfqg)
-{
-}
-
 static void bfq_end_wr_async(struct bfq_data *bfqd)
 {
 	bfq_end_wr_async_queues(bfqd, bfqd->root_group);
 }
 
-static void bfq_disconnect_groups(struct bfq_data *bfqd)
-{
-	bfq_put_async_queues(bfqd, bfqd->root_group);
-}
-
-static struct bfq_group *bfq_find_alloc_group(struct bfq_data *bfqd,
+static struct bfq_group *bfq_find_set_group(struct bfq_data *bfqd,
                                               struct blkcg *blkcg)
 {
 	return bfqd->root_group;
 }
 
+static struct bfq_group *bfqq_group(struct bfq_queue *bfqq)
+{
+	return bfqq->bfqd->root_group;
+}
+
 static struct bfq_group *bfq_create_group_hierarchy(struct bfq_data *bfqd, int node)
 {
 	struct bfq_group *bfqg;
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index d1f648d05375..3bc1f8b16191 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -7,25 +7,26 @@
  * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
  *		      Paolo Valente <paolo.valente@unimore.it>
  *
- * Copyright (C) 2010 Paolo Valente <paolo.valente@unimore.it>
+ * Copyright (C) 2016 Paolo Valente <paolo.valente@unimore.it>
  *
  * Licensed under the GPL-2 as detailed in the accompanying COPYING.BFQ
  * file.
  *
- * BFQ is a proportional-share storage-I/O scheduling algorithm based on
- * the slice-by-slice service scheme of CFQ. But BFQ assigns budgets,
- * measured in number of sectors, to processes instead of time slices. The
- * device is not granted to the in-service process for a given time slice,
- * but until it has exhausted its assigned budget. This change from the time
- * to the service domain allows BFQ to distribute the device throughput
- * among processes as desired, without any distortion due to ZBR, workload
- * fluctuations or other factors. BFQ uses an ad hoc internal scheduler,
- * called B-WF2Q+, to schedule processes according to their budgets. More
- * precisely, BFQ schedules queues associated to processes. Thanks to the
- * accurate policy of B-WF2Q+, BFQ can afford to assign high budgets to
- * I/O-bound processes issuing sequential requests (to boost the
- * throughput), and yet guarantee a low latency to interactive and soft
- * real-time applications.
+ * BFQ is a proportional-share storage-I/O scheduling algorithm based
+ * on the slice-by-slice service scheme of CFQ. But BFQ assigns
+ * budgets, measured in number of sectors, to processes instead of
+ * time slices. The device is not granted to the in-service process
+ * for a given time slice, but until it has exhausted its assigned
+ * budget. This change from the time to the service domain enables BFQ
+ * to distribute the device throughput among processes as desired,
+ * without any distortion due to throughput fluctuations, or to device
+ * internal queueing. BFQ uses an ad hoc internal scheduler, called
+ * B-WF2Q+, to schedule processes according to their budgets. More
+ * precisely, BFQ schedules queues associated with processes. Thanks to
+ * the accurate policy of B-WF2Q+, BFQ can afford to assign high
+ * budgets to I/O-bound processes issuing sequential requests (to
+ * boost the throughput), and yet guarantee a low latency to
+ * interactive and soft real-time applications.
  *
  * BFQ is described in [1], where also a reference to the initial, more
  * theoretical paper on BFQ can be found. The interested reader can find
@@ -87,7 +88,6 @@ static const int bfq_stats_min_budgets = 194;
 
 /* Default maximum budget values, in sectors and number of requests. */
 static const int bfq_default_max_budget = 16 * 1024;
-static const int bfq_max_budget_async_rq = 4;
 
 /*
  * Async to sync throughput distribution is controlled as follows:
@@ -97,8 +97,7 @@ static const int bfq_max_budget_async_rq = 4;
 static const int bfq_async_charge_factor = 10;
 
 /* Default timeout values, in jiffies, approximating CFQ defaults. */
-static const int bfq_timeout_sync = HZ / 8;
-static int bfq_timeout_async = HZ / 25;
+static const int bfq_timeout = HZ / 8;
 
 struct kmem_cache *bfq_pool;
 
@@ -109,8 +108,9 @@ struct kmem_cache *bfq_pool;
 #define BFQ_HW_QUEUE_THRESHOLD	4
 #define BFQ_HW_QUEUE_SAMPLES	32
 
-#define BFQQ_SEEK_THR	 (sector_t)(8 * 1024)
-#define BFQQ_SEEKY(bfqq) ((bfqq)->seek_mean > BFQQ_SEEK_THR)
+#define BFQQ_SEEK_THR	 	(sector_t)(8 * 100)
+#define BFQQ_CLOSE_THR		(sector_t)(8 * 1024)
+#define BFQQ_SEEKY(bfqq)	(hweight32(bfqq->seek_history) > 32/8)
 
 /* Min samples used for peak rate estimation (for autotuning). */
 #define BFQ_PEAK_RATE_SAMPLES	32
@@ -141,16 +141,24 @@ struct kmem_cache *bfq_pool;
  * The device's speed class is dynamically (re)detected in
  * bfq_update_peak_rate() every time the estimated peak rate is updated.
  *
- * In the following definitions, R_slow[0]/R_fast[0] and T_slow[0]/T_fast[0]
- * are the reference values for a slow/fast rotational device, whereas
- * R_slow[1]/R_fast[1] and T_slow[1]/T_fast[1] are the reference values for
- * a slow/fast non-rotational device. Finally, device_speed_thresh are the
- * thresholds used to switch between speed classes.
+ * In the following definitions, R_slow[0]/R_fast[0] and
+ * T_slow[0]/T_fast[0] are the reference values for a slow/fast
+ * rotational device, whereas R_slow[1]/R_fast[1] and
+ * T_slow[1]/T_fast[1] are the reference values for a slow/fast
+ * non-rotational device. Finally, device_speed_thresh are the
+ * thresholds used to switch between speed classes. The reference
+ * rates are not the actual peak rates of the devices used as a
+ * reference, but slightly lower values. The reason for using these
+ * slightly lower values is that the peak-rate estimator tends to
+ * yield slightly lower values than the actual peak rate (it can yield
+ * the actual peak rate only if there is only one process doing I/O,
+ * and the process does sequential I/O).
+ *
  * Both the reference peak rates and the thresholds are measured in
  * sectors/usec, left-shifted by BFQ_RATE_SHIFT.
  */
-static int R_slow[2] = {1536, 10752};
-static int R_fast[2] = {17415, 34791};
+static int R_slow[2] = {1000, 10700};
+static int R_fast[2] = {14000, 33000};
 /*
  * To improve readability, a conversion function is used to initialize the
  * following arrays, which entails that they can be initialized only in a
@@ -410,11 +418,7 @@ static bool bfq_differentiated_weights(struct bfq_data *bfqd)
  */
 static bool bfq_symmetric_scenario(struct bfq_data *bfqd)
 {
-	return
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
-		!bfqd->active_numerous_groups &&
-#endif
-		!bfq_differentiated_weights(bfqd);
+	return !bfq_differentiated_weights(bfqd);
 }
 
 /*
@@ -534,9 +538,19 @@ static struct request *bfq_find_next_rq(struct bfq_data *bfqd,
 static unsigned long bfq_serv_to_charge(struct request *rq,
 					struct bfq_queue *bfqq)
 {
-	return blk_rq_sectors(rq) *
-		(1 + ((!bfq_bfqq_sync(bfqq)) * (bfqq->wr_coeff == 1) *
-		bfq_async_charge_factor));
+	if (bfq_bfqq_sync(bfqq) || bfqq->wr_coeff > 1)
+		return blk_rq_sectors(rq);
+
+	/*
+	 * If there are no weight-raised queues, then amplify service
+	 * by just the async charge factor; otherwise amplify service
+	 * by twice the async charge factor, to further reduce latency
+	 * for weight-raised queues.
+	 */
+	if (bfqq->bfqd->wr_busy_queues == 0)
+		return blk_rq_sectors(rq) * bfq_async_charge_factor;
+
+	return blk_rq_sectors(rq) * 2 * bfq_async_charge_factor;
 }
 
 /**
@@ -591,14 +605,25 @@ static unsigned int bfq_wr_duration(struct bfq_data *bfqd)
 	dur = bfqd->RT_prod;
 	do_div(dur, bfqd->peak_rate);
 
+	/*
+	 * Limit duration between 3 and 13 seconds. Tests show that
+	 * higher values than 13 seconds often yield the opposite of
+	 * the desired result, i.e., worsen responsiveness by letting
+	 * non-interactive and non-soft-real-time applications
+	 * preserve weight raising for a too long time interval.
+	 *
+	 * On the other end, lower values than 3 seconds make it
+	 * difficult for most interactive tasks to complete their jobs
+	 * before weight-raising finishes.
+	 */
+	if (dur > msecs_to_jiffies(13000))
+		dur = msecs_to_jiffies(13000);
+	else if (dur < msecs_to_jiffies(3000))
+		dur = msecs_to_jiffies(3000);
+
 	return dur;
 }
 
-static unsigned bfq_bfqq_cooperations(struct bfq_queue *bfqq)
-{
-	return bfqq->bic ? bfqq->bic->cooperations : 0;
-}
-
 static void
 bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_io_cq *bic)
 {
@@ -606,31 +631,11 @@ bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_io_cq *bic)
 		bfq_mark_bfqq_idle_window(bfqq);
 	else
 		bfq_clear_bfqq_idle_window(bfqq);
+
 	if (bic->saved_IO_bound)
 		bfq_mark_bfqq_IO_bound(bfqq);
 	else
 		bfq_clear_bfqq_IO_bound(bfqq);
-	/* Assuming that the flag in_large_burst is already correctly set */
-	if (bic->wr_time_left && bfqq->bfqd->low_latency &&
-	    !bfq_bfqq_in_large_burst(bfqq) &&
-	    bic->cooperations < bfqq->bfqd->bfq_coop_thresh) {
-		/*
-		 * Start a weight raising period with the duration given by
-		 * the raising_time_left snapshot.
-		 */
-		if (bfq_bfqq_busy(bfqq))
-			bfqq->bfqd->wr_busy_queues++;
-		bfqq->wr_coeff = bfqq->bfqd->bfq_wr_coeff;
-		bfqq->wr_cur_max_time = bic->wr_time_left;
-		bfqq->last_wr_start_finish = jiffies;
-		bfqq->entity.prio_changed = 1;
-	}
-	/*
-	 * Clear wr_time_left to prevent bfq_bfqq_save_state() from
-	 * getting confused about the queue's need of a weight-raising
-	 * period.
-	 */
-	bic->wr_time_left = 0;
 }
 
 static int bfqq_process_refs(struct bfq_queue *bfqq)
@@ -640,7 +645,7 @@ static int bfqq_process_refs(struct bfq_queue *bfqq)
 	lockdep_assert_held(bfqq->bfqd->queue->queue_lock);
 
 	io_refs = bfqq->allocated[READ] + bfqq->allocated[WRITE];
-	process_refs = atomic_read(&bfqq->ref) - io_refs - bfqq->entity.on_st;
+	process_refs = bfqq->ref - io_refs - bfqq->entity.on_st;
 	BUG_ON(process_refs < 0);
 	return process_refs;
 }
@@ -655,6 +660,7 @@ static void bfq_reset_burst_list(struct bfq_data *bfqd, struct bfq_queue *bfqq)
 		hlist_del_init(&item->burst_list_node);
 	hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
 	bfqd->burst_size = 1;
+	bfqd->burst_parent_entity = bfqq->entity.parent;
 }
 
 /* Add bfqq to the list of queues in current burst (see bfq_handle_burst) */
@@ -663,6 +669,10 @@ static void bfq_add_to_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
 	/* Increment burst size to take into account also bfqq */
 	bfqd->burst_size++;
 
+	bfq_log_bfqq(bfqd, bfqq, "add_to_burst %d", bfqd->burst_size);
+
+	BUG_ON(bfqd->burst_size > bfqd->bfq_large_burst_thresh);
+
 	if (bfqd->burst_size == bfqd->bfq_large_burst_thresh) {
 		struct bfq_queue *pos, *bfqq_item;
 		struct hlist_node *n;
@@ -672,15 +682,19 @@ static void bfq_add_to_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
 		 * other to consider this burst as large.
 		 */
 		bfqd->large_burst = true;
+		bfq_log_bfqq(bfqd, bfqq, "add_to_burst: large burst started");
 
 		/*
 		 * We can now mark all queues in the burst list as
 		 * belonging to a large burst.
 		 */
 		hlist_for_each_entry(bfqq_item, &bfqd->burst_list,
-				     burst_list_node)
+				     burst_list_node) {
 		        bfq_mark_bfqq_in_large_burst(bfqq_item);
+			bfq_log_bfqq(bfqd, bfqq_item, "marked in large burst");
+		}
 		bfq_mark_bfqq_in_large_burst(bfqq);
+		bfq_log_bfqq(bfqd, bfqq, "marked in large burst");
 
 		/*
 		 * From now on, and until the current burst finishes, any
@@ -692,67 +706,79 @@ static void bfq_add_to_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
 		hlist_for_each_entry_safe(pos, n, &bfqd->burst_list,
 					  burst_list_node)
 			hlist_del_init(&pos->burst_list_node);
-	} else /* burst not yet large: add bfqq to the burst list */
+	} else /*
+		* Burst not yet large: add bfqq to the burst list. Do
+		* not increment the ref counter for bfqq, because bfqq
+		* is removed from the burst list before freeing bfqq
+		* in put_queue.
+		*/
 		hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
 }
 
 /*
- * If many queues happen to become active shortly after each other, then,
- * to help the processes associated to these queues get their job done as
- * soon as possible, it is usually better to not grant either weight-raising
- * or device idling to these queues. In this comment we describe, firstly,
- * the reasons why this fact holds, and, secondly, the next function, which
- * implements the main steps needed to properly mark these queues so that
- * they can then be treated in a different way.
+ * If many queues belonging to the same group happen to be created
+ * shortly after each other, then the processes associated with these
+ * queues have typically a common goal. In particular, bursts of queue
+ * creations are usually caused by services or applications that spawn
+ * many parallel threads/processes. Examples are systemd during boot,
+ * or git grep. To help these processes get their job done as soon as
+ * possible, it is usually better to not grant either weight-raising
+ * or device idling to their queues.
  *
- * As for the terminology, we say that a queue becomes active, i.e.,
- * switches from idle to backlogged, either when it is created (as a
- * consequence of the arrival of an I/O request), or, if already existing,
- * when a new request for the queue arrives while the queue is idle.
- * Bursts of activations, i.e., activations of different queues occurring
- * shortly after each other, are typically caused by services or applications
- * that spawn or reactivate many parallel threads/processes. Examples are
- * systemd during boot or git grep.
+ * In this comment we describe, firstly, the reasons why this fact
+ * holds, and, secondly, the next function, which implements the main
+ * steps needed to properly mark these queues so that they can then be
+ * treated in a different way.
  *
- * These services or applications benefit mostly from a high throughput:
- * the quicker the requests of the activated queues are cumulatively served,
- * the sooner the target job of these queues gets completed. As a consequence,
- * weight-raising any of these queues, which also implies idling the device
- * for it, is almost always counterproductive: in most cases it just lowers
- * throughput.
+ * The above services or applications benefit mostly from a high
+ * throughput: the quicker the requests of the activated queues are
+ * cumulatively served, the sooner the target job of these queues gets
+ * completed. As a consequence, weight-raising any of these queues,
+ * which also implies idling the device for it, is almost always
+ * counterproductive. In most cases it just lowers throughput.
  *
- * On the other hand, a burst of activations may be also caused by the start
- * of an application that does not consist in a lot of parallel I/O-bound
- * threads. In fact, with a complex application, the burst may be just a
- * consequence of the fact that several processes need to be executed to
- * start-up the application. To start an application as quickly as possible,
- * the best thing to do is to privilege the I/O related to the application
- * with respect to all other I/O. Therefore, the best strategy to start as
- * quickly as possible an application that causes a burst of activations is
- * to weight-raise all the queues activated during the burst. This is the
+ * On the other hand, a burst of queue creations may be caused also by
+ * the start of an application that does not consist of a lot of
+ * parallel I/O-bound threads. In fact, with a complex application,
+ * several short processes may need to be executed to start-up the
+ * application. In this respect, to start an application as quickly as
+ * possible, the best thing to do is in any case to privilege the I/O
+ * related to the application with respect to all other
+ * I/O. Therefore, the best strategy to start as quickly as possible
+ * an application that causes a burst of queue creations is to
+ * weight-raise all the queues created during the burst. This is the
  * exact opposite of the best strategy for the other type of bursts.
  *
- * In the end, to take the best action for each of the two cases, the two
- * types of bursts need to be distinguished. Fortunately, this seems
- * relatively easy to do, by looking at the sizes of the bursts. In
- * particular, we found a threshold such that bursts with a larger size
- * than that threshold are apparently caused only by services or commands
- * such as systemd or git grep. For brevity, hereafter we call just 'large'
- * these bursts. BFQ *does not* weight-raise queues whose activations occur
- * in a large burst. In addition, for each of these queues BFQ performs or
- * does not perform idling depending on which choice boosts the throughput
- * most. The exact choice depends on the device and request pattern at
+ * In the end, to take the best action for each of the two cases, the
+ * two types of bursts need to be distinguished. Fortunately, this
+ * seems relatively easy, by looking at the sizes of the bursts. In
+ * particular, we found a threshold such that only bursts with a
+ * larger size than that threshold are apparently caused by
+ * services or commands such as systemd or git grep. For brevity,
+ * hereafter we call just 'large' these bursts. BFQ *does not*
+ * weight-raise queues whose creation occurs in a large burst. In
+ * addition, for each of these queues BFQ performs or does not perform
+ * idling depending on which choice boosts the throughput more. The
+ * exact choice depends on the device and request pattern at
  * hand.
  *
- * Turning back to the next function, it implements all the steps needed
- * to detect the occurrence of a large burst and to properly mark all the
- * queues belonging to it (so that they can then be treated in a different
- * way). This goal is achieved by maintaining a special "burst list" that
- * holds, temporarily, the queues that belong to the burst in progress. The
- * list is then used to mark these queues as belonging to a large burst if
- * the burst does become large. The main steps are the following.
+ * Unfortunately, false positives may occur while an interactive task
+ * is starting (e.g., an application is being started). The
+ * consequence is that the queues associated with the task do not
+ * enjoy weight raising as expected. Fortunately these false positives
+ * are very rare. They typically occur if some service happens to
+ * start doing I/O exactly when the interactive task starts.
  *
- * . when the very first queue is activated, the queue is inserted into the
+ * Turning back to the next function, it implements all the steps
+ * needed to detect the occurrence of a large burst and to properly
+ * mark all the queues belonging to it (so that they can then be
+ * treated in a different way). This goal is achieved by maintaining a
+ * "burst list" that holds, temporarily, the queues that belong to the
+ * burst in progress. The list is then used to mark these queues as
+ * belonging to a large burst if the burst does become large. The main
+ * steps are the following.
+ *
+ * . when the very first queue is created, the queue is inserted into the
  *   list (as it could be the first queue in a possible burst)
  *
  * . if the current burst has not yet become large, and a queue Q that does
@@ -773,13 +799,13 @@ static void bfq_add_to_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
  *
  *     . the device enters a large-burst mode
  *
- * . if a queue Q that does not belong to the burst is activated while
+ * . if a queue Q that does not belong to the burst is created while
  *   the device is in large-burst mode and shortly after the last time
  *   at which a queue either entered the burst list or was marked as
  *   belonging to the current large burst, then Q is immediately marked
  *   as belonging to a large burst.
  *
- * . if a queue Q that does not belong to the burst is activated a while
+ * . if a queue Q that does not belong to the burst is created a while
  *   later, i.e., not shortly after, than the last time at which a queue
  *   either entered the burst list or was marked as belonging to the
  *   current large burst, then the current burst is deemed as finished and:
@@ -792,52 +818,44 @@ static void bfq_add_to_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
  *          in a possible new burst (then the burst list contains just Q
  *          after this step).
  */
-static void bfq_handle_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq,
-			     bool idle_for_long_time)
+static void bfq_handle_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
 {
-	/*
-	 * If bfqq happened to be activated in a burst, but has been idle
-	 * for at least as long as an interactive queue, then we assume
-	 * that, in the overall I/O initiated in the burst, the I/O
-	 * associated to bfqq is finished. So bfqq does not need to be
-	 * treated as a queue belonging to a burst anymore. Accordingly,
-	 * we reset bfqq's in_large_burst flag if set, and remove bfqq
-	 * from the burst list if it's there. We do not decrement instead
-	 * burst_size, because the fact that bfqq does not need to belong
-	 * to the burst list any more does not invalidate the fact that
-	 * bfqq may have been activated during the current burst.
-	 */
-	if (idle_for_long_time) {
-		hlist_del_init(&bfqq->burst_list_node);
-		bfq_clear_bfqq_in_large_burst(bfqq);
-	}
-
 	/*
 	 * If bfqq is already in the burst list or is part of a large
-	 * burst, then there is nothing else to do.
+	 * burst, or finally has just been split, then there is
+	 * nothing else to do.
 	 */
 	if (!hlist_unhashed(&bfqq->burst_list_node) ||
-	    bfq_bfqq_in_large_burst(bfqq))
+	    bfq_bfqq_in_large_burst(bfqq) ||
+	    time_is_after_eq_jiffies(bfqq->split_time +
+				     msecs_to_jiffies(10)))
 		return;
 
 	/*
-	 * If bfqq's activation happens late enough, then the current
-	 * burst is finished, and related data structures must be reset.
+	 * If bfqq's creation happens late enough, or bfqq belongs to
+	 * a different group than the burst group, then the current
+	 * burst is finished, and related data structures must be
+	 * reset.
 	 *
-	 * In this respect, consider the special case where bfqq is the very
-	 * first queue being activated. In this case, last_ins_in_burst is
-	 * not yet significant when we get here. But it is easy to verify
-	 * that, whether or not the following condition is true, bfqq will
-	 * end up being inserted into the burst list. In particular the
-	 * list will happen to contain only bfqq. And this is exactly what
-	 * has to happen, as bfqq may be the first queue in a possible
+	 * In this respect, consider the special case where bfqq is
+	 * the very first queue created after BFQ is selected for this
+	 * device. In this case, last_ins_in_burst and
+	 * burst_parent_entity are not yet significant when we get
+	 * here. But it is easy to verify that, whether or not the
+	 * following condition is true, bfqq will end up being
+	 * inserted into the burst list. In particular the list will
+	 * happen to contain only bfqq. And this is exactly what has
+	 * to happen, as bfqq may be the first queue of the first
 	 * burst.
 	 */
 	if (time_is_before_jiffies(bfqd->last_ins_in_burst +
-	    bfqd->bfq_burst_interval)) {
+	    bfqd->bfq_burst_interval) ||
+	    bfqq->entity.parent != bfqd->burst_parent_entity) {
 		bfqd->large_burst = false;
 		bfq_reset_burst_list(bfqd, bfqq);
-		return;
+		bfq_log_bfqq(bfqd, bfqq,
+			"handle_burst: late activation or different group");
+		goto end;
 	}
 
 	/*
@@ -846,8 +864,9 @@ static void bfq_handle_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 	 * bfqq as belonging to this large burst immediately.
 	 */
 	if (bfqd->large_burst) {
+		bfq_log_bfqq(bfqd, bfqq, "handle_burst: marked in burst");
 		bfq_mark_bfqq_in_large_burst(bfqq);
-		return;
+		goto end;
 	}
 
 	/*
@@ -856,25 +875,498 @@ static void bfq_handle_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 	 * queue. Then we add bfqq to the burst.
 	 */
 	bfq_add_to_burst(bfqd, bfqq);
+end:
+	/*
+	 * At this point, bfqq either has been added to the current
+	 * burst or has caused the current burst to terminate and a
+	 * possible new burst to start. In particular, in the second
+	 * case, bfqq has become the first queue in the possible new
+	 * burst.  In both cases last_ins_in_burst needs to be moved
+	 * forward.
+	 */
+	bfqd->last_ins_in_burst = jiffies;
+
+}
+
+static int bfq_bfqq_budget_left(struct bfq_queue *bfqq)
+{
+	struct bfq_entity *entity = &bfqq->entity;
+	return entity->budget - entity->service;
+}
+
+/*
+ * If enough samples have been computed, return the current max budget
+ * stored in bfqd, which is dynamically updated according to the
+ * estimated disk peak rate; otherwise return the default max budget
+ */
+static int bfq_max_budget(struct bfq_data *bfqd)
+{
+	if (bfqd->budgets_assigned < bfq_stats_min_budgets)
+		return bfq_default_max_budget;
+	else
+		return bfqd->bfq_max_budget;
+}
+
+/*
+ * Return min budget, which is a fraction of the current or default
+ * max budget (trying with 1/32)
+ */
+static int bfq_min_budget(struct bfq_data *bfqd)
+{
+	if (bfqd->budgets_assigned < bfq_stats_min_budgets)
+		return bfq_default_max_budget / 32;
+	else
+		return bfqd->bfq_max_budget / 32;
+}
+
+static void bfq_bfqq_expire(struct bfq_data *bfqd,
+			    struct bfq_queue *bfqq,
+			    bool compensate,
+			    enum bfqq_expiration reason);
+
+/*
+ * The next function, invoked after the input queue bfqq switches from
+ * idle to busy, updates the budget of bfqq. The function also tells
+ * whether the in-service queue should be expired, by returning
+ * true. The purpose of expiring the in-service queue is to give bfqq
+ * the chance to possibly preempt the in-service queue, and the reason
+ * for preempting the in-service queue is to achieve one of the two
+ * goals below.
+ *
+ * 1. Guarantee to bfqq its reserved bandwidth even if bfqq has
+ * expired because it has remained idle. In particular, bfqq may have
+ * expired for one of the following two reasons:
+ *
+ * - BFQ_BFQQ_NO_MORE_REQUEST bfqq did not enjoy any device idling and
+ *   did not make it to issue a new request before its last request
+ *   was served;
+ *
+ * - BFQ_BFQQ_TOO_IDLE bfqq did enjoy device idling, but did not issue
+ *   a new request before the expiration of the idling-time.
+ *
+ * Even if bfqq has expired for one of the above reasons, the process
+ * associated with the queue may be however issuing requests greedily,
+ * and thus be sensitive to the bandwidth it receives (bfqq may have
+ * remained idle for other reasons: CPU high load, bfqq not enjoying
+ * idling, I/O throttling somewhere in the path from the process to
+ * the I/O scheduler, ...). But if, after every expiration for one of
+ * the above two reasons, bfqq has to wait for the service of at least
+ * one full budget of another queue before being served again, then
+ * bfqq is likely to get a much lower bandwidth or resource time than
+ * its reserved ones. To address this issue, two countermeasures need
+ * to be taken.
+ *
+ * First, the budget and the timestamps of bfqq need to be updated in
+ * a special way on bfqq reactivation: they need to be updated as if
+ * bfqq did not remain idle and did not expire. In fact, if they are
+ * computed as if bfqq expired and remained idle until reactivation,
+ * then the process associated with bfqq is treated as if, instead of
+ * being greedy, it stopped issuing requests when bfqq remained idle,
+ * and restarts issuing requests only on this reactivation. In other
+ * words, the scheduler does not help the process recover the "service
+ * hole" between bfqq expiration and reactivation. As a consequence,
+ * the process receives a lower bandwidth than its reserved one. In
+ * contrast, to recover this hole, the budget must be updated as if
+ * bfqq was not expired at all before this reactivation, i.e., it must
+ * be set to the value of the remaining budget when bfqq was
+ * expired. Along the same line, timestamps need to be assigned the
+ * value they had the last time bfqq was selected for service, i.e.,
+ * before last expiration. Thus timestamps need to be back-shifted
+ * with respect to their normal computation (see [1] for more details
+ * on this tricky aspect).
+ *
+ * Secondly, to allow the process to recover the hole, the in-service
+ * queue must be expired too, to give bfqq the chance to preempt it
+ * immediately. In fact, if bfqq has to wait for a full budget of the
+ * in-service queue to be completed, then it may become impossible to
+ * let the process recover the hole, even if the back-shifted
+ * timestamps of bfqq are lower than those of the in-service queue. If
+ * this happens for most or all of the holes, then the process may not
+ * receive its reserved bandwidth. In this respect, it is worth noting
+ * that, being the service of outstanding requests unpreemptible, a
+ * little fraction of the holes may however be unrecoverable, thereby
+ * causing a little loss of bandwidth.
+ *
+ * The last important point is detecting whether bfqq does need this
+ * bandwidth recovery. In this respect, the next function deems the
+ * process associated with bfqq greedy, and thus allows it to recover
+ * the hole, if: 1) the process is waiting for the arrival of a new
+ * request (which implies that bfqq expired for one of the above two
+ * reasons), and 2) such a request has arrived soon. The first
+ * condition is controlled through the flag non_blocking_wait_rq,
+ * while the second through the flag arrived_in_time. If both
+ * conditions hold, then the function computes the budget in the
+ * above-described special way, and signals that the in-service queue
+ * should be expired. Timestamp back-shifting is done later in
+ * __bfq_activate_entity.
+ *
+ * 2. Reduce latency. Even if timestamps are not backshifted to let
+ * the process associated with bfqq recover a service hole, bfqq may
+ * however happen to have, after being (re)activated, a lower finish
+ * timestamp than the in-service queue.  That is, the next budget of
+ * bfqq may have to be completed before the one of the in-service
+ * queue. If this is the case, then preempting the in-service queue
+ * allows this goal to be achieved, apart from the unpreemptible,
+ * outstanding requests mentioned above.
+ *
+ * Unfortunately, regardless of which of the above two goals one wants
+ * to achieve, service trees need first to be updated to know whether
+ * the in-service queue must be preempted. To have service trees
+ * correctly updated, the in-service queue must be expired and
+ * rescheduled, and bfqq must be scheduled too. This is one of the
+ * most costly operations (in future versions, the scheduling
+ * mechanism may be re-designed in such a way to make it possible to
+ * know whether preemption is needed without needing to update service
+ * trees). In addition, queue preemptions almost always cause random
+ * I/O, and thus loss of throughput. Because of these facts, the next
+ * function adopts the following simple scheme to avoid both costly
+ * operations and too frequent preemptions: it requests the expiration
+ * of the in-service queue (unconditionally) only for queues that need
+ * to recover a hole, or that either are weight-raised or deserve to
+ * be weight-raised.
+ */
+static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd,
+						struct bfq_queue *bfqq,
+						bool arrived_in_time,
+						bool wr_or_deserves_wr)
+{
+	struct bfq_entity *entity = &bfqq->entity;
+
+	if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time) {
+		/*
+		 * We do not clear the flag non_blocking_wait_rq here, as
+		 * the latter is used in bfq_activate_bfqq to signal
+		 * that timestamps need to be back-shifted (and is
+		 * cleared right after).
+		 */
+
+		/*
+		 * In next assignment we rely on that either
+		 * entity->service or entity->budget are not updated
+		 * on expiration if bfqq is empty (see
+		 * __bfq_bfqq_recalc_budget). Thus both quantities
+		 * remain unchanged after such an expiration, and the
+		 * following statement therefore assigns to
+		 * entity->budget the remaining budget on such an
+		 * expiration. For clarity, entity->service is not
+		 * updated on expiration in any case, and, in normal
+		 * operation, is reset only when bfqq is selected for
+		 * service (see bfq_get_next_queue).
+		 */
+		entity->budget = min_t(unsigned long,
+				       bfq_bfqq_budget_left(bfqq),
+				       bfqq->max_budget);
+
+		BUG_ON(entity->budget < 0);
+		return true;
+	}
+
+	entity->budget = max_t(unsigned long, bfqq->max_budget,
+			       bfq_serv_to_charge(bfqq->next_rq,bfqq));
+	BUG_ON(entity->budget < 0);
+
+	bfq_clear_bfqq_non_blocking_wait_rq(bfqq);
+	return wr_or_deserves_wr;
+}
+
+static void bfq_update_bfqq_wr_on_rq_arrival(struct bfq_data *bfqd,
+					     struct bfq_queue *bfqq,
+					     unsigned int old_wr_coeff,
+					     bool wr_or_deserves_wr,
+					     bool interactive,
+					     bool in_burst,
+					     bool soft_rt)
+{
+	if (old_wr_coeff == 1 && wr_or_deserves_wr) {
+		/* start a weight-raising period */
+		if (interactive) {
+			bfqq->wr_coeff = bfqd->bfq_wr_coeff;
+			bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
+		} else {
+			bfqq->wr_coeff = bfqd->bfq_wr_coeff *
+				BFQ_SOFTRT_WEIGHT_FACTOR;
+			bfqq->wr_cur_max_time =
+				bfqd->bfq_wr_rt_max_time;
+		}
+		/*
+		 * If needed, further reduce budget to make sure it is
+		 * close to bfqq's backlog, so as to reduce the
+		 * scheduling-error component due to a too large
+		 * budget. Do not care about throughput consequences,
+		 * but only about latency. Finally, do not assign a
+		 * too small budget either, to avoid increasing
+		 * latency by causing too frequent expirations.
+		 */
+		bfqq->entity.budget = min_t(unsigned long,
+					    bfqq->entity.budget,
+					    2 * bfq_min_budget(bfqd));
+
+		bfq_log_bfqq(bfqd, bfqq,
+			     "wrais starting at %lu, rais_max_time %u",
+			     jiffies,
+			     jiffies_to_msecs(bfqq->wr_cur_max_time));
+	} else if (old_wr_coeff > 1) {
+		if (interactive) { /* update wr coeff and duration */
+			bfqq->wr_coeff = bfqd->bfq_wr_coeff;
+			bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
+		} else if (in_burst) {
+			bfqq->wr_coeff = 1;
+			bfq_log_bfqq(bfqd, bfqq,
+				     "wrais ending at %lu, rais_max_time %u",
+				     jiffies,
+				     jiffies_to_msecs(bfqq->
+						      wr_cur_max_time));
+		} else if (time_before(
+				   bfqq->last_wr_start_finish +
+				   bfqq->wr_cur_max_time,
+				   jiffies +
+				   bfqd->bfq_wr_rt_max_time) &&
+			   soft_rt) {
+			/*
+			 * The remaining weight-raising time is lower
+			 * than bfqd->bfq_wr_rt_max_time, which means
+			 * that the application is enjoying weight
+			 * raising either because deemed soft-rt in
+			 * the near past, or because deemed interactive
+			 * a long ago.
+			 * In both cases, resetting now the current
+			 * remaining weight-raising time for the
+			 * application to the weight-raising duration
+			 * for soft rt applications would not cause any
+			 * latency increase for the application (as the
+			 * new duration would be higher than the
+			 * remaining time).
+			 *
+			 * In addition, the application is now meeting
+			 * the requirements for being deemed soft rt.
+			 * In the end we can correctly and safely
+			 * (re)charge the weight-raising duration for
+			 * the application with the weight-raising
+			 * duration for soft rt applications.
+			 *
+			 * In particular, doing this recharge now, i.e.,
+			 * before the weight-raising period for the
+			 * application finishes, reduces the probability
+			 * of the following negative scenario:
+			 * 1) the weight of a soft rt application is
+			 *    raised at startup (as for any newly
+			 *    created application),
+			 * 2) since the application is not interactive,
+			 *    at a certain time weight-raising is
+			 *    stopped for the application,
+			 * 3) at that time the application happens to
+			 *    still have pending requests, and hence
+			 *    is destined to not have a chance to be
+			 *    deemed soft rt before these requests are
+			 *    completed (see the comments to the
+			 *    function bfq_bfqq_softrt_next_start()
+			 *    for details on soft rt detection),
+			 * 4) these pending requests experience a high
+			 *    latency because the application is not
+			 *    weight-raised while they are pending.
+			 */
+			bfqq->last_wr_start_finish = jiffies;
+			bfqq->wr_cur_max_time =
+				bfqd->bfq_wr_rt_max_time;
+			bfqq->wr_coeff = bfqd->bfq_wr_coeff *
+				BFQ_SOFTRT_WEIGHT_FACTOR;
+			bfq_log_bfqq(bfqd, bfqq,
+				     "switching to soft_rt wr, or "
+				     " just moving forward duration");
+		}
+	}
+}
+
+static bool bfq_bfqq_idle_for_long_time(struct bfq_data *bfqd,
+					struct bfq_queue *bfqq)
+{
+	return bfqq->dispatched == 0 &&
+		time_is_before_jiffies(
+			bfqq->budget_timeout +
+			bfqd->bfq_wr_min_idle_time);
+}
+
+static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
+					     struct bfq_queue *bfqq,
+					     int old_wr_coeff,
+					     struct request *rq,
+					     bool *interactive)
+{
+	bool soft_rt, in_burst,	wr_or_deserves_wr,
+		bfqq_wants_to_preempt,
+		idle_for_long_time = bfq_bfqq_idle_for_long_time(bfqd, bfqq),
+		/*
+		 * See the comments on
+		 * bfq_bfqq_update_budg_for_activation for
+		 * details on the usage of the next variable.
+		 */
+		arrived_in_time = time_is_after_jiffies(
+			RQ_BIC(rq)->ttime.last_end_request +
+			bfqd->bfq_slice_idle * 3);
+
+	bfq_log_bfqq(bfqd, bfqq,
+		     "bfq_add_request non-busy: "
+		     "jiffies %lu, in_time %d, idle_long %d busyw %d "
+		     "wr_coeff %u",
+		     jiffies, arrived_in_time,
+		     idle_for_long_time,
+		     bfq_bfqq_non_blocking_wait_rq(bfqq),
+		     old_wr_coeff);
+
+	BUG_ON(bfqq->entity.budget < bfqq->entity.service);
+
+	BUG_ON(bfqq == bfqd->in_service_queue);
+	bfqg_stats_update_io_add(bfqq_group(RQ_BFQQ(rq)), bfqq,
+				 rq->cmd_flags);
+
+	/*
+	 * bfqq deserves to be weight-raised if:
+	 * - it is sync,
+	 * - it does not belong to a large burst,
+	 * - it has been idle for enough time or is soft real-time,
+	 * - is linked to a bfq_io_cq (it is not shared in any sense)
+	 */
+	in_burst = bfq_bfqq_in_large_burst(bfqq);
+	soft_rt = bfqd->bfq_wr_max_softrt_rate > 0 &&
+		!in_burst &&
+		time_is_before_jiffies(bfqq->soft_rt_next_start);
+	*interactive =
+		!in_burst &&
+		idle_for_long_time;
+	wr_or_deserves_wr = bfqd->low_latency &&
+		(bfqq->wr_coeff > 1 ||
+		 (bfq_bfqq_sync(bfqq) &&
+		  bfqq->bic && (*interactive || soft_rt)));
+
+	bfq_log_bfqq(bfqd, bfqq,
+		     "bfq_add_request: "
+		     "in_burst %d, "
+		     "soft_rt %d (next %lu), inter %d, bic %p",
+		     bfq_bfqq_in_large_burst(bfqq), soft_rt,
+		     bfqq->soft_rt_next_start,
+		     *interactive,
+		     bfqq->bic);
+
+	/*
+	 * Using the last flag, update budget and check whether bfqq
+	 * may want to preempt the in-service queue.
+	 */
+	bfqq_wants_to_preempt =
+		bfq_bfqq_update_budg_for_activation(bfqd, bfqq,
+						    arrived_in_time,
+						    wr_or_deserves_wr);
+
+	/*
+	 * If bfqq happened to be activated in a burst, but has been
+	 * idle for much more than an interactive queue, then we
+	 * assume that, in the overall I/O initiated in the burst, the
+	 * I/O associated with bfqq is finished. So bfqq does not need
+	 * to be treated as a queue belonging to a burst
+	 * anymore. Accordingly, we reset bfqq's in_large_burst flag
+	 * if set, and remove bfqq from the burst list if it's
+	 * there. We do not decrement burst_size, because the fact
+	 * that bfqq does not need to belong to the burst list any
+	 * more does not invalidate the fact that bfqq was created in
+	 * a burst.
+	 */
+	if (likely(!bfq_bfqq_just_created(bfqq)) &&
+	    idle_for_long_time &&
+	    time_is_before_jiffies(
+		    bfqq->budget_timeout +
+		    msecs_to_jiffies(10000))) {
+		hlist_del_init(&bfqq->burst_list_node);
+		bfq_clear_bfqq_in_large_burst(bfqq);
+	}
+
+	bfq_clear_bfqq_just_created(bfqq);
+
+	if (!bfq_bfqq_IO_bound(bfqq)) {
+		if (arrived_in_time) {
+			bfqq->requests_within_timer++;
+			if (bfqq->requests_within_timer >=
+			    bfqd->bfq_requests_within_timer)
+				bfq_mark_bfqq_IO_bound(bfqq);
+		} else
+			bfqq->requests_within_timer = 0;
+		bfq_log_bfqq(bfqd, bfqq, "requests in time %d",
+			     bfqq->requests_within_timer);
+	}
+
+	if (bfqd->low_latency) {
+		if (unlikely(time_is_after_jiffies(bfqq->split_time)))
+			/* wraparound */
+			bfqq->split_time =
+				jiffies - bfqd->bfq_wr_min_idle_time - 1;
+
+		if (time_is_before_jiffies(bfqq->split_time +
+					   bfqd->bfq_wr_min_idle_time)) {
+			bfq_update_bfqq_wr_on_rq_arrival(bfqd, bfqq,
+							 old_wr_coeff,
+							 wr_or_deserves_wr,
+							 *interactive,
+							 in_burst,
+							 soft_rt);
+
+			if (old_wr_coeff != bfqq->wr_coeff)
+				bfqq->entity.prio_changed = 1;
+		}
+	}
+
+	bfqq->last_idle_bklogged = jiffies;
+	bfqq->service_from_backlogged = 0;
+	bfq_clear_bfqq_softrt_update(bfqq);
+
+	bfq_add_bfqq_busy(bfqd, bfqq);
+
+	/*
+	 * Expire in-service queue only if preemption may be needed
+	 * for guarantees. In this respect, the function
+	 * next_queue_may_preempt just checks a simple, necessary
+	 * condition, and not a sufficient condition based on
+	 * timestamps. In fact, for the latter condition to be
+	 * evaluated, timestamps would need first to be updated, and
+	 * this operation is quite costly (see the comments on the
+	 * function bfq_bfqq_update_budg_for_activation).
+	 */
+	if (bfqd->in_service_queue && bfqq_wants_to_preempt &&
+	    bfqd->in_service_queue->wr_coeff < bfqq->wr_coeff &&
+	    next_queue_may_preempt(bfqd)) {
+		struct bfq_queue *in_serv =
+			bfqd->in_service_queue;
+		BUG_ON(in_serv == bfqq);
+
+		bfq_bfqq_expire(bfqd, bfqd->in_service_queue,
+				false, BFQ_BFQQ_PREEMPTED);
+		BUG_ON(in_serv->entity.budget < 0);
+	}
 }
 
 static void bfq_add_request(struct request *rq)
 {
 	struct bfq_queue *bfqq = RQ_BFQQ(rq);
-	struct bfq_entity *entity = &bfqq->entity;
 	struct bfq_data *bfqd = bfqq->bfqd;
 	struct request *next_rq, *prev;
-	unsigned long old_wr_coeff = bfqq->wr_coeff;
+	unsigned int old_wr_coeff = bfqq->wr_coeff;
 	bool interactive = false;
 
-	bfq_log_bfqq(bfqd, bfqq, "add_request %d", rq_is_sync(rq));
+	bfq_log_bfqq(bfqd, bfqq, "add_request: size %u %s",
+		     blk_rq_sectors(rq), rq_is_sync(rq) ? "S" : "A");
+
+	if (bfqq->wr_coeff > 1) /* queue is being weight-raised */
+		bfq_log_bfqq(bfqd, bfqq,
+			"raising period dur %u/%u msec, old coeff %u, w %d(%d)",
+			jiffies_to_msecs(jiffies - bfqq->last_wr_start_finish),
+			jiffies_to_msecs(bfqq->wr_cur_max_time),
+			bfqq->wr_coeff,
+			bfqq->entity.weight, bfqq->entity.orig_weight);
+
 	bfqq->queued[rq_is_sync(rq)]++;
 	bfqd->queued++;
 
 	elv_rb_add(&bfqq->sort_list, rq);
 
 	/*
-	 * Check if this request is a better next-serve candidate.
+	 * Check if this request is a better next-to-serve candidate.
 	 */
 	prev = bfqq->next_rq;
 	next_rq = bfq_choose_req(bfqd, bfqq->next_rq, rq, bfqd->last_position);
@@ -887,160 +1379,10 @@ static void bfq_add_request(struct request *rq)
 	if (prev != bfqq->next_rq)
 		bfq_pos_tree_add_move(bfqd, bfqq);
 
-	if (!bfq_bfqq_busy(bfqq)) {
-		bool soft_rt, coop_or_in_burst,
-		     idle_for_long_time = time_is_before_jiffies(
-						bfqq->budget_timeout +
-						bfqd->bfq_wr_min_idle_time);
-
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
-		bfqg_stats_update_io_add(bfqq_group(RQ_BFQQ(rq)), bfqq,
-					 rq->cmd_flags);
-#endif
-		if (bfq_bfqq_sync(bfqq)) {
-			bool already_in_burst =
-			   !hlist_unhashed(&bfqq->burst_list_node) ||
-			   bfq_bfqq_in_large_burst(bfqq);
-			bfq_handle_burst(bfqd, bfqq, idle_for_long_time);
-			/*
-			 * If bfqq was not already in the current burst,
-			 * then, at this point, bfqq either has been
-			 * added to the current burst or has caused the
-			 * current burst to terminate. In particular, in
-			 * the second case, bfqq has become the first
-			 * queue in a possible new burst.
-			 * In both cases last_ins_in_burst needs to be
-			 * moved forward.
-			 */
-			if (!already_in_burst)
-				bfqd->last_ins_in_burst = jiffies;
-		}
-
-		coop_or_in_burst = bfq_bfqq_in_large_burst(bfqq) ||
-			bfq_bfqq_cooperations(bfqq) >= bfqd->bfq_coop_thresh;
-		soft_rt = bfqd->bfq_wr_max_softrt_rate > 0 &&
-			!coop_or_in_burst &&
-			time_is_before_jiffies(bfqq->soft_rt_next_start);
-		interactive = !coop_or_in_burst && idle_for_long_time;
-		entity->budget = max_t(unsigned long, bfqq->max_budget,
-				       bfq_serv_to_charge(next_rq, bfqq));
-
-		if (!bfq_bfqq_IO_bound(bfqq)) {
-			if (time_before(jiffies,
-					RQ_BIC(rq)->ttime.last_end_request +
-					bfqd->bfq_slice_idle)) {
-				bfqq->requests_within_timer++;
-				if (bfqq->requests_within_timer >=
-				    bfqd->bfq_requests_within_timer)
-					bfq_mark_bfqq_IO_bound(bfqq);
-			} else
-				bfqq->requests_within_timer = 0;
-		}
-
-		if (!bfqd->low_latency)
-			goto add_bfqq_busy;
-
-		if (bfq_bfqq_just_split(bfqq))
-			goto set_prio_changed;
-
-		/*
-		 * If the queue:
-		 * - is not being boosted,
-		 * - has been idle for enough time,
-		 * - is not a sync queue or is linked to a bfq_io_cq (it is
-		 *   shared "for its nature" or it is not shared and its
-		 *   requests have not been redirected to a shared queue)
-		 * start a weight-raising period.
-		 */
-		if (old_wr_coeff == 1 && (interactive || soft_rt) &&
-		    (!bfq_bfqq_sync(bfqq) || bfqq->bic)) {
-			bfqq->wr_coeff = bfqd->bfq_wr_coeff;
-			if (interactive)
-				bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
-			else
-				bfqq->wr_cur_max_time =
-					bfqd->bfq_wr_rt_max_time;
-			bfq_log_bfqq(bfqd, bfqq,
-				     "wrais starting at %lu, rais_max_time %u",
-				     jiffies,
-				     jiffies_to_msecs(bfqq->wr_cur_max_time));
-		} else if (old_wr_coeff > 1) {
-			if (interactive)
-				bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
-			else if (coop_or_in_burst ||
-				 (bfqq->wr_cur_max_time ==
-				  bfqd->bfq_wr_rt_max_time &&
-				  !soft_rt)) {
-				bfqq->wr_coeff = 1;
-				bfq_log_bfqq(bfqd, bfqq,
-					"wrais ending at %lu, rais_max_time %u",
-					jiffies,
-					jiffies_to_msecs(bfqq->
-						wr_cur_max_time));
-			} else if (time_before(
-					bfqq->last_wr_start_finish +
-					bfqq->wr_cur_max_time,
-					jiffies +
-					bfqd->bfq_wr_rt_max_time) &&
-				   soft_rt) {
-				/*
-				 *
-				 * The remaining weight-raising time is lower
-				 * than bfqd->bfq_wr_rt_max_time, which means
-				 * that the application is enjoying weight
-				 * raising either because deemed soft-rt in
-				 * the near past, or because deemed interactive
-				 * a long ago.
-				 * In both cases, resetting now the current
-				 * remaining weight-raising time for the
-				 * application to the weight-raising duration
-				 * for soft rt applications would not cause any
-				 * latency increase for the application (as the
-				 * new duration would be higher than the
-				 * remaining time).
-				 *
-				 * In addition, the application is now meeting
-				 * the requirements for being deemed soft rt.
-				 * In the end we can correctly and safely
-				 * (re)charge the weight-raising duration for
-				 * the application with the weight-raising
-				 * duration for soft rt applications.
-				 *
-				 * In particular, doing this recharge now, i.e.,
-				 * before the weight-raising period for the
-				 * application finishes, reduces the probability
-				 * of the following negative scenario:
-				 * 1) the weight of a soft rt application is
-				 *    raised at startup (as for any newly
-				 *    created application),
-				 * 2) since the application is not interactive,
-				 *    at a certain time weight-raising is
-				 *    stopped for the application,
-				 * 3) at that time the application happens to
-				 *    still have pending requests, and hence
-				 *    is destined to not have a chance to be
-				 *    deemed soft rt before these requests are
-				 *    completed (see the comments to the
-				 *    function bfq_bfqq_softrt_next_start()
-				 *    for details on soft rt detection),
-				 * 4) these pending requests experience a high
-				 *    latency because the application is not
-				 *    weight-raised while they are pending.
-				 */
-				bfqq->last_wr_start_finish = jiffies;
-				bfqq->wr_cur_max_time =
-					bfqd->bfq_wr_rt_max_time;
-			}
-		}
-set_prio_changed:
-		if (old_wr_coeff != bfqq->wr_coeff)
-			entity->prio_changed = 1;
-add_bfqq_busy:
-		bfqq->last_idle_bklogged = jiffies;
-		bfqq->service_from_backlogged = 0;
-		bfq_clear_bfqq_softrt_update(bfqq);
-		bfq_add_bfqq_busy(bfqd, bfqq);
-	} else {
+	if (!bfq_bfqq_busy(bfqq)) /* switching to busy ... */
+		bfq_bfqq_handle_idle_busy_switch(bfqd, bfqq, old_wr_coeff,
+						 rq, &interactive);
+	else {
 		if (bfqd->low_latency && old_wr_coeff == 1 && !rq_is_sync(rq) &&
 		    time_is_before_jiffies(
 				bfqq->last_wr_start_finish +
@@ -1049,16 +1391,43 @@ add_bfqq_busy:
 			bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
 
 			bfqd->wr_busy_queues++;
-			entity->prio_changed = 1;
+			bfqq->entity.prio_changed = 1;
 			bfq_log_bfqq(bfqd, bfqq,
-			    "non-idle wrais starting at %lu, rais_max_time %u",
-			    jiffies,
-			    jiffies_to_msecs(bfqq->wr_cur_max_time));
+				     "non-idle wrais starting, "
+				     "wr_max_time %u wr_busy %d",
+				     jiffies_to_msecs(bfqq->wr_cur_max_time),
+				     bfqd->wr_busy_queues);
 		}
 		if (prev != bfqq->next_rq)
 			bfq_updated_next_req(bfqd, bfqq);
 	}
 
+	/*
+	 * Assign jiffies to last_wr_start_finish in the following
+	 * cases:
+	 *
+	 * . if bfqq is not going to be weight-raised, because, for
+	 *   non weight-raised queues, last_wr_start_finish stores the
+	 *   arrival time of the last request; as of now, this piece
+	 *   of information is used only for deciding whether to
+	 *   weight-raise async queues
+	 *
+	 * . if bfqq is not weight-raised, because, if bfqq is now
+	 *   switching to weight-raised, then last_wr_start_finish
+	 *   stores the time when weight-raising starts
+	 *
+	 * . if bfqq is interactive, because, regardless of whether
+	 *   bfqq is currently weight-raised, the weight-raising
+	 *   period must start or restart (this case is considered
+	 *   separately because it is not detected by the above
+	 *   conditions, if bfqq is already weight-raised)
+	 *
+	 * last_wr_start_finish has to be updated also if bfqq is soft
+	 * real-time, because the weight-raising period is constantly
+	 * restarted on idle-to-busy transitions for these queues, but
+	 * this is already done in bfq_bfqq_handle_idle_busy_switch if
+	 * needed.
+	 */
 	if (bfqd->low_latency &&
 		(old_wr_coeff == 1 || bfqq->wr_coeff == 1 || interactive))
 		bfqq->last_wr_start_finish = jiffies;
@@ -1106,6 +1475,9 @@ static void bfq_remove_request(struct request *rq)
 	struct bfq_data *bfqd = bfqq->bfqd;
 	const int sync = rq_is_sync(rq);
 
+	BUG_ON(bfqq->entity.service > bfqq->entity.budget &&
+	       bfqq == bfqd->in_service_queue);
+
 	if (bfqq->next_rq == rq) {
 		bfqq->next_rq = bfq_find_next_rq(bfqd, bfqq, rq);
 		bfq_updated_next_req(bfqd, bfqq);
@@ -1119,8 +1491,25 @@ static void bfq_remove_request(struct request *rq)
 	elv_rb_del(&bfqq->sort_list, rq);
 
 	if (RB_EMPTY_ROOT(&bfqq->sort_list)) {
-		if (bfq_bfqq_busy(bfqq) && bfqq != bfqd->in_service_queue)
+		BUG_ON(bfqq->entity.budget < 0);
+
+		if (bfq_bfqq_busy(bfqq) && bfqq != bfqd->in_service_queue) {
 			bfq_del_bfqq_busy(bfqd, bfqq, 1);
+
+			/* bfqq emptied. In normal operation, when
+			 * bfqq is empty, bfqq->entity.service and
+			 * bfqq->entity.budget must contain,
+			 * respectively, the service received and the
+			 * budget used last time bfqq emptied. These
+			 * facts do not hold in this case, as at least
+			 * this last removal occurred while bfqq is
+			 * not in service. To avoid inconsistencies,
+			 * reset both bfqq->entity.service and
+			 * bfqq->entity.budget.
+			 */
+			bfqq->entity.budget = bfqq->entity.service = 0;
+		}
+
 		/*
 		 * Remove queue from request-position tree as it is empty.
 		 */
@@ -1134,9 +1523,7 @@ static void bfq_remove_request(struct request *rq)
 		BUG_ON(bfqq->meta_pending == 0);
 		bfqq->meta_pending--;
 	}
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
 	bfqg_stats_update_io_remove(bfqq_group(bfqq), rq->cmd_flags);
-#endif
 }
 
 static int bfq_merge(struct request_queue *q, struct request **req,
@@ -1221,21 +1608,25 @@ static void bfq_merged_requests(struct request_queue *q, struct request *rq,
 		bfqq->next_rq = rq;
 
 	bfq_remove_request(next);
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
 	bfqg_stats_update_io_merged(bfqq_group(bfqq), next->cmd_flags);
-#endif
 }
 
 /* Must be called with bfqq != NULL */
 static void bfq_bfqq_end_wr(struct bfq_queue *bfqq)
 {
 	BUG_ON(!bfqq);
+
 	if (bfq_bfqq_busy(bfqq))
 		bfqq->bfqd->wr_busy_queues--;
 	bfqq->wr_coeff = 1;
 	bfqq->wr_cur_max_time = 0;
-	/* Trigger a weight change on the next activation of the queue */
+	/*
+	 * Trigger a weight change on the next invocation of
+	 * __bfq_entity_update_weight_prio.
+	 */
 	bfqq->entity.prio_changed = 1;
+	bfq_log_bfqq(bfqq->bfqd, bfqq, "end_wr: wr_busy %d",
+		     bfqq->bfqd->wr_busy_queues);
 }
 
 static void bfq_end_wr_async_queues(struct bfq_data *bfqd,
@@ -1278,7 +1669,7 @@ static int bfq_rq_close_to_sector(void *io_struct, bool request,
 				  sector_t sector)
 {
 	return abs(bfq_io_struct_pos(io_struct, request) - sector) <=
-	       BFQQ_SEEK_THR;
+	       BFQQ_CLOSE_THR;
 }
 
 static struct bfq_queue *bfqq_find_close(struct bfq_data *bfqd,
@@ -1400,7 +1791,7 @@ bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
 	 * throughput.
 	 */
 	bfqq->new_bfqq = new_bfqq;
-	atomic_add(process_refs, &new_bfqq->ref);
+	new_bfqq->ref += process_refs;
 	return new_bfqq;
 }
 
@@ -1431,9 +1822,23 @@ static bool bfq_may_be_close_cooperator(struct bfq_queue *bfqq,
 }
 
 /*
- * Attempt to schedule a merge of bfqq with the currently in-service queue
- * or with a close queue among the scheduled queues.
- * Return NULL if no merge was scheduled, a pointer to the shared bfq_queue
+ * If this function returns true, then bfqq cannot be merged. The idea
+ * is that true cooperation happens very early after processes start
+ * to do I/O. Usually, late cooperations are just accidental false
+ * positives. In case bfqq is weight-raised, such false positives
+ * would evidently degrade latency guarantees for bfqq.
+ */
+bool wr_from_too_long(struct bfq_queue *bfqq)
+{
+	return bfqq->wr_coeff > 1 &&
+		time_is_before_jiffies(bfqq->last_wr_start_finish +
+				       msecs_to_jiffies(100));
+}
+
+/*
+ * Attempt to schedule a merge of bfqq with the currently in-service
+ * queue or with a close queue among the scheduled queues.  Return
+ * NULL if no merge was scheduled, a pointer to the shared bfq_queue
  * structure otherwise.
  *
  * The OOM queue is not allowed to participate to cooperation: in fact, since
@@ -1442,6 +1847,18 @@ static bool bfq_may_be_close_cooperator(struct bfq_queue *bfqq,
  * handle merging with the OOM queue would be quite complex and expensive
  * to maintain. Besides, in such a critical condition as an out of memory,
  * the benefits of queue merging may be little relevant, or even negligible.
+ *
+ * Weight-raised queues can be merged only if their weight-raising
+ * period has just started. In fact cooperating processes are usually
+ * started together. Thus, with this filter we avoid false positives
+ * that would jeopardize low-latency guarantees.
+ *
+ * WARNING: queue merging may impair fairness among non-weight raised
+ * queues, for at least two reasons: 1) the original weight of a
+ * merged queue may change during the merged state, 2) even being the
+ * weight the same, a merged queue may be bloated with many more
+ * requests than the ones produced by its originally-associated
+ * process.
  */
 static struct bfq_queue *
 bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
@@ -1451,16 +1868,32 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 
 	if (bfqq->new_bfqq)
 		return bfqq->new_bfqq;
-	if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq))
+
+	if (io_struct && wr_from_too_long(bfqq) &&
+	    likely(bfqq != &bfqd->oom_bfqq))
+		bfq_log_bfqq(bfqd, bfqq,
+			     "would have looked for coop, but bfq%d wr",
+			bfqq->pid);
+
+	if (!io_struct ||
+	    wr_from_too_long(bfqq) ||
+	    unlikely(bfqq == &bfqd->oom_bfqq))
 		return NULL;
-	/* If device has only one backlogged bfq_queue, don't search. */
+
+	/* If there is only one backlogged queue, don't search. */
 	if (bfqd->busy_queues == 1)
 		return NULL;
 
 	in_service_bfqq = bfqd->in_service_queue;
 
+	if (in_service_bfqq && in_service_bfqq != bfqq &&
+	    bfqd->in_service_bic && wr_from_too_long(in_service_bfqq)
+	    && likely(in_service_bfqq == &bfqd->oom_bfqq))
+		bfq_log_bfqq(bfqd, bfqq,
+		"would have tried merge with in-service-queue, but wr");
+
 	if (!in_service_bfqq || in_service_bfqq == bfqq ||
-	    !bfqd->in_service_bic ||
+	    !bfqd->in_service_bic || wr_from_too_long(in_service_bfqq) ||
 	    unlikely(in_service_bfqq == &bfqd->oom_bfqq))
 		goto check_scheduled;
 
@@ -1482,7 +1915,15 @@ check_scheduled:
 
 	BUG_ON(new_bfqq && bfqq->entity.parent != new_bfqq->entity.parent);
 
-	if (new_bfqq && likely(new_bfqq != &bfqd->oom_bfqq) &&
+	if (new_bfqq && wr_from_too_long(new_bfqq) &&
+	    likely(new_bfqq != &bfqd->oom_bfqq) &&
+	    bfq_may_be_close_cooperator(bfqq, new_bfqq))
+		bfq_log_bfqq(bfqd, bfqq,
+			     "would have merged with bfq%d, but wr",
+			     new_bfqq->pid);
+
+	if (new_bfqq && !wr_from_too_long(new_bfqq) &&
+	    likely(new_bfqq != &bfqd->oom_bfqq) &&
 	    bfq_may_be_close_cooperator(bfqq, new_bfqq))
 		return bfq_setup_merge(bfqq, new_bfqq);
 
@@ -1498,46 +1939,11 @@ static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
 	 */
 	if (!bfqq->bic)
 		return;
-	if (bfqq->bic->wr_time_left)
-		/*
-		 * This is the queue of a just-started process, and would
-		 * deserve weight raising: we set wr_time_left to the full
-		 * weight-raising duration to trigger weight-raising when
-		 * and if the queue is split and the first request of the
-		 * queue is enqueued.
-		 */
-		bfqq->bic->wr_time_left = bfq_wr_duration(bfqq->bfqd);
-	else if (bfqq->wr_coeff > 1) {
-		unsigned long wr_duration =
-			jiffies - bfqq->last_wr_start_finish;
-		/*
-		 * It may happen that a queue's weight raising period lasts
-		 * longer than its wr_cur_max_time, as weight raising is
-		 * handled only when a request is enqueued or dispatched (it
-		 * does not use any timer). If the weight raising period is
-		 * about to end, don't save it.
-		 */
-		if (bfqq->wr_cur_max_time <= wr_duration)
-			bfqq->bic->wr_time_left = 0;
-		else
-			bfqq->bic->wr_time_left =
-				bfqq->wr_cur_max_time - wr_duration;
-		/*
-		 * The bfq_queue is becoming shared or the requests of the
-		 * process owning the queue are being redirected to a shared
-		 * queue. Stop the weight raising period of the queue, as in
-		 * both cases it should not be owned by an interactive or
-		 * soft real-time application.
-		 */
-		bfq_bfqq_end_wr(bfqq);
-	} else
-		bfqq->bic->wr_time_left = 0;
+
 	bfqq->bic->saved_idle_window = bfq_bfqq_idle_window(bfqq);
 	bfqq->bic->saved_IO_bound = bfq_bfqq_IO_bound(bfqq);
 	bfqq->bic->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq);
 	bfqq->bic->was_in_burst_list = !hlist_unhashed(&bfqq->burst_list_node);
-	bfqq->bic->cooperations++;
-	bfqq->bic->failed_cooperations = 0;
 }
 
 static void bfq_get_bic_reference(struct bfq_queue *bfqq)
@@ -1562,6 +1968,40 @@ bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic,
 	if (bfq_bfqq_IO_bound(bfqq))
 		bfq_mark_bfqq_IO_bound(new_bfqq);
 	bfq_clear_bfqq_IO_bound(bfqq);
+
+	/*
+	 * If bfqq is weight-raised, then let new_bfqq inherit
+	 * weight-raising. To reduce false positives, neglect the case
+	 * where bfqq has just been created, but has not yet made it
+	 * to be weight-raised (which may happen because EQM may merge
+	 * bfqq even before bfq_add_request is executed for the first
+	 * time for bfqq). Handling this case would however be very
+	 * easy, thanks to the flag just_created.
+	 */
+	if (new_bfqq->wr_coeff == 1 && bfqq->wr_coeff > 1) {
+		new_bfqq->wr_coeff = bfqq->wr_coeff;
+		new_bfqq->wr_cur_max_time = bfqq->wr_cur_max_time;
+		new_bfqq->last_wr_start_finish = bfqq->last_wr_start_finish;
+		if (bfq_bfqq_busy(new_bfqq))
+		    bfqd->wr_busy_queues++;
+		new_bfqq->entity.prio_changed = 1;
+		bfq_log_bfqq(bfqd, new_bfqq,
+			     "wr starting after merge with %d, "
+			     "rais_max_time %u",
+			     bfqq->pid,
+			     jiffies_to_msecs(bfqq->wr_cur_max_time));
+	}
+
+	if (bfqq->wr_coeff > 1) { /* bfqq has given its wr to new_bfqq */
+		bfqq->wr_coeff = 1;
+		bfqq->entity.prio_changed = 1;
+		if (bfq_bfqq_busy(bfqq))
+			bfqd->wr_busy_queues--;
+	}
+
+	bfq_log_bfqq(bfqd, new_bfqq, "merge_bfqqs: wr_busy %d",
+		     bfqd->wr_busy_queues);
+
 	/*
 	 * Grab a reference to the bic, to prevent it from being destroyed
 	 * before being possibly touched by a bfq_split_bfqq().
@@ -1588,18 +2028,6 @@ bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic,
 	bfq_put_queue(bfqq);
 }
 
-static void bfq_bfqq_increase_failed_cooperations(struct bfq_queue *bfqq)
-{
-	struct bfq_io_cq *bic = bfqq->bic;
-	struct bfq_data *bfqd = bfqq->bfqd;
-
-	if (bic && bfq_bfqq_cooperations(bfqq) >= bfqd->bfq_coop_thresh) {
-		bic->failed_cooperations++;
-		if (bic->failed_cooperations >= bfqd->bfq_failed_cooperations)
-			bic->cooperations = 0;
-	}
-}
-
 static int bfq_allow_merge(struct request_queue *q, struct request *rq,
 			   struct bio *bio)
 {
@@ -1637,30 +2065,86 @@ static int bfq_allow_merge(struct request_queue *q, struct request *rq,
 			 * to decide whether bio and rq can be merged.
 			 */
 			bfqq = new_bfqq;
-		} else
-			bfq_bfqq_increase_failed_cooperations(bfqq);
+		}
 	}
 
 	return bfqq == RQ_BFQQ(rq);
 }
 
+/*
+ * Set the maximum time for the in-service queue to consume its
+ * budget. This prevents seeky processes from lowering the throughput.
+ * In practice, a time-slice service scheme is used with seeky
+ * processes.
+ */
+static void bfq_set_budget_timeout(struct bfq_data *bfqd,
+				   struct bfq_queue *bfqq)
+{
+	unsigned int timeout_coeff;
+	if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time)
+		timeout_coeff = 1;
+	else
+		timeout_coeff = bfqq->entity.weight / bfqq->entity.orig_weight;
+
+	bfqd->last_budget_start = ktime_get();
+
+	bfqq->budget_timeout = jiffies +
+		bfqd->bfq_timeout * timeout_coeff;
+
+	bfq_log_bfqq(bfqd, bfqq, "set budget_timeout %u",
+		jiffies_to_msecs(bfqd->bfq_timeout * timeout_coeff));
+}
+
 static void __bfq_set_in_service_queue(struct bfq_data *bfqd,
 				       struct bfq_queue *bfqq)
 {
 	if (bfqq) {
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
 		bfqg_stats_update_avg_queue_size(bfqq_group(bfqq));
-#endif
 		bfq_mark_bfqq_must_alloc(bfqq);
-		bfq_mark_bfqq_budget_new(bfqq);
 		bfq_clear_bfqq_fifo_expire(bfqq);
 
 		bfqd->budgets_assigned = (bfqd->budgets_assigned*7 + 256) / 8;
 
+		BUG_ON(bfqq == bfqd->in_service_queue);
+		BUG_ON(RB_EMPTY_ROOT(&bfqq->sort_list));
+
+		if (bfqq->wr_coeff > 1 &&
+		    bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
+			time_is_before_jiffies(bfqq->budget_timeout)) {
+			/*
+			 * For soft real-time queues, move the start
+			 * of the weight-raising period forward by the
+			 * time the queue has not received any
+			 * service. Otherwise, a relatively long
+			 * service delay is likely to cause the
+			 * weight-raising period of the queue to end,
+			 * because of the short duration of the
+			 * weight-raising period of a soft real-time
+			 * queue.  It is worth noting that this move
+			 * is not so dangerous for the other queues,
+			 * because soft real-time queues are not
+			 * greedy.
+			 *
+			 * To not add a further variable, we use the
+			 * overloaded field budget_timeout to
+			 * determine for how long the queue has not
+			 * received service, i.e., how much time has
+			 * elapsed since the queue expired. However,
+			 * this is a little imprecise, because
+			 * budget_timeout is set to jiffies if bfqq
+			 * not only expires, but also remains with no
+			 * request.
+			 */
+			bfqq->last_wr_start_finish += jiffies -
+				bfqq->budget_timeout;
+		}
+
+		bfq_set_budget_timeout(bfqd, bfqq);
 		bfq_log_bfqq(bfqd, bfqq,
 			     "set_in_service_queue, cur-budget = %d",
 			     bfqq->entity.budget);
-	}
+	} else
+		bfq_log(bfqd, "set_in_service_queue: NULL");
 
 	bfqd->in_service_queue = bfqq;
 }
@@ -1676,31 +2160,6 @@ static struct bfq_queue *bfq_set_in_service_queue(struct bfq_data *bfqd)
 	return bfqq;
 }
 
-/*
- * If enough samples have been computed, return the current max budget
- * stored in bfqd, which is dynamically updated according to the
- * estimated disk peak rate; otherwise return the default max budget
- */
-static int bfq_max_budget(struct bfq_data *bfqd)
-{
-	if (bfqd->budgets_assigned < bfq_stats_min_budgets)
-		return bfq_default_max_budget;
-	else
-		return bfqd->bfq_max_budget;
-}
-
-/*
- * Return min budget, which is a fraction of the current or default
- * max budget (trying with 1/32)
- */
-static int bfq_min_budget(struct bfq_data *bfqd)
-{
-	if (bfqd->budgets_assigned < bfq_stats_min_budgets)
-		return bfq_default_max_budget / 32;
-	else
-		return bfqd->bfq_max_budget / 32;
-}
-
 static void bfq_arm_slice_timer(struct bfq_data *bfqd)
 {
 	struct bfq_queue *bfqq = bfqd->in_service_queue;
@@ -1729,58 +2188,30 @@ static void bfq_arm_slice_timer(struct bfq_data *bfqd)
 	sl = bfqd->bfq_slice_idle;
 	/*
 	 * Unless the queue is being weight-raised or the scenario is
-	 * asymmetric, grant only minimum idle time if the queue either
-	 * has been seeky for long enough or has already proved to be
-	 * constantly seeky.
+	 * asymmetric, grant only minimum idle time if the queue
+	 * is seeky. A long idling is preserved for a weight-raised
+	 * queue, or, more in general, in an asymemtric scenario,
+	 * because a long idling is needed for guaranteeing to a queue
+	 * its reserved share of the throughput (in particular, it is
+	 * needed if the queue has a higher weight than some other
+	 * queue).
 	 */
-	if (bfq_sample_valid(bfqq->seek_samples) &&
-	    ((BFQQ_SEEKY(bfqq) && bfqq->entity.service >
-				  bfq_max_budget(bfqq->bfqd) / 8) ||
-	      bfq_bfqq_constantly_seeky(bfqq)) && bfqq->wr_coeff == 1 &&
+	if (BFQQ_SEEKY(bfqq) && bfqq->wr_coeff == 1 &&
 	    bfq_symmetric_scenario(bfqd))
 		sl = min(sl, msecs_to_jiffies(BFQ_MIN_TT));
-	else if (bfqq->wr_coeff > 1)
-		sl = sl * 3;
+
 	bfqd->last_idling_start = ktime_get();
 	mod_timer(&bfqd->idle_slice_timer, jiffies + sl);
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
 	bfqg_stats_set_start_idle_time(bfqq_group(bfqq));
-#endif
 	bfq_log(bfqd, "arm idle: %u/%u ms",
 		jiffies_to_msecs(sl), jiffies_to_msecs(bfqd->bfq_slice_idle));
 }
 
 /*
- * Set the maximum time for the in-service queue to consume its
- * budget. This prevents seeky processes from lowering the disk
- * throughput (always guaranteed with a time slice scheme as in CFQ).
- */
-static void bfq_set_budget_timeout(struct bfq_data *bfqd)
-{
-	struct bfq_queue *bfqq = bfqd->in_service_queue;
-	unsigned int timeout_coeff;
-	if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time)
-		timeout_coeff = 1;
-	else
-		timeout_coeff = bfqq->entity.weight / bfqq->entity.orig_weight;
-
-	bfqd->last_budget_start = ktime_get();
-
-	bfq_clear_bfqq_budget_new(bfqq);
-	bfqq->budget_timeout = jiffies +
-		bfqd->bfq_timeout[bfq_bfqq_sync(bfqq)] * timeout_coeff;
-
-	bfq_log_bfqq(bfqd, bfqq, "set budget_timeout %u",
-		jiffies_to_msecs(bfqd->bfq_timeout[bfq_bfqq_sync(bfqq)] *
-		timeout_coeff));
-}
-
-/*
- * Move request from internal lists to the request queue dispatch list.
+ * Move request from internal lists to the dispatch list of the request queue
  */
 static void bfq_dispatch_insert(struct request_queue *q, struct request *rq)
 {
-	struct bfq_data *bfqd = q->elevator->elevator_data;
 	struct bfq_queue *bfqq = RQ_BFQQ(rq);
 
 	/*
@@ -1794,15 +2225,9 @@ static void bfq_dispatch_insert(struct request_queue *q, struct request *rq)
 	 * incrementing bfqq->dispatched.
 	 */
 	bfqq->dispatched++;
+
 	bfq_remove_request(rq);
 	elv_dispatch_sort(q, rq);
-
-	if (bfq_bfqq_sync(bfqq))
-		bfqd->sync_flight++;
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
-	bfqg_stats_update_dispatch(bfqq_group(bfqq), blk_rq_bytes(rq),
-				   rq->cmd_flags);
-#endif
 }
 
 /*
@@ -1822,18 +2247,12 @@ static struct request *bfq_check_fifo(struct bfq_queue *bfqq)
 
 	rq = rq_entry_fifo(bfqq->fifo.next);
 
-	if (time_before(jiffies, rq->fifo_time))
+	if (time_is_after_jiffies(rq->fifo_time))
 		return NULL;
 
 	return rq;
 }
 
-static int bfq_bfqq_budget_left(struct bfq_queue *bfqq)
-{
-	struct bfq_entity *entity = &bfqq->entity;
-	return entity->budget - entity->service;
-}
-
 static void __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq)
 {
 	BUG_ON(bfqq != bfqd->in_service_queue);
@@ -1850,12 +2269,15 @@ static void __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq)
 		bfq_mark_bfqq_split_coop(bfqq);
 
 	if (RB_EMPTY_ROOT(&bfqq->sort_list)) {
-		/*
-		 * Overloading budget_timeout field to store the time
-		 * at which the queue remains with no backlog; used by
-		 * the weight-raising mechanism.
-		 */
-		bfqq->budget_timeout = jiffies;
+		if (bfqq->dispatched == 0)
+			/*
+			 * Overloading budget_timeout field to store
+			 * the time at which the queue remains with no
+			 * backlog and no outstanding request; used by
+			 * the weight-raising mechanism.
+			 */
+			bfqq->budget_timeout = jiffies;
+
 		bfq_del_bfqq_busy(bfqd, bfqq, 1);
 	} else {
 		bfq_activate_bfqq(bfqd, bfqq);
@@ -1882,10 +2304,19 @@ static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd,
 	struct request *next_rq;
 	int budget, min_budget;
 
-	budget = bfqq->max_budget;
+	BUG_ON(bfqq != bfqd->in_service_queue);
+
 	min_budget = bfq_min_budget(bfqd);
 
-	BUG_ON(bfqq != bfqd->in_service_queue);
+	if (bfqq->wr_coeff == 1)
+		budget = bfqq->max_budget;
+	else /*
+	      * Use a constant, low budget for weight-raised queues,
+	      * to help achieve a low latency. Keep it slightly higher
+	      * than the minimum possible budget, to cause a little
+	      * bit fewer expirations.
+	      */
+		budget = 2 * min_budget;
 
 	bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last budg %d, budg left %d",
 		bfqq->entity.budget, bfq_bfqq_budget_left(bfqq));
@@ -1894,7 +2325,7 @@ static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd,
 	bfq_log_bfqq(bfqd, bfqq, "recalc_budg: sync %d, seeky %d",
 		bfq_bfqq_sync(bfqq), BFQQ_SEEKY(bfqd->in_service_queue));
 
-	if (bfq_bfqq_sync(bfqq)) {
+	if (bfq_bfqq_sync(bfqq) && bfqq->wr_coeff == 1) {
 		switch (reason) {
 		/*
 		 * Caveat: in all the following cases we trade latency
@@ -1936,14 +2367,10 @@ static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd,
 			break;
 		case BFQ_BFQQ_BUDGET_TIMEOUT:
 			/*
-			 * We double the budget here because: 1) it
-			 * gives the chance to boost the throughput if
-			 * this is not a seeky process (which may have
-			 * bumped into this timeout because of, e.g.,
-			 * ZBR), 2) together with charge_full_budget
-			 * it helps give seeky processes higher
-			 * timestamps, and hence be served less
-			 * frequently.
+			 * We double the budget here because it gives
+			 * the chance to boost the throughput if this
+			 * is not a seeky process (and has bumped into
+			 * this timeout because of, e.g., ZBR).
 			 */
 			budget = min(budget * 2, bfqd->bfq_max_budget);
 			break;
@@ -1960,17 +2387,49 @@ static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd,
 			budget = min(budget * 4, bfqd->bfq_max_budget);
 			break;
 		case BFQ_BFQQ_NO_MORE_REQUESTS:
-		       /*
-			* Leave the budget unchanged.
-			*/
+			/*
+			 * For queues that expire for this reason, it
+			 * is particularly important to keep the
+			 * budget close to the actual service they
+			 * need. Doing so reduces the timestamp
+			 * misalignment problem described in the
+			 * comments in the body of
+			 * __bfq_activate_entity. In fact, suppose
+			 * that a queue systematically expires for
+			 * BFQ_BFQQ_NO_MORE_REQUESTS and presents a
+			 * new request in time to enjoy timestamp
+			 * back-shifting. The larger the budget of the
+			 * queue is with respect to the service the
+			 * queue actually requests in each service
+			 * slot, the more times the queue can be
+			 * reactivated with the same virtual finish
+			 * time. It follows that, even if this finish
+			 * time is pushed to the system virtual time
+			 * to reduce the consequent timestamp
+			 * misalignment, the queue unjustly enjoys for
+			 * many re-activations a lower finish time
+			 * than all newly activated queues.
+			 *
+			 * The service needed by bfqq is measured
+			 * quite precisely by bfqq->entity.service.
+			 * Since bfqq does not enjoy device idling,
+			 * bfqq->entity.service is equal to the number
+			 * of sectors that the process associated with
+			 * bfqq requested to read/write before waiting
+			 * for request completions, or blocking for
+			 * other reasons.
+			 */
+			budget = max_t(int, bfqq->entity.service, min_budget);
+			break;
 		default:
 			return;
 		}
-	} else
+	} else if (!bfq_bfqq_sync(bfqq))
 		/*
-		 * Async queues get always the maximum possible budget
-		 * (their ability to dispatch is limited by
-		 * @bfqd->bfq_max_budget_async_rq).
+		 * Async queues get always the maximum possible
+		 * budget, as for them we do not care about latency
+		 * (in addition, their ability to dispatch is limited
+		 * by the charging factor).
 		 */
 		budget = bfqd->bfq_max_budget;
 
@@ -1981,65 +2440,105 @@ static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd,
 		bfqq->max_budget = min(bfqq->max_budget, bfqd->bfq_max_budget);
 
 	/*
-	 * Make sure that we have enough budget for the next request.
-	 * Since the finish time of the bfqq must be kept in sync with
-	 * the budget, be sure to call __bfq_bfqq_expire() after the
+	 * If there is still backlog, then assign a new budget, making
+	 * sure that it is large enough for the next request.  Since
+	 * the finish time of bfqq must be kept in sync with the
+	 * budget, be sure to call __bfq_bfqq_expire() *after* this
 	 * update.
+	 *
+	 * If there is no backlog, then no need to update the budget;
+	 * it will be updated on the arrival of a new request.
 	 */
 	next_rq = bfqq->next_rq;
-	if (next_rq)
+	if (next_rq) {
+		BUG_ON(reason == BFQ_BFQQ_TOO_IDLE ||
+		       reason == BFQ_BFQQ_NO_MORE_REQUESTS);
 		bfqq->entity.budget = max_t(unsigned long, bfqq->max_budget,
 					    bfq_serv_to_charge(next_rq, bfqq));
-	else
-		bfqq->entity.budget = bfqq->max_budget;
+		BUG_ON(!bfq_bfqq_busy(bfqq));
+		BUG_ON(RB_EMPTY_ROOT(&bfqq->sort_list));
+	}
 
 	bfq_log_bfqq(bfqd, bfqq, "head sect: %u, new budget %d",
 			next_rq ? blk_rq_sectors(next_rq) : 0,
 			bfqq->entity.budget);
 }
 
-static unsigned long bfq_calc_max_budget(u64 peak_rate, u64 timeout)
+static unsigned long bfq_calc_max_budget(struct bfq_data *bfqd)
 {
-	unsigned long max_budget;
-
 	/*
 	 * The max_budget calculated when autotuning is equal to the
-	 * amount of sectors transfered in timeout_sync at the
+	 * amount of sectors transfered in timeout at the
 	 * estimated peak rate.
 	 */
-	max_budget = (unsigned long)(peak_rate * 1000 *
-				     timeout >> BFQ_RATE_SHIFT);
-
-	return max_budget;
+	return bfqd->peak_rate * 1000 * jiffies_to_msecs(bfqd->bfq_timeout) >>
+		BFQ_RATE_SHIFT;
 }
 
 /*
- * In addition to updating the peak rate, checks whether the process
- * is "slow", and returns 1 if so. This slow flag is used, in addition
- * to the budget timeout, to reduce the amount of service provided to
- * seeky processes, and hence reduce their chances to lower the
- * throughput. See the code for more details.
+ * Update the read peak rate (quantity used for auto-tuning) as a
+ * function of the rate at which bfqq has been served, and check
+ * whether the process associated with bfqq is "slow". Return true if
+ * the process is slow. The slow flag is used, in addition to the
+ * budget timeout, to reduce the amount of service provided to seeky
+ * processes, and hence reduce their chances to lower the
+ * throughput. More details in the body of the function.
+ *
+ * An important observation is in order: with devices with internal
+ * queues, it is hard if ever possible to know when and for how long
+ * an I/O request is processed by the device (apart from the trivial
+ * I/O pattern where a new request is dispatched only after the
+ * previous one has been completed). This makes it hard to evaluate
+ * the real rate at which the I/O requests of each bfq_queue are
+ * served.  In fact, for an I/O scheduler like BFQ, serving a
+ * bfq_queue means just dispatching its requests during its service
+ * slot, i.e., until the budget of the queue is exhausted, or the
+ * queue remains idle, or, finally, a timeout fires. But, during the
+ * service slot of a bfq_queue, the device may be still processing
+ * requests of bfq_queues served in previous service slots. On the
+ * opposite end, the requests of the in-service bfq_queue may be
+ * completed after the service slot of the queue finishes. Anyway,
+ * unless more sophisticated solutions are used (where possible), the
+ * sum of the sizes of the requests dispatched during the service slot
+ * of a bfq_queue is probably the only approximation available for
+ * the service received by the bfq_queue during its service slot. And,
+ * as written above, this sum is the quantity used in this function to
+ * evaluate the peak rate.
  */
 static bool bfq_update_peak_rate(struct bfq_data *bfqd, struct bfq_queue *bfqq,
-				 bool compensate, enum bfqq_expiration reason)
+				 bool compensate, enum bfqq_expiration reason,
+				 unsigned long *delta_ms)
 {
-	u64 bw, usecs, expected, timeout;
-	ktime_t delta;
+	u64 bw, bwdiv10, delta_usecs, delta_ms_tmp;
+	ktime_t delta_ktime;
 	int update = 0;
+	bool slow = BFQQ_SEEKY(bfqq); /* if delta too short, use seekyness */
 
-	if (!bfq_bfqq_sync(bfqq) || bfq_bfqq_budget_new(bfqq))
+	if (!bfq_bfqq_sync(bfqq))
 		return false;
 
 	if (compensate)
-		delta = bfqd->last_idling_start;
+		delta_ktime = bfqd->last_idling_start;
 	else
-		delta = ktime_get();
-	delta = ktime_sub(delta, bfqd->last_budget_start);
-	usecs = ktime_to_us(delta);
+		delta_ktime = ktime_get();
+	delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
+	delta_usecs = ktime_to_us(delta_ktime);
 
 	/* Don't trust short/unrealistic values. */
-	if (usecs < 100 || usecs >= LONG_MAX)
-		return false;
+	if (delta_usecs < 1000 || delta_usecs >= LONG_MAX) {
+		if (blk_queue_nonrot(bfqd->queue))
+			*delta_ms = BFQ_MIN_TT; /* give same worst-case
+						   guarantees as
+						   idling for seeky
+						*/
+		else /* Charge at least one seek */
+			*delta_ms = jiffies_to_msecs(bfq_slice_idle);
+		return slow;
+	}
+
+	delta_ms_tmp = delta_usecs;
+	do_div(delta_ms_tmp, 1000);
+	*delta_ms = delta_ms_tmp;
 
 	/*
 	 * Calculate the bandwidth for the last slice.  We use a 64 bit
@@ -2048,32 +2547,51 @@ static bool bfq_update_peak_rate(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 	 * and to avoid overflows.
 	 */
 	bw = (u64)bfqq->entity.service << BFQ_RATE_SHIFT;
-	do_div(bw, (unsigned long)usecs);
-
-	timeout = jiffies_to_msecs(bfqd->bfq_timeout[BLK_RW_SYNC]);
+	do_div(bw, (unsigned long)delta_usecs);
 
+	bfq_log(bfqd, "measured bw = %llu sects/sec",
+		(1000000*bw)>>BFQ_RATE_SHIFT);
 	/*
 	 * Use only long (> 20ms) intervals to filter out spikes for
 	 * the peak rate estimation.
 	 */
-	if (usecs > 20000) {
+	if (delta_usecs > 20000) {
+		bool fully_sequential = bfqq->seek_history == 0;
+		/*
+		 * Soft real-time queues are not good candidates for
+		 * evaluating bw, as they are likely to be slow even
+		 * if sequential.
+		 */
+		bool non_soft_rt = bfqq->wr_coeff == 1 ||
+			bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time;
+		bool consumed_large_budget =
+			reason == BFQ_BFQQ_BUDGET_EXHAUSTED &&
+			bfqq->entity.budget >= bfqd->bfq_max_budget * 2 / 3;
+		bool served_for_long_time =
+			reason == BFQ_BFQQ_BUDGET_TIMEOUT ||
+			consumed_large_budget;
+
+		BUG_ON(bfqq->seek_history == 0 &&
+		       hweight32(bfqq->seek_history) != 0);
+
 		if (bw > bfqd->peak_rate ||
-		   (!BFQQ_SEEKY(bfqq) &&
-		    reason == BFQ_BFQQ_BUDGET_TIMEOUT)) {
-			bfq_log(bfqd, "measured bw =%llu", bw);
+		    (bfq_bfqq_sync(bfqq) && fully_sequential && non_soft_rt &&
+		     served_for_long_time)) {
 			/*
 			 * To smooth oscillations use a low-pass filter with
-			 * alpha=7/8, i.e.,
-			 * new_rate = (7/8) * old_rate + (1/8) * bw
+			 * alpha=9/10, i.e.,
+			 * new_rate = (9/10) * old_rate + (1/10) * bw
 			 */
-			do_div(bw, 8);
-			if (bw == 0)
-				return 0;
-			bfqd->peak_rate *= 7;
-			do_div(bfqd->peak_rate, 8);
-			bfqd->peak_rate += bw;
+			bwdiv10 = bw;
+			do_div(bwdiv10, 10);
+			if (bwdiv10 == 0)
+				return false; /* bw too low to be used */
+			bfqd->peak_rate *= 9;
+			do_div(bfqd->peak_rate, 10);
+			bfqd->peak_rate += bwdiv10;
 			update = 1;
-			bfq_log(bfqd, "new peak_rate=%llu", bfqd->peak_rate);
+			bfq_log(bfqd, "new peak_rate = %llu sects/sec",
+				(1000000*bfqd->peak_rate)>>BFQ_RATE_SHIFT);
 		}
 
 		update |= bfqd->peak_rate_samples == BFQ_PEAK_RATE_SAMPLES - 1;
@@ -2086,9 +2604,8 @@ static bool bfq_update_peak_rate(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 			int dev_type = blk_queue_nonrot(bfqd->queue);
 			if (bfqd->bfq_user_max_budget == 0) {
 				bfqd->bfq_max_budget =
-					bfq_calc_max_budget(bfqd->peak_rate,
-							    timeout);
-				bfq_log(bfqd, "new max_budget=%d",
+					bfq_calc_max_budget(bfqd);
+				bfq_log(bfqd, "new max_budget = %d",
 					bfqd->bfq_max_budget);
 			}
 			if (bfqd->device_speed == BFQ_BFQD_FAST &&
@@ -2102,38 +2619,35 @@ static bool bfq_update_peak_rate(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 				bfqd->RT_prod = R_fast[dev_type] *
 						T_fast[dev_type];
 			}
+			bfq_log(bfqd, "dev_speed_class = %d (%d sects/sec), "
+				"thresh %d setcs/sec",
+				bfqd->device_speed,
+				bfqd->device_speed == BFQ_BFQD_FAST ?
+				(1000000*R_fast[dev_type])>>BFQ_RATE_SHIFT :
+				(1000000*R_slow[dev_type])>>BFQ_RATE_SHIFT,
+				(1000000*device_speed_thresh[dev_type])>>
+				BFQ_RATE_SHIFT);
 		}
+		/*
+		 * Caveat: processes doing IO in the slower disk zones
+		 * tend to be slow(er) even if not seeky. In this
+		 * respect, the estimated peak rate is likely to be an
+		 * average over the disk surface. Accordingly, to not
+		 * be too harsh with unlucky processes, a process is
+		 * deemed slow only if its bw has been lower than half
+		 * of the estimated peak rate.
+		 */
+		slow = bw < bfqd->peak_rate / 2;
 	}
 
-	/*
-	 * If the process has been served for a too short time
-	 * interval to let its possible sequential accesses prevail on
-	 * the initial seek time needed to move the disk head on the
-	 * first sector it requested, then give the process a chance
-	 * and for the moment return false.
-	 */
-	if (bfqq->entity.budget <= bfq_max_budget(bfqd) / 8)
-		return false;
+	bfq_log_bfqq(bfqd, bfqq,
+		     "update_peak_rate: bw %llu sect/s, peak rate %llu, "
+		     "slow %d",
+		     (1000000*bw)>>BFQ_RATE_SHIFT,
+		     (1000000*bfqd->peak_rate)>>BFQ_RATE_SHIFT,
+		     bw < bfqd->peak_rate / 2);
 
-	/*
-	 * A process is considered ``slow'' (i.e., seeky, so that we
-	 * cannot treat it fairly in the service domain, as it would
-	 * slow down too much the other processes) if, when a slice
-	 * ends for whatever reason, it has received service at a
-	 * rate that would not be high enough to complete the budget
-	 * before the budget timeout expiration.
-	 */
-	expected = bw * 1000 * timeout >> BFQ_RATE_SHIFT;
-
-	/*
-	 * Caveat: processes doing IO in the slower disk zones will
-	 * tend to be slow(er) even if not seeky. And the estimated
-	 * peak rate will actually be an average over the disk
-	 * surface. Hence, to not be too harsh with unlucky processes,
-	 * we keep a budget/3 margin of safety before declaring a
-	 * process slow.
-	 */
-	return expected > (4 * bfqq->entity.budget) / 3;
+	return slow;
 }
 
 /*
@@ -2191,6 +2705,15 @@ static bool bfq_update_peak_rate(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 static unsigned long bfq_bfqq_softrt_next_start(struct bfq_data *bfqd,
 						struct bfq_queue *bfqq)
 {
+	bfq_log_bfqq(bfqd, bfqq,
+		     "softrt_next_start: service_blkg %lu "
+		     "soft_rate %u sects/sec"
+		     "interval %u",
+		     bfqq->service_from_backlogged,
+		     bfqd->bfq_wr_max_softrt_rate,
+		     jiffies_to_msecs(HZ * bfqq->service_from_backlogged /
+				      bfqd->bfq_wr_max_softrt_rate));
+
 	return max(bfqq->last_idle_bklogged +
 		   HZ * bfqq->service_from_backlogged /
 		   bfqd->bfq_wr_max_softrt_rate,
@@ -2198,13 +2721,21 @@ static unsigned long bfq_bfqq_softrt_next_start(struct bfq_data *bfqd,
 }
 
 /*
- * Return the largest-possible time instant such that, for as long as possible,
- * the current time will be lower than this time instant according to the macro
- * time_is_before_jiffies().
+ * Return the farthest future time instant according to jiffies
+ * macros.
  */
-static unsigned long bfq_infinity_from_now(unsigned long now)
+static unsigned long bfq_greatest_from_now(void)
 {
-	return now + ULONG_MAX / 2;
+	return jiffies + MAX_JIFFY_OFFSET;
+}
+
+/*
+ * Return the farthest past time instant according to jiffies
+ * macros.
+ */
+static unsigned long bfq_smallest_from_now(void)
+{
+	return jiffies - MAX_JIFFY_OFFSET;
 }
 
 /**
@@ -2214,28 +2745,24 @@ static unsigned long bfq_infinity_from_now(unsigned long now)
  * @compensate: if true, compensate for the time spent idling.
  * @reason: the reason causing the expiration.
  *
+ * If the process associated with bfqq does slow I/O (e.g., because it
+ * issues random requests), we charge bfqq with the time it has been
+ * in service instead of the service it has received (see
+ * bfq_bfqq_charge_time for details on how this goal is achieved). As
+ * a consequence, bfqq will typically get higher timestamps upon
+ * reactivation, and hence it will be rescheduled as if it had
+ * received more service than what it has actually received. In the
+ * end, bfqq receives less service in proportion to how slowly its
+ * associated process consumes its budgets (and hence how seriously it
+ * tends to lower the throughput). In addition, this time-charging
+ * strategy guarantees time fairness among slow processes. In
+ * contrast, if the process associated with bfqq is not slow, we
+ * charge bfqq exactly with the service it has received.
  *
- * If the process associated to the queue is slow (i.e., seeky), or in
- * case of budget timeout, or, finally, if it is async, we
- * artificially charge it an entire budget (independently of the
- * actual service it received). As a consequence, the queue will get
- * higher timestamps than the correct ones upon reactivation, and
- * hence it will be rescheduled as if it had received more service
- * than what it actually received. In the end, this class of processes
- * will receive less service in proportion to how slowly they consume
- * their budgets (and hence how seriously they tend to lower the
- * throughput).
- *
- * In contrast, when a queue expires because it has been idling for
- * too much or because it exhausted its budget, we do not touch the
- * amount of service it has received. Hence when the queue will be
- * reactivated and its timestamps updated, the latter will be in sync
- * with the actual service received by the queue until expiration.
- *
- * Charging a full budget to the first type of queues and the exact
- * service to the others has the effect of using the WF2Q+ policy to
- * schedule the former on a timeslice basis, without violating the
- * service domain guarantees of the latter.
+ * Charging time to the first type of queues and the exact service to
+ * the other has the effect of using the WF2Q+ policy to schedule the
+ * former on a timeslice basis, without violating service domain
+ * guarantees among the latter.
  */
 static void bfq_bfqq_expire(struct bfq_data *bfqd,
 			    struct bfq_queue *bfqq,
@@ -2243,40 +2770,53 @@ static void bfq_bfqq_expire(struct bfq_data *bfqd,
 			    enum bfqq_expiration reason)
 {
 	bool slow;
+	unsigned long delta = 0;
+	struct bfq_entity *entity = &bfqq->entity;
+
 	BUG_ON(bfqq != bfqd->in_service_queue);
 
 	/*
-	 * Update disk peak rate for autotuning and check whether the
+	 * Update device peak rate for autotuning and check whether the
 	 * process is slow (see bfq_update_peak_rate).
 	 */
-	slow = bfq_update_peak_rate(bfqd, bfqq, compensate, reason);
+	slow = bfq_update_peak_rate(bfqd, bfqq, compensate, reason, &delta);
 
 	/*
-	 * As above explained, 'punish' slow (i.e., seeky), timed-out
-	 * and async queues, to favor sequential sync workloads.
+	 * Increase service_from_backlogged before next statement,
+	 * because the possible next invocation of
+	 * bfq_bfqq_charge_time would likely inflate
+	 * entity->service. In contrast, service_from_backlogged must
+	 * contain real service, to enable the soft real-time
+	 * heuristic to correctly compute the bandwidth consumed by
+	 * bfqq.
+	 */
+	bfqq->service_from_backlogged += entity->service;
+
+	/*
+	 * As above explained, charge slow (typically seeky) and
+	 * timed-out queues with the time and not the service
+	 * received, to favor sequential workloads.
 	 *
-	 * Processes doing I/O in the slower disk zones will tend to be
-	 * slow(er) even if not seeky. Hence, since the estimated peak
-	 * rate is actually an average over the disk surface, these
-	 * processes may timeout just for bad luck. To avoid punishing
-	 * them we do not charge a full budget to a process that
-	 * succeeded in consuming at least 2/3 of its budget.
+	 * Processes doing I/O in the slower disk zones will tend to
+	 * be slow(er) even if not seeky. Therefore, since the
+	 * estimated peak rate is actually an average over the disk
+	 * surface, these processes may timeout just for bad luck. To
+	 * avoid punishing them, do not charge time to processes that
+	 * succeeded in consuming at least 2/3 of their budget. This
+	 * allows BFQ to preserve enough elasticity to still perform
+	 * bandwidth, and not time, distribution with little unlucky
+	 * or quasi-sequential processes.
 	 */
-	if (slow || (reason == BFQ_BFQQ_BUDGET_TIMEOUT &&
-		     bfq_bfqq_budget_left(bfqq) >=  bfqq->entity.budget / 3))
-		bfq_bfqq_charge_full_budget(bfqq);
+	if (bfqq->wr_coeff == 1 &&
+	    (slow ||
+	     (reason == BFQ_BFQQ_BUDGET_TIMEOUT &&
+	      bfq_bfqq_budget_left(bfqq) >=  entity->budget / 3)))
+		bfq_bfqq_charge_time(bfqd, bfqq, delta);
 
-	bfqq->service_from_backlogged += bfqq->entity.service;
-
-	if (BFQQ_SEEKY(bfqq) && reason == BFQ_BFQQ_BUDGET_TIMEOUT &&
-	    !bfq_bfqq_constantly_seeky(bfqq)) {
-		bfq_mark_bfqq_constantly_seeky(bfqq);
-		if (!blk_queue_nonrot(bfqd->queue))
-			bfqd->const_seeky_busy_in_flight_queues++;
-	}
+	BUG_ON(bfqq->entity.budget < bfqq->entity.service);
 
 	if (reason == BFQ_BFQQ_TOO_IDLE &&
-	    bfqq->entity.service <= 2 * bfqq->entity.budget / 10 )
+	    entity->service <= 2 * entity->budget / 10 )
 		bfq_clear_bfqq_IO_bound(bfqq);
 
 	if (bfqd->low_latency && bfqq->wr_coeff == 1)
@@ -2285,19 +2825,23 @@ static void bfq_bfqq_expire(struct bfq_data *bfqd,
 	if (bfqd->low_latency && bfqd->bfq_wr_max_softrt_rate > 0 &&
 	    RB_EMPTY_ROOT(&bfqq->sort_list)) {
 		/*
-		 * If we get here, and there are no outstanding requests,
-		 * then the request pattern is isochronous (see the comments
-		 * to the function bfq_bfqq_softrt_next_start()). Hence we
-		 * can compute soft_rt_next_start. If, instead, the queue
-		 * still has outstanding requests, then we have to wait
-		 * for the completion of all the outstanding requests to
+		 * If we get here, and there are no outstanding
+		 * requests, then the request pattern is isochronous
+		 * (see the comments on the function
+		 * bfq_bfqq_softrt_next_start()). Thus we can compute
+		 * soft_rt_next_start. If, instead, the queue still
+		 * has outstanding requests, then we have to wait for
+		 * the completion of all the outstanding requests to
 		 * discover whether the request pattern is actually
 		 * isochronous.
 		 */
-		if (bfqq->dispatched == 0)
+		BUG_ON(bfqd->busy_queues < 1);
+		if (bfqq->dispatched == 0) {
 			bfqq->soft_rt_next_start =
 				bfq_bfqq_softrt_next_start(bfqd, bfqq);
-		else {
+			bfq_log_bfqq(bfqd, bfqq, "new soft_rt_next %lu",
+				     bfqq->soft_rt_next_start);
+		} else {
 			/*
 			 * The application is still waiting for the
 			 * completion of one or more requests:
@@ -2314,7 +2858,7 @@ static void bfq_bfqq_expire(struct bfq_data *bfqd,
 			 *    happened to be in the past.
 			 */
 			bfqq->soft_rt_next_start =
-				bfq_infinity_from_now(jiffies);
+				bfq_greatest_from_now();
 			/*
 			 * Schedule an update of soft_rt_next_start to when
 			 * the task may be discovered to be isochronous.
@@ -2324,15 +2868,27 @@ static void bfq_bfqq_expire(struct bfq_data *bfqd,
 	}
 
 	bfq_log_bfqq(bfqd, bfqq,
-		"expire (%d, slow %d, num_disp %d, idle_win %d)", reason,
-		slow, bfqq->dispatched, bfq_bfqq_idle_window(bfqq));
+		"expire (%d, slow %d, num_disp %d, idle_win %d, weight %d)",
+		     reason, slow, bfqq->dispatched,
+		     bfq_bfqq_idle_window(bfqq), entity->weight);
 
 	/*
 	 * Increase, decrease or leave budget unchanged according to
 	 * reason.
 	 */
+	BUG_ON(bfqq->entity.budget < bfqq->entity.service);
 	__bfq_bfqq_recalc_budget(bfqd, bfqq, reason);
+	BUG_ON(bfqq->next_rq == NULL &&
+	       bfqq->entity.budget < bfqq->entity.service);
 	__bfq_bfqq_expire(bfqd, bfqq);
+
+	BUG_ON(!bfq_bfqq_busy(bfqq) && reason == BFQ_BFQQ_BUDGET_EXHAUSTED &&
+		!bfq_class_idle(bfqq));
+
+	if (!bfq_bfqq_busy(bfqq) &&
+	    reason != BFQ_BFQQ_BUDGET_TIMEOUT &&
+	    reason != BFQ_BFQQ_BUDGET_EXHAUSTED)
+		bfq_mark_bfqq_non_blocking_wait_rq(bfqq);
 }
 
 /*
@@ -2342,20 +2898,17 @@ static void bfq_bfqq_expire(struct bfq_data *bfqd,
  */
 static bool bfq_bfqq_budget_timeout(struct bfq_queue *bfqq)
 {
-	if (bfq_bfqq_budget_new(bfqq) ||
-	    time_before(jiffies, bfqq->budget_timeout))
-		return false;
-	return true;
+	return time_is_before_eq_jiffies(bfqq->budget_timeout);
 }
 
 /*
- * If we expire a queue that is waiting for the arrival of a new
- * request, we may prevent the fictitious timestamp back-shifting that
- * allows the guarantees of the queue to be preserved (see [1] for
- * this tricky aspect). Hence we return true only if this condition
- * does not hold, or if the queue is slow enough to deserve only to be
- * kicked off for preserving a high throughput.
-*/
+ * If we expire a queue that is actively waiting (i.e., with the
+ * device idled) for the arrival of a new request, then we may incur
+ * the timestamp misalignment problem described in the body of the
+ * function __bfq_activate_entity. Hence we return true only if this
+ * condition does not hold, or if the queue is slow enough to deserve
+ * only to be kicked off for preserving a high throughput.
+ */
 static bool bfq_may_expire_for_budg_timeout(struct bfq_queue *bfqq)
 {
 	bfq_log_bfqq(bfqq->bfqd, bfqq,
@@ -2397,10 +2950,12 @@ static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
 {
 	struct bfq_data *bfqd = bfqq->bfqd;
 	bool idling_boosts_thr, idling_boosts_thr_without_issues,
-		all_queues_seeky, on_hdd_and_not_all_queues_seeky,
 		idling_needed_for_service_guarantees,
 		asymmetric_scenario;
 
+	if (bfqd->strict_guarantees)
+		return true;
+
 	/*
 	 * The next variable takes into account the cases where idling
 	 * boosts the throughput.
@@ -2422,7 +2977,7 @@ static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
 	 */
 	idling_boosts_thr = !bfqd->hw_tag ||
 		(!blk_queue_nonrot(bfqd->queue) && bfq_bfqq_IO_bound(bfqq) &&
-		 bfq_bfqq_idle_window(bfqq)) ;
+		 bfq_bfqq_idle_window(bfqq));
 
 	/*
 	 * The value of the next variable,
@@ -2463,74 +3018,27 @@ static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
 		bfqd->wr_busy_queues == 0;
 
 	/*
-	 * There are then two cases where idling must be performed not
+	 * There is then a case where idling must be performed not
 	 * for throughput concerns, but to preserve service
-	 * guarantees. In the description of these cases, we say, for
-	 * short, that a queue is sequential/random if the process
-	 * associated to the queue issues sequential/random requests
-	 * (in the second case the queue may be tagged as seeky or
-	 * even constantly_seeky).
+	 * guarantees.
 	 *
-	 * To introduce the first case, we note that, since
-	 * bfq_bfqq_idle_window(bfqq) is false if the device is
-	 * NCQ-capable and bfqq is random (see
-	 * bfq_update_idle_window()), then, from the above two
-	 * assignments it follows that
-	 * idling_boosts_thr_without_issues is false if the device is
-	 * NCQ-capable and bfqq is random. Therefore, for this case,
-	 * device idling would never be allowed if we used just
-	 * idling_boosts_thr_without_issues to decide whether to allow
-	 * it. And, beneficially, this would imply that throughput
-	 * would always be boosted also with random I/O on NCQ-capable
-	 * HDDs.
-	 *
-	 * But we must be careful on this point, to avoid an unfair
-	 * treatment for bfqq. In fact, because of the same above
-	 * assignments, idling_boosts_thr_without_issues is, on the
-	 * other hand, true if 1) the device is an HDD and bfqq is
-	 * sequential, and 2) there are no busy weight-raised
-	 * queues. As a consequence, if we used just
-	 * idling_boosts_thr_without_issues to decide whether to idle
-	 * the device, then with an HDD we might easily bump into a
-	 * scenario where queues that are sequential and I/O-bound
-	 * would enjoy idling, whereas random queues would not. The
-	 * latter might then get a low share of the device throughput,
-	 * simply because the former would get many requests served
-	 * after being set as in service, while the latter would not.
-	 *
-	 * To address this issue, we start by setting to true a
-	 * sentinel variable, on_hdd_and_not_all_queues_seeky, if the
-	 * device is rotational and not all queues with pending or
-	 * in-flight requests are constantly seeky (i.e., there are
-	 * active sequential queues, and bfqq might then be mistreated
-	 * if it does not enjoy idling because it is random).
-	 */
-	all_queues_seeky = bfq_bfqq_constantly_seeky(bfqq) &&
-			   bfqd->busy_in_flight_queues ==
-			   bfqd->const_seeky_busy_in_flight_queues;
-
-	on_hdd_and_not_all_queues_seeky =
-		!blk_queue_nonrot(bfqd->queue) && !all_queues_seeky;
-
-	/*
-	 * To introduce the second case where idling needs to be
-	 * performed to preserve service guarantees, we can note that
-	 * allowing the drive to enqueue more than one request at a
-	 * time, and hence delegating de facto final scheduling
-	 * decisions to the drive's internal scheduler, causes loss of
-	 * control on the actual request service order. In particular,
-	 * the critical situation is when requests from different
-	 * processes happens to be present, at the same time, in the
-	 * internal queue(s) of the drive. In such a situation, the
-	 * drive, by deciding the service order of the
-	 * internally-queued requests, does determine also the actual
-	 * throughput distribution among these processes. But the
-	 * drive typically has no notion or concern about per-process
-	 * throughput distribution, and makes its decisions only on a
-	 * per-request basis. Therefore, the service distribution
-	 * enforced by the drive's internal scheduler is likely to
-	 * coincide with the desired device-throughput distribution
-	 * only in a completely symmetric scenario where:
+	 * To introduce this case, we can note that allowing the drive
+	 * to enqueue more than one request at a time, and hence
+	 * delegating de facto final scheduling decisions to the
+	 * drive's internal scheduler, entails loss of control on the
+	 * actual request service order. In particular, the critical
+	 * situation is when requests from different processes happen
+	 * to be present, at the same time, in the internal queue(s)
+	 * of the drive. In such a situation, the drive, by deciding
+	 * the service order of the internally-queued requests, does
+	 * determine also the actual throughput distribution among
+	 * these processes. But the drive typically has no notion or
+	 * concern about per-process throughput distribution, and
+	 * makes its decisions only on a per-request basis. Therefore,
+	 * the service distribution enforced by the drive's internal
+	 * scheduler is likely to coincide with the desired
+	 * device-throughput distribution only in a completely
+	 * symmetric scenario where:
 	 * (i)  each of these processes must get the same throughput as
 	 *      the others;
 	 * (ii) all these processes have the same I/O pattern
@@ -2552,26 +3060,53 @@ static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
 	 * words, only if sub-condition (i) holds, then idling is
 	 * allowed, and the device tends to be prevented from queueing
 	 * many requests, possibly of several processes. The reason
-	 * for not controlling also sub-condition (ii) is that, first,
-	 * in the case of an HDD, the asymmetry in terms of types of
-	 * I/O patterns is already taken in to account in the above
-	 * sentinel variable
-	 * on_hdd_and_not_all_queues_seeky. Secondly, in the case of a
-	 * flash-based device, we prefer however to privilege
-	 * throughput (and idling lowers throughput for this type of
-	 * devices), for the following reasons:
-	 * 1) differently from HDDs, the service time of random
-	 *    requests is not orders of magnitudes lower than the service
-	 *    time of sequential requests; thus, even if processes doing
-	 *    sequential I/O get a preferential treatment with respect to
-	 *    others doing random I/O, the consequences are not as
-	 *    dramatic as with HDDs;
-	 * 2) if a process doing random I/O does need strong
-	 *    throughput guarantees, it is hopefully already being
-	 *    weight-raised, or the user is likely to have assigned it a
-	 *    higher weight than the other processes (and thus
-	 *    sub-condition (i) is likely to be false, which triggers
-	 *    idling).
+	 * for not controlling also sub-condition (ii) is that we
+	 * exploit preemption to preserve guarantees in case of
+	 * symmetric scenarios, even if (ii) does not hold, as
+	 * explained in the next two paragraphs.
+	 *
+	 * Even if a queue, say Q, is expired when it remains idle, Q
+	 * can still preempt the new in-service queue if the next
+	 * request of Q arrives soon (see the comments on
+	 * bfq_bfqq_update_budg_for_activation). If all queues and
+	 * groups have the same weight, this form of preemption,
+	 * combined with the hole-recovery heuristic described in the
+	 * comments on function bfq_bfqq_update_budg_for_activation,
+	 * are enough to preserve a correct bandwidth distribution in
+	 * the mid term, even without idling. In fact, even if not
+	 * idling allows the internal queues of the device to contain
+	 * many requests, and thus to reorder requests, we can rather
+	 * safely assume that the internal scheduler still preserves a
+	 * minimum of mid-term fairness. The motivation for using
+	 * preemption instead of idling is that, by not idling,
+	 * service guarantees are preserved without minimally
+	 * sacrificing throughput. In other words, both a high
+	 * throughput and its desired distribution are obtained.
+	 *
+	 * More precisely, this preemption-based, idleless approach
+	 * provides fairness in terms of IOPS, and not sectors per
+	 * second. This can be seen with a simple example. Suppose
+	 * that there are two queues with the same weight, but that
+	 * the first queue receives requests of 8 sectors, while the
+	 * second queue receives requests of 1024 sectors. In
+	 * addition, suppose that each of the two queues contains at
+	 * most one request at a time, which implies that each queue
+	 * always remains idle after it is served. Finally, after
+	 * remaining idle, each queue receives very quickly a new
+	 * request. It follows that the two queues are served
+	 * alternatively, preempting each other if needed. This
+	 * implies that, although both queues have the same weight,
+	 * the queue with large requests receives a service that is
+	 * 1024/8 times as high as the service received by the other
+	 * queue.
+	 *
+	 * On the other hand, device idling is performed, and thus
+	 * pure sector-domain guarantees are provided, for the
+	 * following queues, which are likely to need stronger
+	 * throughput guarantees: weight-raised queues, and queues
+	 * with a higher weight than other queues. When such queues
+	 * are active, sub-condition (i) is false, which triggers
+	 * device idling.
 	 *
 	 * According to the above considerations, the next variable is
 	 * true (only) if sub-condition (i) holds. To compute the
@@ -2579,7 +3114,7 @@ static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
 	 * the function bfq_symmetric_scenario(), but also check
 	 * whether bfqq is being weight-raised, because
 	 * bfq_symmetric_scenario() does not take into account also
-	 * weight-raised queues (see comments to
+	 * weight-raised queues (see comments on
 	 * bfq_weights_tree_add()).
 	 *
 	 * As a side note, it is worth considering that the above
@@ -2601,17 +3136,16 @@ static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
 	 * bfqq. Such a case is when bfqq became active in a burst of
 	 * queue activations. Queues that became active during a large
 	 * burst benefit only from throughput, as discussed in the
-	 * comments to bfq_handle_burst. Thus, if bfqq became active
+	 * comments on bfq_handle_burst. Thus, if bfqq became active
 	 * in a burst and not idling the device maximizes throughput,
 	 * then the device must no be idled, because not idling the
 	 * device provides bfqq and all other queues in the burst with
-	 * maximum benefit. Combining this and the two cases above, we
-	 * can now establish when idling is actually needed to
-	 * preserve service guarantees.
+	 * maximum benefit. Combining this and the above case, we can
+	 * now establish when idling is actually needed to preserve
+	 * service guarantees.
 	 */
 	idling_needed_for_service_guarantees =
-		(on_hdd_and_not_all_queues_seeky || asymmetric_scenario) &&
-		!bfq_bfqq_in_large_burst(bfqq);
+		asymmetric_scenario && !bfq_bfqq_in_large_burst(bfqq);
 
 	/*
 	 * We have now all the components we need to compute the return
@@ -2621,6 +3155,14 @@ static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
 	 * 2) idling either boosts the throughput (without issues), or
 	 *    is necessary to preserve service guarantees.
 	 */
+	bfq_log_bfqq(bfqd, bfqq, "may_idle: sync %d idling_boosts_thr %d "
+		     "wr_busy %d boosts %d IO-bound %d guar %d",
+		     bfq_bfqq_sync(bfqq), idling_boosts_thr,
+		     bfqd->wr_busy_queues,
+		     idling_boosts_thr_without_issues,
+		     bfq_bfqq_IO_bound(bfqq),
+		     idling_needed_for_service_guarantees);
+
 	return bfq_bfqq_sync(bfqq) &&
 		(idling_boosts_thr_without_issues ||
 		 idling_needed_for_service_guarantees);
@@ -2632,7 +3174,7 @@ static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
  * 1) the queue must remain in service and cannot be expired, and
  * 2) the device must be idled to wait for the possible arrival of a new
  *    request for the queue.
- * See the comments to the function bfq_bfqq_may_idle for the reasons
+ * See the comments on the function bfq_bfqq_may_idle for the reasons
  * why performing device idling is the best choice to boost the throughput
  * and preserve service guarantees when bfq_bfqq_may_idle itself
  * returns true.
@@ -2698,9 +3240,7 @@ static struct bfq_queue *bfq_select_queue(struct bfq_data *bfqd)
 				 */
 				bfq_clear_bfqq_wait_request(bfqq);
 				del_timer(&bfqd->idle_slice_timer);
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
 				bfqg_stats_update_idle_time(bfqq_group(bfqq));
-#endif
 			}
 			goto keep_queue;
 		}
@@ -2745,14 +3285,11 @@ static void bfq_update_wr_data(struct bfq_data *bfqd, struct bfq_queue *bfqq)
 			bfq_log_bfqq(bfqd, bfqq, "WARN: pending prio change");
 
 		/*
-		 * If the queue was activated in a burst, or
-		 * too much time has elapsed from the beginning
-		 * of this weight-raising period, or the queue has
-		 * exceeded the acceptable number of cooperations,
-		 * then end weight raising.
+		 * If the queue was activated in a burst, or too much
+		 * time has elapsed from the beginning of this
+		 * weight-raising period, then end weight raising.
 		 */
 		if (bfq_bfqq_in_large_burst(bfqq) ||
-		    bfq_bfqq_cooperations(bfqq) >= bfqd->bfq_coop_thresh ||
 		    time_is_before_jiffies(bfqq->last_wr_start_finish +
 					   bfqq->wr_cur_max_time)) {
 			bfqq->last_wr_start_finish = jiffies;
@@ -2811,13 +3348,29 @@ static int bfq_dispatch_request(struct bfq_data *bfqd,
 		 */
 		if (!bfqd->rq_in_driver)
 			bfq_schedule_dispatch(bfqd);
+		BUG_ON(bfqq->entity.budget < bfqq->entity.service);
 		goto expire;
 	}
 
+	BUG_ON(bfqq->entity.budget < bfqq->entity.service);
 	/* Finally, insert request into driver dispatch list. */
 	bfq_bfqq_served(bfqq, service_to_charge);
+
+	BUG_ON(bfqq->entity.budget < bfqq->entity.service);
+
 	bfq_dispatch_insert(bfqd->queue, rq);
 
+	/*
+	 * If weight raising has to terminate for bfqq, then next
+	 * function causes an immediate update of bfqq's weight,
+	 * without waiting for next activation. As a consequence, on
+	 * expiration, bfqq will be timestamped as if has never been
+	 * weight-raised during this service slot, even if it has
+	 * received part or even most of the service as a
+	 * weight-raised queue. This inflates bfqq's timestamps, which
+	 * is beneficial, as bfqq is then more willing to leave the
+	 * device immediately to possible other weight-raised queues.
+	 */
 	bfq_update_wr_data(bfqd, bfqq);
 
 	bfq_log_bfqq(bfqd, bfqq,
@@ -2833,9 +3386,7 @@ static int bfq_dispatch_request(struct bfq_data *bfqd,
 		bfqd->in_service_bic = RQ_BIC(rq);
 	}
 
-	if (bfqd->busy_queues > 1 && ((!bfq_bfqq_sync(bfqq) &&
-	    dispatched >= bfqd->bfq_max_budget_async_rq) ||
-	    bfq_class_idle(bfqq)))
+	if (bfqd->busy_queues > 1 && bfq_class_idle(bfqq))
 		goto expire;
 
 	return dispatched;
@@ -2881,8 +3432,8 @@ static int bfq_forced_dispatch(struct bfq_data *bfqd)
 		st = bfq_entity_service_tree(&bfqq->entity);
 
 		dispatched += __bfq_forced_dispatch_bfqq(bfqq);
+
 		bfqq->max_budget = bfq_max_budget(bfqd);
-
 		bfq_forget_idle(st);
 	}
 
@@ -2895,9 +3446,9 @@ static int bfq_dispatch_requests(struct request_queue *q, int force)
 {
 	struct bfq_data *bfqd = q->elevator->elevator_data;
 	struct bfq_queue *bfqq;
-	int max_dispatch;
 
 	bfq_log(bfqd, "dispatch requests: %d busy queues", bfqd->busy_queues);
+
 	if (bfqd->busy_queues == 0)
 		return 0;
 
@@ -2908,21 +3459,7 @@ static int bfq_dispatch_requests(struct request_queue *q, int force)
 	if (!bfqq)
 		return 0;
 
-	if (bfq_class_idle(bfqq))
-		max_dispatch = 1;
-
-	if (!bfq_bfqq_sync(bfqq))
-		max_dispatch = bfqd->bfq_max_budget_async_rq;
-
-	if (!bfq_bfqq_sync(bfqq) && bfqq->dispatched >= max_dispatch) {
-		if (bfqd->busy_queues > 1)
-			return 0;
-		if (bfqq->dispatched >= 4 * max_dispatch)
-			return 0;
-	}
-
-	if (bfqd->sync_flight != 0 && !bfq_bfqq_sync(bfqq))
-		return 0;
+	BUG_ON(bfqq->entity.budget < bfqq->entity.service);
 
 	bfq_clear_bfqq_wait_request(bfqq);
 	BUG_ON(timer_pending(&bfqd->idle_slice_timer));
@@ -2933,6 +3470,8 @@ static int bfq_dispatch_requests(struct request_queue *q, int force)
 	bfq_log_bfqq(bfqd, bfqq, "dispatched %s request",
 			bfq_bfqq_sync(bfqq) ? "sync" : "async");
 
+	BUG_ON(bfqq->next_rq == NULL &&
+	       bfqq->entity.budget < bfqq->entity.service);
 	return 1;
 }
 
@@ -2944,23 +3483,22 @@ static int bfq_dispatch_requests(struct request_queue *q, int force)
  */
 static void bfq_put_queue(struct bfq_queue *bfqq)
 {
-	struct bfq_data *bfqd = bfqq->bfqd;
 #ifdef CONFIG_BFQ_GROUP_IOSCHED
 	struct bfq_group *bfqg = bfqq_group(bfqq);
 #endif
 
-	BUG_ON(atomic_read(&bfqq->ref) <= 0);
+	BUG_ON(bfqq->ref <= 0);
 
-	bfq_log_bfqq(bfqd, bfqq, "put_queue: %p %d", bfqq,
-		     atomic_read(&bfqq->ref));
-	if (!atomic_dec_and_test(&bfqq->ref))
+	bfq_log_bfqq(bfqq->bfqd, bfqq, "put_queue: %p %d", bfqq, bfqq->ref);
+	bfqq->ref--;
+	if (bfqq->ref)
 		return;
 
 	BUG_ON(rb_first(&bfqq->sort_list));
 	BUG_ON(bfqq->allocated[READ] + bfqq->allocated[WRITE] != 0);
 	BUG_ON(bfqq->entity.tree);
 	BUG_ON(bfq_bfqq_busy(bfqq));
-	BUG_ON(bfqd->in_service_queue == bfqq);
+	BUG_ON(bfqq->bfqd->in_service_queue == bfqq);
 
 	if (bfq_bfqq_sync(bfqq))
 		/*
@@ -2973,7 +3511,7 @@ static void bfq_put_queue(struct bfq_queue *bfqq)
 		 */
 		hlist_del_init(&bfqq->burst_list_node);
 
-	bfq_log_bfqq(bfqd, bfqq, "put_queue: %p freed", bfqq);
+	bfq_log_bfqq(bfqq->bfqd, bfqq, "put_queue: %p freed", bfqq);
 
 	kmem_cache_free(bfq_pool, bfqq);
 #ifdef CONFIG_BFQ_GROUP_IOSCHED
@@ -3007,8 +3545,7 @@ static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
 		bfq_schedule_dispatch(bfqd);
 	}
 
-	bfq_log_bfqq(bfqd, bfqq, "exit_bfqq: %p, %d", bfqq,
-		     atomic_read(&bfqq->ref));
+	bfq_log_bfqq(bfqd, bfqq, "exit_bfqq: %p, %d", bfqq, bfqq->ref);
 
 	bfq_put_cooperator(bfqq);
 
@@ -3019,26 +3556,7 @@ static void bfq_init_icq(struct io_cq *icq)
 {
 	struct bfq_io_cq *bic = icq_to_bic(icq);
 
-	bic->ttime.last_end_request = jiffies;
-	/*
-	 * A newly created bic indicates that the process has just
-	 * started doing I/O, and is probably mapping into memory its
-	 * executable and libraries: it definitely needs weight raising.
-	 * There is however the possibility that the process performs,
-	 * for a while, I/O close to some other process. EQM intercepts
-	 * this behavior and may merge the queue corresponding to the
-	 * process  with some other queue, BEFORE the weight of the queue
-	 * is raised. Merged queues are not weight-raised (they are assumed
-	 * to belong to processes that benefit only from high throughput).
-	 * If the merge is basically the consequence of an accident, then
-	 * the queue will be split soon and will get back its old weight.
-	 * It is then important to write down somewhere that this queue
-	 * does need weight raising, even if it did not make it to get its
-	 * weight raised before being merged. To this purpose, we overload
-	 * the field raising_time_left and assign 1 to it, to mark the queue
-	 * as needing weight raising.
-	 */
-	bic->wr_time_left = 1;
+	bic->ttime.last_end_request = bfq_smallest_from_now();
 }
 
 static void bfq_exit_icq(struct io_cq *icq)
@@ -3046,21 +3564,21 @@ static void bfq_exit_icq(struct io_cq *icq)
 	struct bfq_io_cq *bic = icq_to_bic(icq);
 	struct bfq_data *bfqd = bic_to_bfqd(bic);
 
-	if (bic->bfqq[BLK_RW_ASYNC]) {
-		bfq_exit_bfqq(bfqd, bic->bfqq[BLK_RW_ASYNC]);
-		bic->bfqq[BLK_RW_ASYNC] = NULL;
+	if (bic_to_bfqq(bic, false)) {
+		bfq_exit_bfqq(bfqd, bic_to_bfqq(bic, false));
+		bic_set_bfqq(bic, NULL, false);
 	}
 
-	if (bic->bfqq[BLK_RW_SYNC]) {
+	if (bic_to_bfqq(bic, true)) {
 		/*
 		 * If the bic is using a shared queue, put the reference
 		 * taken on the io_context when the bic started using a
 		 * shared bfq_queue.
 		 */
-		if (bfq_bfqq_coop(bic->bfqq[BLK_RW_SYNC]))
+		if (bfq_bfqq_coop(bic_to_bfqq(bic, true)))
 			put_io_context(icq->ioc);
-		bfq_exit_bfqq(bfqd, bic->bfqq[BLK_RW_SYNC]);
-		bic->bfqq[BLK_RW_SYNC] = NULL;
+		bfq_exit_bfqq(bfqd, bic_to_bfqq(bic, true));
+		bic_set_bfqq(bic, NULL, true);
 	}
 }
 
@@ -3068,7 +3586,8 @@ static void bfq_exit_icq(struct io_cq *icq)
  * Update the entity prio values; note that the new values will not
  * be used until the next (re)activation.
  */
-static void bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *bic)
+static void bfq_set_next_ioprio_data(struct bfq_queue *bfqq,
+				     struct bfq_io_cq *bic)
 {
 	struct task_struct *tsk = current;
 	int ioprio_class;
@@ -3100,7 +3619,7 @@ static void bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *b
 		break;
 	}
 
-	if (bfqq->new_ioprio < 0 || bfqq->new_ioprio >= IOPRIO_BE_NR) {
+	if (bfqq->new_ioprio >= IOPRIO_BE_NR) {
 		printk(KERN_CRIT "bfq_set_next_ioprio_data: new_ioprio %d\n",
 				 bfqq->new_ioprio);
 		BUG();
@@ -3108,45 +3627,40 @@ static void bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *b
 
 	bfqq->entity.new_weight = bfq_ioprio_to_weight(bfqq->new_ioprio);
 	bfqq->entity.prio_changed = 1;
+	bfq_log_bfqq(bfqq->bfqd, bfqq,
+		     "set_next_ioprio_data: bic_class %d prio %d class %d",
+		     ioprio_class, bfqq->new_ioprio, bfqq->new_ioprio_class);
 }
 
 static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio)
 {
-	struct bfq_data *bfqd;
-	struct bfq_queue *bfqq, *new_bfqq;
+	struct bfq_data *bfqd = bic_to_bfqd(bic);
+	struct bfq_queue *bfqq;
 	unsigned long uninitialized_var(flags);
 	int ioprio = bic->icq.ioc->ioprio;
 
-	bfqd = bfq_get_bfqd_locked(&(bic->icq.q->elevator->elevator_data),
-				   &flags);
 	/*
 	 * This condition may trigger on a newly created bic, be sure to
 	 * drop the lock before returning.
 	 */
 	if (unlikely(!bfqd) || likely(bic->ioprio == ioprio))
-		goto out;
+		return;
 
 	bic->ioprio = ioprio;
 
-	bfqq = bic->bfqq[BLK_RW_ASYNC];
+	bfqq = bic_to_bfqq(bic, false);
 	if (bfqq) {
-		new_bfqq = bfq_get_queue(bfqd, bio, BLK_RW_ASYNC, bic,
-					 GFP_ATOMIC);
-		if (new_bfqq) {
-			bic->bfqq[BLK_RW_ASYNC] = new_bfqq;
-			bfq_log_bfqq(bfqd, bfqq,
-				     "check_ioprio_change: bfqq %p %d",
-				     bfqq, atomic_read(&bfqq->ref));
-			bfq_put_queue(bfqq);
-		}
+		bfq_put_queue(bfqq);
+		bfqq = bfq_get_queue(bfqd, bio, BLK_RW_ASYNC, bic);
+		bic_set_bfqq(bic, bfqq, false);
+		bfq_log_bfqq(bfqd, bfqq,
+			     "check_ioprio_change: bfqq %p %d",
+			     bfqq, bfqq->ref);
 	}
 
-	bfqq = bic->bfqq[BLK_RW_SYNC];
+	bfqq = bic_to_bfqq(bic, true);
 	if (bfqq)
 		bfq_set_next_ioprio_data(bfqq, bic);
-
-out:
-	bfq_put_bfqd_unlock(bfqd, &flags);
 }
 
 static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
@@ -3155,8 +3669,9 @@ static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 	RB_CLEAR_NODE(&bfqq->entity.rb_node);
 	INIT_LIST_HEAD(&bfqq->fifo);
 	INIT_HLIST_NODE(&bfqq->burst_list_node);
+	BUG_ON(!hlist_unhashed(&bfqq->burst_list_node));
 
-	atomic_set(&bfqq->ref, 0);
+	bfqq->ref = 0;
 	bfqq->bfqd = bfqd;
 
 	if (bic)
@@ -3166,6 +3681,7 @@ static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 		if (!bfq_class_idle(bfqq))
 			bfq_mark_bfqq_idle_window(bfqq);
 		bfq_mark_bfqq_sync(bfqq);
+		bfq_mark_bfqq_just_created(bfqq);
 	} else
 		bfq_clear_bfqq_sync(bfqq);
 	bfq_mark_bfqq_IO_bound(bfqq);
@@ -3175,72 +3691,17 @@ static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 	bfqq->pid = pid;
 
 	bfqq->wr_coeff = 1;
-	bfqq->last_wr_start_finish = 0;
+	bfqq->last_wr_start_finish = bfq_smallest_from_now();
+	bfqq->budget_timeout = bfq_smallest_from_now();
+	bfqq->split_time = bfq_smallest_from_now();
 	/*
 	 * Set to the value for which bfqq will not be deemed as
 	 * soft rt when it becomes backlogged.
 	 */
-	bfqq->soft_rt_next_start = bfq_infinity_from_now(jiffies);
-}
+	bfqq->soft_rt_next_start = bfq_greatest_from_now();
 
-static struct bfq_queue *bfq_find_alloc_queue(struct bfq_data *bfqd,
-					      struct bio *bio, int is_sync,
-					      struct bfq_io_cq *bic,
-					      gfp_t gfp_mask)
-{
-	struct bfq_group *bfqg;
-	struct bfq_queue *bfqq, *new_bfqq = NULL;
-	struct blkcg *blkcg;
-
-retry:
-	rcu_read_lock();
-
-	blkcg = bio_blkcg(bio);
-	bfqg = bfq_find_alloc_group(bfqd, blkcg);
-	/* bic always exists here */
-	bfqq = bic_to_bfqq(bic, is_sync);
-
-	/*
-	 * Always try a new alloc if we fall back to the OOM bfqq
-	 * originally, since it should just be a temporary situation.
-	 */
-	if (!bfqq || bfqq == &bfqd->oom_bfqq) {
-		bfqq = NULL;
-		if (new_bfqq) {
-			bfqq = new_bfqq;
-			new_bfqq = NULL;
-		} else if (gfpflags_allow_blocking(gfp_mask)) {
-			rcu_read_unlock();
-			spin_unlock_irq(bfqd->queue->queue_lock);
-			new_bfqq = kmem_cache_alloc_node(bfq_pool,
-					gfp_mask | __GFP_ZERO,
-					bfqd->queue->node);
-			spin_lock_irq(bfqd->queue->queue_lock);
-			if (new_bfqq)
-				goto retry;
-		} else {
-			bfqq = kmem_cache_alloc_node(bfq_pool,
-					gfp_mask | __GFP_ZERO,
-					bfqd->queue->node);
-		}
-
-		if (bfqq) {
-			bfq_init_bfqq(bfqd, bfqq, bic, current->pid,
-                                      is_sync);
-			bfq_init_entity(&bfqq->entity, bfqg);
-			bfq_log_bfqq(bfqd, bfqq, "allocated");
-		} else {
-			bfqq = &bfqd->oom_bfqq;
-			bfq_log_bfqq(bfqd, bfqq, "using oom bfqq");
-		}
-	}
-
-	if (new_bfqq)
-		kmem_cache_free(bfq_pool, new_bfqq);
-
-	rcu_read_unlock();
-
-	return bfqq;
+	/* first request is almost certainly seeky */
+	bfqq->seek_history = 1;
 }
 
 static struct bfq_queue **bfq_async_queue_prio(struct bfq_data *bfqd,
@@ -3263,44 +3724,60 @@ static struct bfq_queue **bfq_async_queue_prio(struct bfq_data *bfqd,
 }
 
 static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
-				       struct bio *bio, int is_sync,
-				       struct bfq_io_cq *bic, gfp_t gfp_mask)
+				       struct bio *bio, bool is_sync,
+				       struct bfq_io_cq *bic)
 {
 	const int ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
 	const int ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
 	struct bfq_queue **async_bfqq = NULL;
-	struct bfq_queue *bfqq = NULL;
+	struct bfq_queue *bfqq;
+	struct bfq_group *bfqg;
+
+	rcu_read_lock();
+
+	bfqg = bfq_find_set_group(bfqd,bio_blkcg(bio));
+	if (!bfqg) {
+		bfqq = &bfqd->oom_bfqq;
+		goto out;
+	}
 
 	if (!is_sync) {
-		struct blkcg *blkcg;
-		struct bfq_group *bfqg;
-
-		rcu_read_lock();
-		blkcg = bio_blkcg(bio);
-		rcu_read_unlock();
-		bfqg = bfq_find_alloc_group(bfqd, blkcg);
 		async_bfqq = bfq_async_queue_prio(bfqd, bfqg, ioprio_class,
 						  ioprio);
 		bfqq = *async_bfqq;
+		if (bfqq)
+			goto out;
 	}
 
-	if (!bfqq)
-		bfqq = bfq_find_alloc_queue(bfqd, bio, is_sync, bic, gfp_mask);
+	bfqq = kmem_cache_alloc_node(bfq_pool, GFP_NOWAIT | __GFP_ZERO,
+				     bfqd->queue->node);
+
+	if (bfqq) {
+		bfq_init_bfqq(bfqd, bfqq, bic, current->pid,
+			      is_sync);
+		bfq_init_entity(&bfqq->entity, bfqg);
+		bfq_log_bfqq(bfqd, bfqq, "allocated");
+	} else {
+		bfqq = &bfqd->oom_bfqq;
+		bfq_log_bfqq(bfqd, bfqq, "using oom bfqq");
+		goto out;
+	}
 
 	/*
 	 * Pin the queue now that it's allocated, scheduler exit will
 	 * prune it.
 	 */
-	if (!is_sync && !(*async_bfqq)) {
-		atomic_inc(&bfqq->ref);
+	if (async_bfqq) {
+		bfqq->ref++;
 		bfq_log_bfqq(bfqd, bfqq, "get_queue, bfqq not in async: %p, %d",
-			     bfqq, atomic_read(&bfqq->ref));
+			     bfqq, bfqq->ref);
 		*async_bfqq = bfqq;
 	}
 
-	atomic_inc(&bfqq->ref);
-	bfq_log_bfqq(bfqd, bfqq, "get_queue, at end: %p, %d", bfqq,
-		     atomic_read(&bfqq->ref));
+out:
+	bfqq->ref++;
+	bfq_log_bfqq(bfqd, bfqq, "get_queue, at end: %p, %d", bfqq, bfqq->ref);
+	rcu_read_unlock();
 	return bfqq;
 }
 
@@ -3316,37 +3793,21 @@ static void bfq_update_io_thinktime(struct bfq_data *bfqd,
 				bic->ttime.ttime_samples;
 }
 
-static void bfq_update_io_seektime(struct bfq_data *bfqd,
-				   struct bfq_queue *bfqq,
-				   struct request *rq)
+
+static void
+bfq_update_io_seektime(struct bfq_data *bfqd, struct bfq_queue *bfqq,
+		       struct request *rq)
 {
-	sector_t sdist;
-	u64 total;
-
-	if (bfqq->last_request_pos < blk_rq_pos(rq))
-		sdist = blk_rq_pos(rq) - bfqq->last_request_pos;
-	else
-		sdist = bfqq->last_request_pos - blk_rq_pos(rq);
-
-	/*
-	 * Don't allow the seek distance to get too large from the
-	 * odd fragment, pagein, etc.
-	 */
-	if (bfqq->seek_samples == 0) /* first request, not really a seek */
-		sdist = 0;
-	else if (bfqq->seek_samples <= 60) /* second & third seek */
-		sdist = min(sdist, (bfqq->seek_mean * 4) + 2*1024*1024);
-	else
-		sdist = min(sdist, (bfqq->seek_mean * 4) + 2*1024*64);
-
-	bfqq->seek_samples = (7*bfqq->seek_samples + 256) / 8;
-	bfqq->seek_total = (7*bfqq->seek_total + (u64)256*sdist) / 8;
-	total = bfqq->seek_total + (bfqq->seek_samples/2);
-	do_div(total, bfqq->seek_samples);
-	bfqq->seek_mean = (sector_t)total;
-
-	bfq_log_bfqq(bfqd, bfqq, "dist=%llu mean=%llu", (u64)sdist,
-			(u64)bfqq->seek_mean);
+	sector_t sdist = 0;
+	if (bfqq->last_request_pos) {
+		if (bfqq->last_request_pos < blk_rq_pos(rq))
+			sdist = blk_rq_pos(rq) - bfqq->last_request_pos;
+		else
+			sdist = bfqq->last_request_pos - blk_rq_pos(rq);
+	}
+
+	bfqq->seek_history <<= 1;
+	bfqq->seek_history |= (sdist > BFQQ_SEEK_THR);
 }
 
 /*
@@ -3364,7 +3825,8 @@ static void bfq_update_idle_window(struct bfq_data *bfqd,
 		return;
 
 	/* Idle window just restored, statistics are meaningless. */
-	if (bfq_bfqq_just_split(bfqq))
+	if (time_is_after_eq_jiffies(bfqq->split_time +
+				     bfqd->bfq_wr_min_idle_time))
 		return;
 
 	enable_idle = bfq_bfqq_idle_window(bfqq);
@@ -3404,22 +3866,13 @@ static void bfq_rq_enqueued(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 
 	bfq_update_io_thinktime(bfqd, bic);
 	bfq_update_io_seektime(bfqd, bfqq, rq);
-	if (!BFQQ_SEEKY(bfqq) && bfq_bfqq_constantly_seeky(bfqq)) {
-		bfq_clear_bfqq_constantly_seeky(bfqq);
-		if (!blk_queue_nonrot(bfqd->queue)) {
-			BUG_ON(!bfqd->const_seeky_busy_in_flight_queues);
-			bfqd->const_seeky_busy_in_flight_queues--;
-		}
-	}
 	if (bfqq->entity.service > bfq_max_budget(bfqd) / 8 ||
 	    !BFQQ_SEEKY(bfqq))
 		bfq_update_idle_window(bfqd, bfqq, bic);
-	bfq_clear_bfqq_just_split(bfqq);
 
 	bfq_log_bfqq(bfqd, bfqq,
-		     "rq_enqueued: idle_window=%d (seeky %d, mean %llu)",
-		     bfq_bfqq_idle_window(bfqq), BFQQ_SEEKY(bfqq),
-		     (long long unsigned)bfqq->seek_mean);
+		     "rq_enqueued: idle_window=%d (seeky %d)",
+		     bfq_bfqq_idle_window(bfqq), BFQQ_SEEKY(bfqq));
 
 	bfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);
 
@@ -3433,14 +3886,15 @@ static void bfq_rq_enqueued(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 		 * is small and the queue is not to be expired, then
 		 * just exit.
 		 *
-		 * In this way, if the disk is being idled to wait for
-		 * a new request from the in-service queue, we avoid
-		 * unplugging the device and committing the disk to serve
-		 * just a small request. On the contrary, we wait for
-		 * the block layer to decide when to unplug the device:
-		 * hopefully, new requests will be merged to this one
-		 * quickly, then the device will be unplugged and
-		 * larger requests will be dispatched.
+		 * In this way, if the device is being idled to wait
+		 * for a new request from the in-service queue, we
+		 * avoid unplugging the device and committing the
+		 * device to serve just a small request. On the
+		 * contrary, we wait for the block layer to decide
+		 * when to unplug the device: hopefully, new requests
+		 * will be merged to this one quickly, then the device
+		 * will be unplugged and larger requests will be
+		 * dispatched.
 		 */
 		if (small_req && !budget_timeout)
 			return;
@@ -3453,9 +3907,7 @@ static void bfq_rq_enqueued(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 		 */
 		bfq_clear_bfqq_wait_request(bfqq);
 		del_timer(&bfqd->idle_slice_timer);
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
 		bfqg_stats_update_idle_time(bfqq_group(bfqq));
-#endif
 
 		/*
 		 * The queue is not empty, because a new request just
@@ -3499,27 +3951,19 @@ static void bfq_insert_request(struct request_queue *q, struct request *rq)
 			 */
 			new_bfqq->allocated[rq_data_dir(rq)]++;
 			bfqq->allocated[rq_data_dir(rq)]--;
-			atomic_inc(&new_bfqq->ref);
+			new_bfqq->ref++;
+			bfq_clear_bfqq_just_created(bfqq);
 			bfq_put_queue(bfqq);
 			if (bic_to_bfqq(RQ_BIC(rq), 1) == bfqq)
 				bfq_merge_bfqqs(bfqd, RQ_BIC(rq),
 						bfqq, new_bfqq);
 			rq->elv.priv[1] = new_bfqq;
 			bfqq = new_bfqq;
-		} else
-			bfq_bfqq_increase_failed_cooperations(bfqq);
+		}
 	}
 
 	bfq_add_request(rq);
 
-	/*
-	 * Here a newly-created bfq_queue has already started a weight-raising
-	 * period: clear raising_time_left to prevent bfq_bfqq_save_state()
-	 * from assigning it a full weight-raising period. See the detailed
-	 * comments about this field in bfq_init_icq().
-	 */
-	if (bfqq->bic)
-		bfqq->bic->wr_time_left = 0;
 	rq->fifo_time = jiffies + bfqd->bfq_fifo_expire[rq_is_sync(rq)];
 	list_add_tail(&rq->queuelist, &bfqq->fifo);
 
@@ -3528,8 +3972,8 @@ static void bfq_insert_request(struct request_queue *q, struct request *rq)
 
 static void bfq_update_hw_tag(struct bfq_data *bfqd)
 {
-	bfqd->max_rq_in_driver = max(bfqd->max_rq_in_driver,
-				     bfqd->rq_in_driver);
+	bfqd->max_rq_in_driver = max_t(int, bfqd->max_rq_in_driver,
+				       bfqd->rq_in_driver);
 
 	if (bfqd->hw_tag == 1)
 		return;
@@ -3555,48 +3999,45 @@ static void bfq_completed_request(struct request_queue *q, struct request *rq)
 {
 	struct bfq_queue *bfqq = RQ_BFQQ(rq);
 	struct bfq_data *bfqd = bfqq->bfqd;
-	bool sync = bfq_bfqq_sync(bfqq);
 
-	bfq_log_bfqq(bfqd, bfqq, "completed one req with %u sects left (%d)",
-		     blk_rq_sectors(rq), sync);
+	bfq_log_bfqq(bfqd, bfqq, "completed one req with %u sects left",
+		     blk_rq_sectors(rq));
 
+	assert_spin_locked(bfqd->queue->queue_lock);
 	bfq_update_hw_tag(bfqd);
 
 	BUG_ON(!bfqd->rq_in_driver);
 	BUG_ON(!bfqq->dispatched);
 	bfqd->rq_in_driver--;
 	bfqq->dispatched--;
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
 	bfqg_stats_update_completion(bfqq_group(bfqq),
 				     rq_start_time_ns(rq),
 				     rq_io_start_time_ns(rq), rq->cmd_flags);
-#endif
 
 	if (!bfqq->dispatched && !bfq_bfqq_busy(bfqq)) {
+		BUG_ON(!RB_EMPTY_ROOT(&bfqq->sort_list));
+		/*
+		 * Set budget_timeout (which we overload to store the
+		 * time at which the queue remains with no backlog and
+		 * no outstanding request; used by the weight-raising
+		 * mechanism).
+		 */
+		bfqq->budget_timeout = jiffies;
+
 		bfq_weights_tree_remove(bfqd, &bfqq->entity,
 					&bfqd->queue_weights_tree);
-		if (!blk_queue_nonrot(bfqd->queue)) {
-			BUG_ON(!bfqd->busy_in_flight_queues);
-			bfqd->busy_in_flight_queues--;
-			if (bfq_bfqq_constantly_seeky(bfqq)) {
-				BUG_ON(!bfqd->
-					const_seeky_busy_in_flight_queues);
-				bfqd->const_seeky_busy_in_flight_queues--;
-			}
-		}
 	}
 
-	if (sync) {
-		bfqd->sync_flight--;
-		RQ_BIC(rq)->ttime.last_end_request = jiffies;
-	}
+	RQ_BIC(rq)->ttime.last_end_request = jiffies;
 
 	/*
-	 * If we are waiting to discover whether the request pattern of the
-	 * task associated with the queue is actually isochronous, and
-	 * both requisites for this condition to hold are satisfied, then
-	 * compute soft_rt_next_start (see the comments to the function
-	 * bfq_bfqq_softrt_next_start()).
+	 * If we are waiting to discover whether the request pattern
+	 * of the task associated with the queue is actually
+	 * isochronous, and both requisites for this condition to hold
+	 * are now satisfied, then compute soft_rt_next_start (see the
+	 * comments on the function bfq_bfqq_softrt_next_start()). We
+	 * schedule this delayed check when bfqq expires, if it still
+	 * has in-flight requests.
 	 */
 	if (bfq_bfqq_softrt_update(bfqq) && bfqq->dispatched == 0 &&
 	    RB_EMPTY_ROOT(&bfqq->sort_list))
@@ -3608,10 +4049,7 @@ static void bfq_completed_request(struct request_queue *q, struct request *rq)
 	 * or if we want to idle in case it has no pending requests.
 	 */
 	if (bfqd->in_service_queue == bfqq) {
-		if (bfq_bfqq_budget_new(bfqq))
-			bfq_set_budget_timeout(bfqd);
-
-		if (bfq_bfqq_must_idle(bfqq)) {
+		if (bfqq->dispatched == 0 && bfq_bfqq_must_idle(bfqq)) {
 			bfq_arm_slice_timer(bfqd);
 			goto out;
 		} else if (bfq_may_expire_for_budg_timeout(bfqq))
@@ -3682,14 +4120,14 @@ static void bfq_put_request(struct request *rq)
 		rq->elv.priv[1] = NULL;
 
 		bfq_log_bfqq(bfqq->bfqd, bfqq, "put_request %p, %d",
-			     bfqq, atomic_read(&bfqq->ref));
+			     bfqq, bfqq->ref);
 		bfq_put_queue(bfqq);
 	}
 }
 
 /*
  * Returns NULL if a new bfqq should be allocated, or the old bfqq if this
- * was the last process referring to said bfqq.
+ * was the last process referring to that bfqq.
  */
 static struct bfq_queue *
 bfq_split_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq)
@@ -3727,11 +4165,8 @@ static int bfq_set_request(struct request_queue *q, struct request *rq,
 	unsigned long flags;
 	bool split = false;
 
-	might_sleep_if(gfpflags_allow_blocking(gfp_mask));
-
-	bfq_check_ioprio_change(bic, bio);
-
 	spin_lock_irqsave(q->queue_lock, flags);
+	bfq_check_ioprio_change(bic, bio);
 
 	if (!bic)
 		goto queue_fail;
@@ -3741,23 +4176,47 @@ static int bfq_set_request(struct request_queue *q, struct request *rq,
 new_queue:
 	bfqq = bic_to_bfqq(bic, is_sync);
 	if (!bfqq || bfqq == &bfqd->oom_bfqq) {
-		bfqq = bfq_get_queue(bfqd, bio, is_sync, bic, gfp_mask);
+		if (bfqq)
+			bfq_put_queue(bfqq);
+		bfqq = bfq_get_queue(bfqd, bio, is_sync, bic);
+		BUG_ON(!hlist_unhashed(&bfqq->burst_list_node));
+
 		bic_set_bfqq(bic, bfqq, is_sync);
 		if (split && is_sync) {
+			bfq_log_bfqq(bfqd, bfqq,
+				     "set_request: was_in_list %d "
+				     "was_in_large_burst %d "
+				     "large burst in progress %d",
+				     bic->was_in_burst_list,
+				     bic->saved_in_large_burst,
+				     bfqd->large_burst);
+
 			if ((bic->was_in_burst_list && bfqd->large_burst) ||
-			    bic->saved_in_large_burst)
+			    bic->saved_in_large_burst) {
+				bfq_log_bfqq(bfqd, bfqq,
+					     "set_request: marking in "
+					     "large burst");
 				bfq_mark_bfqq_in_large_burst(bfqq);
-			else {
-			    bfq_clear_bfqq_in_large_burst(bfqq);
-			    if (bic->was_in_burst_list)
-			       hlist_add_head(&bfqq->burst_list_node,
-				              &bfqd->burst_list);
+			} else {
+				bfq_log_bfqq(bfqd, bfqq,
+					     "set_request: clearing in "
+					     "large burst");
+				bfq_clear_bfqq_in_large_burst(bfqq);
+				if (bic->was_in_burst_list)
+					hlist_add_head(&bfqq->burst_list_node,
+						       &bfqd->burst_list);
 			}
+			bfqq->split_time = jiffies;
 		}
 	} else {
 		/* If the queue was seeky for too long, break it apart. */
 		if (bfq_bfqq_coop(bfqq) && bfq_bfqq_split_coop(bfqq)) {
 			bfq_log_bfqq(bfqd, bfqq, "breaking apart bfqq");
+
+			/* Update bic before losing reference to bfqq */
+			if (bfq_bfqq_in_large_burst(bfqq))
+				bic->saved_in_large_burst = true;
+
 			bfqq = bfq_split_bfqq(bic, bfqq);
 			split = true;
 			if (!bfqq)
@@ -3766,9 +4225,8 @@ new_queue:
 	}
 
 	bfqq->allocated[rw]++;
-	atomic_inc(&bfqq->ref);
-	bfq_log_bfqq(bfqd, bfqq, "set_request: bfqq %p, %d", bfqq,
-		     atomic_read(&bfqq->ref));
+	bfqq->ref++;
+	bfq_log_bfqq(bfqd, bfqq, "set_request: bfqq %p, %d", bfqq, bfqq->ref);
 
 	rq->elv.priv[0] = bic;
 	rq->elv.priv[1] = bfqq;
@@ -3783,7 +4241,6 @@ new_queue:
 	if (likely(bfqq != &bfqd->oom_bfqq) && bfqq_process_refs(bfqq) == 1) {
 		bfqq->bic = bic;
 		if (split) {
-			bfq_mark_bfqq_just_split(bfqq);
 			/*
 			 * If the queue has just been split from a shared
 			 * queue, restore the idle window and the possible
@@ -3793,6 +4250,9 @@ new_queue:
 		}
 	}
 
+	if (unlikely(bfq_bfqq_just_created(bfqq)))
+		bfq_handle_burst(bfqd, bfqq);
+
 	spin_unlock_irqrestore(q->queue_lock, flags);
 
 	return 0;
@@ -3872,6 +4332,7 @@ static void bfq_shutdown_timer_wq(struct bfq_data *bfqd)
 	cancel_work_sync(&bfqd->unplug_work);
 }
 
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
 static void __bfq_put_async_bfqq(struct bfq_data *bfqd,
 					struct bfq_queue **bfqq_ptr)
 {
@@ -3880,9 +4341,9 @@ static void __bfq_put_async_bfqq(struct bfq_data *bfqd,
 
 	bfq_log(bfqd, "put_async_bfqq: %p", bfqq);
 	if (bfqq) {
-		bfq_bfqq_move(bfqd, bfqq, &bfqq->entity, root_group);
+		bfq_bfqq_move(bfqd, bfqq, root_group);
 		bfq_log_bfqq(bfqd, bfqq, "put_async_bfqq: putting %p, %d",
-			     bfqq, atomic_read(&bfqq->ref));
+			     bfqq, bfqq->ref);
 		bfq_put_queue(bfqq);
 		*bfqq_ptr = NULL;
 	}
@@ -3904,6 +4365,7 @@ static void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg)
 
 	__bfq_put_async_bfqq(bfqd, &bfqg->async_idle_bfqq);
 }
+#endif
 
 static void bfq_exit_queue(struct elevator_queue *e)
 {
@@ -3923,8 +4385,6 @@ static void bfq_exit_queue(struct elevator_queue *e)
 
 	bfq_shutdown_timer_wq(bfqd);
 
-	synchronize_rcu();
-
 	BUG_ON(timer_pending(&bfqd->idle_slice_timer));
 
 #ifdef CONFIG_BFQ_GROUP_IOSCHED
@@ -3973,11 +4433,14 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
 	 * will not attempt to free it.
 	 */
 	bfq_init_bfqq(bfqd, &bfqd->oom_bfqq, NULL, 1, 0);
-	atomic_inc(&bfqd->oom_bfqq.ref);
+	bfqd->oom_bfqq.ref++;
 	bfqd->oom_bfqq.new_ioprio = BFQ_DEFAULT_QUEUE_IOPRIO;
 	bfqd->oom_bfqq.new_ioprio_class = IOPRIO_CLASS_BE;
 	bfqd->oom_bfqq.entity.new_weight =
 		bfq_ioprio_to_weight(bfqd->oom_bfqq.new_ioprio);
+
+	/* oom_bfqq does not participate to bursts */
+	bfq_clear_bfqq_just_created(&bfqd->oom_bfqq);
 	/*
 	 * Trigger weight initialization, according to ioprio, at the
 	 * oom_bfqq's first activation. The oom_bfqq's ioprio and ioprio
@@ -3996,9 +4459,6 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
 		goto out_free;
 	bfq_init_root_group(bfqd->root_group, bfqd);
 	bfq_init_entity(&bfqd->oom_bfqq.entity, bfqd->root_group);
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
-	bfqd->active_numerous_groups = 0;
-#endif
 
 	init_timer(&bfqd->idle_slice_timer);
 	bfqd->idle_slice_timer.function = bfq_idle_slice_timer;
@@ -4023,20 +4483,19 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
 	bfqd->bfq_back_penalty = bfq_back_penalty;
 	bfqd->bfq_slice_idle = bfq_slice_idle;
 	bfqd->bfq_class_idle_last_service = 0;
-	bfqd->bfq_max_budget_async_rq = bfq_max_budget_async_rq;
-	bfqd->bfq_timeout[BLK_RW_ASYNC] = bfq_timeout_async;
-	bfqd->bfq_timeout[BLK_RW_SYNC] = bfq_timeout_sync;
+	bfqd->bfq_timeout = bfq_timeout;
 
-	bfqd->bfq_coop_thresh = 2;
-	bfqd->bfq_failed_cooperations = 7000;
 	bfqd->bfq_requests_within_timer = 120;
 
-	bfqd->bfq_large_burst_thresh = 11;
-	bfqd->bfq_burst_interval = msecs_to_jiffies(500);
+	bfqd->bfq_large_burst_thresh = 8;
+	bfqd->bfq_burst_interval = msecs_to_jiffies(180);
 
 	bfqd->low_latency = true;
 
-	bfqd->bfq_wr_coeff = 20;
+	/*
+	 * Trade-off between responsiveness and fairness.
+	 */
+	bfqd->bfq_wr_coeff = 30;
 	bfqd->bfq_wr_rt_max_time = msecs_to_jiffies(300);
 	bfqd->bfq_wr_max_time = 0;
 	bfqd->bfq_wr_min_idle_time = msecs_to_jiffies(2000);
@@ -4048,16 +4507,15 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
 					      * video.
 					      */
 	bfqd->wr_busy_queues = 0;
-	bfqd->busy_in_flight_queues = 0;
-	bfqd->const_seeky_busy_in_flight_queues = 0;
 
 	/*
-	 * Begin by assuming, optimistically, that the device peak rate is
-	 * equal to the highest reference rate.
+	 * Begin by assuming, optimistically, that the device is a
+	 * high-speed one, and that its peak rate is equal to 2/3 of
+	 * the highest reference rate.
 	 */
 	bfqd->RT_prod = R_fast[blk_queue_nonrot(bfqd->queue)] *
 			T_fast[blk_queue_nonrot(bfqd->queue)];
-	bfqd->peak_rate = R_fast[blk_queue_nonrot(bfqd->queue)];
+	bfqd->peak_rate = R_fast[blk_queue_nonrot(bfqd->queue)] * 2 / 3;
 	bfqd->device_speed = BFQ_BFQD_FAST;
 
 	return 0;
@@ -4161,10 +4619,8 @@ SHOW_FUNCTION(bfq_back_seek_max_show, bfqd->bfq_back_max, 0);
 SHOW_FUNCTION(bfq_back_seek_penalty_show, bfqd->bfq_back_penalty, 0);
 SHOW_FUNCTION(bfq_slice_idle_show, bfqd->bfq_slice_idle, 1);
 SHOW_FUNCTION(bfq_max_budget_show, bfqd->bfq_user_max_budget, 0);
-SHOW_FUNCTION(bfq_max_budget_async_rq_show,
-	      bfqd->bfq_max_budget_async_rq, 0);
-SHOW_FUNCTION(bfq_timeout_sync_show, bfqd->bfq_timeout[BLK_RW_SYNC], 1);
-SHOW_FUNCTION(bfq_timeout_async_show, bfqd->bfq_timeout[BLK_RW_ASYNC], 1);
+SHOW_FUNCTION(bfq_timeout_sync_show, bfqd->bfq_timeout, 1);
+SHOW_FUNCTION(bfq_strict_guarantees_show, bfqd->strict_guarantees, 0);
 SHOW_FUNCTION(bfq_low_latency_show, bfqd->low_latency, 0);
 SHOW_FUNCTION(bfq_wr_coeff_show, bfqd->bfq_wr_coeff, 0);
 SHOW_FUNCTION(bfq_wr_rt_max_time_show, bfqd->bfq_wr_rt_max_time, 1);
@@ -4199,10 +4655,6 @@ STORE_FUNCTION(bfq_back_seek_max_store, &bfqd->bfq_back_max, 0, INT_MAX, 0);
 STORE_FUNCTION(bfq_back_seek_penalty_store, &bfqd->bfq_back_penalty, 1,
 		INT_MAX, 0);
 STORE_FUNCTION(bfq_slice_idle_store, &bfqd->bfq_slice_idle, 0, INT_MAX, 1);
-STORE_FUNCTION(bfq_max_budget_async_rq_store, &bfqd->bfq_max_budget_async_rq,
-		1, INT_MAX, 0);
-STORE_FUNCTION(bfq_timeout_async_store, &bfqd->bfq_timeout[BLK_RW_ASYNC], 0,
-		INT_MAX, 1);
 STORE_FUNCTION(bfq_wr_coeff_store, &bfqd->bfq_wr_coeff, 1, INT_MAX, 0);
 STORE_FUNCTION(bfq_wr_max_time_store, &bfqd->bfq_wr_max_time, 0, INT_MAX, 1);
 STORE_FUNCTION(bfq_wr_rt_max_time_store, &bfqd->bfq_wr_rt_max_time, 0, INT_MAX,
@@ -4224,10 +4676,8 @@ static ssize_t bfq_weights_store(struct elevator_queue *e,
 
 static unsigned long bfq_estimated_max_budget(struct bfq_data *bfqd)
 {
-	u64 timeout = jiffies_to_msecs(bfqd->bfq_timeout[BLK_RW_SYNC]);
-
 	if (bfqd->peak_rate_samples >= BFQ_PEAK_RATE_SAMPLES)
-		return bfq_calc_max_budget(bfqd->peak_rate, timeout);
+		return bfq_calc_max_budget(bfqd);
 	else
 		return bfq_default_max_budget;
 }
@@ -4252,6 +4702,10 @@ static ssize_t bfq_max_budget_store(struct elevator_queue *e,
 	return ret;
 }
 
+/* 
+ * Leaving this name to preserve name compatibility with cfq
+ * parameters, but this timeout is used for both sync and async.
+ */
 static ssize_t bfq_timeout_sync_store(struct elevator_queue *e,
 				      const char *page, size_t count)
 {
@@ -4264,13 +4718,31 @@ static ssize_t bfq_timeout_sync_store(struct elevator_queue *e,
 	else if (__data > INT_MAX)
 		__data = INT_MAX;
 
-	bfqd->bfq_timeout[BLK_RW_SYNC] = msecs_to_jiffies(__data);
+	bfqd->bfq_timeout = msecs_to_jiffies(__data);
 	if (bfqd->bfq_user_max_budget == 0)
 		bfqd->bfq_max_budget = bfq_estimated_max_budget(bfqd);
 
 	return ret;
 }
 
+static ssize_t bfq_strict_guarantees_store(struct elevator_queue *e,
+				     const char *page, size_t count)
+{
+	struct bfq_data *bfqd = e->elevator_data;
+	unsigned long uninitialized_var(__data);
+	int ret = bfq_var_store(&__data, (page), count);
+
+	if (__data > 1)
+		__data = 1;
+	if (!bfqd->strict_guarantees && __data == 1
+	    && bfqd->bfq_slice_idle < msecs_to_jiffies(8))
+		bfqd->bfq_slice_idle = msecs_to_jiffies(8);
+
+	bfqd->strict_guarantees = __data;
+
+	return ret;
+}
+
 static ssize_t bfq_low_latency_store(struct elevator_queue *e,
 				     const char *page, size_t count)
 {
@@ -4297,9 +4769,8 @@ static struct elv_fs_entry bfq_attrs[] = {
 	BFQ_ATTR(back_seek_penalty),
 	BFQ_ATTR(slice_idle),
 	BFQ_ATTR(max_budget),
-	BFQ_ATTR(max_budget_async_rq),
 	BFQ_ATTR(timeout_sync),
-	BFQ_ATTR(timeout_async),
+	BFQ_ATTR(strict_guarantees),
 	BFQ_ATTR(low_latency),
 	BFQ_ATTR(wr_coeff),
 	BFQ_ATTR(wr_max_time),
@@ -4342,9 +4813,28 @@ static struct elevator_type iosched_bfq = {
 	.elevator_owner =	THIS_MODULE,
 };
 
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+static struct blkcg_policy blkcg_policy_bfq = {
+	.dfl_cftypes		= bfq_blkg_files,
+	.legacy_cftypes		= bfq_blkcg_legacy_files,
+
+	.cpd_alloc_fn		= bfq_cpd_alloc,
+	.cpd_init_fn		= bfq_cpd_init,
+	.cpd_bind_fn	        = bfq_cpd_init,
+	.cpd_free_fn		= bfq_cpd_free,
+
+	.pd_alloc_fn		= bfq_pd_alloc,
+	.pd_init_fn		= bfq_pd_init,
+	.pd_offline_fn		= bfq_pd_offline,
+	.pd_free_fn		= bfq_pd_free,
+	.pd_reset_stats_fn	= bfq_pd_reset_stats,
+};
+#endif
+
 static int __init bfq_init(void)
 {
 	int ret;
+	char msg[50] = "BFQ I/O-scheduler: v8r3";
 
 	/*
 	 * Can be 0 on HZ < 1000 setups.
@@ -4352,9 +4842,6 @@ static int __init bfq_init(void)
 	if (bfq_slice_idle == 0)
 		bfq_slice_idle = 1;
 
-	if (bfq_timeout_async == 0)
-		bfq_timeout_async = 1;
-
 #ifdef CONFIG_BFQ_GROUP_IOSCHED
 	ret = blkcg_policy_register(&blkcg_policy_bfq);
 	if (ret)
@@ -4370,23 +4857,34 @@ static int __init bfq_init(void)
 	 * installed on the reference devices (see the comments before the
 	 * definitions of the two arrays).
 	 */
-	T_slow[0] = msecs_to_jiffies(2600);
-	T_slow[1] = msecs_to_jiffies(1000);
-	T_fast[0] = msecs_to_jiffies(5500);
-	T_fast[1] = msecs_to_jiffies(2000);
+	T_slow[0] = msecs_to_jiffies(3500);
+	T_slow[1] = msecs_to_jiffies(1500);
+	T_fast[0] = msecs_to_jiffies(8000);
+	T_fast[1] = msecs_to_jiffies(3000);
 
 	/*
-	 * Thresholds that determine the switch between speed classes (see
-	 * the comments before the definition of the array).
+	 * Thresholds that determine the switch between speed classes
+	 * (see the comments before the definition of the array
+	 * device_speed_thresh). These thresholds are biased towards
+	 * transitions to the fast class. This is safer than the
+	 * opposite bias. In fact, a wrong transition to the slow
+	 * class results in short weight-raising periods, because the
+	 * speed of the device then tends to be higher that the
+	 * reference peak rate. On the opposite end, a wrong
+	 * transition to the fast class tends to increase
+	 * weight-raising periods, because of the opposite reason.
 	 */
-	device_speed_thresh[0] = (R_fast[0] + R_slow[0]) / 2;
-	device_speed_thresh[1] = (R_fast[1] + R_slow[1]) / 2;
+	device_speed_thresh[0] = (4 * R_slow[0]) / 3;
+	device_speed_thresh[1] = (4 * R_slow[1]) / 3;
 
 	ret = elv_register(&iosched_bfq);
 	if (ret)
 		goto err_pol_unreg;
 
-	pr_info("BFQ I/O-scheduler: v7r11");
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+	strcat(msg, " (with cgroups support)");
+#endif
+	pr_info("%s", msg);
 
 	return 0;
 
diff --git a/block/bfq-sched.c b/block/bfq-sched.c
index a64fec1197f7..7d73b9de1409 100644
--- a/block/bfq-sched.c
+++ b/block/bfq-sched.c
@@ -7,9 +7,11 @@
  * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
  *		      Paolo Valente <paolo.valente@unimore.it>
  *
- * Copyright (C) 2010 Paolo Valente <paolo.valente@unimore.it>
+ * Copyright (C) 2016 Paolo Valente <paolo.valente@unimore.it>
  */
 
+static struct bfq_group *bfqq_group(struct bfq_queue *bfqq);
+
 #ifdef CONFIG_BFQ_GROUP_IOSCHED
 #define for_each_entity(entity)	\
 	for (; entity ; entity = entity->parent)
@@ -22,8 +24,6 @@ static struct bfq_entity *bfq_lookup_next_entity(struct bfq_sched_data *sd,
 						 int extract,
 						 struct bfq_data *bfqd);
 
-static struct bfq_group *bfqq_group(struct bfq_queue *bfqq);
-
 static void bfq_update_budget(struct bfq_entity *next_in_service)
 {
 	struct bfq_entity *bfqg_entity;
@@ -48,6 +48,7 @@ static void bfq_update_budget(struct bfq_entity *next_in_service)
 static int bfq_update_next_in_service(struct bfq_sched_data *sd)
 {
 	struct bfq_entity *next_in_service;
+	struct bfq_queue *bfqq;
 
 	if (sd->in_service_entity)
 		/* will update/requeue at the end of service */
@@ -65,14 +66,29 @@ static int bfq_update_next_in_service(struct bfq_sched_data *sd)
 
 	if (next_in_service)
 		bfq_update_budget(next_in_service);
+	else
+		goto exit;
 
+	bfqq = bfq_entity_to_bfqq(next_in_service);
+	if (bfqq)
+		bfq_log_bfqq(bfqq->bfqd, bfqq,
+			     "update_next_in_service: chosen this queue");
+	else {
+		struct bfq_group *bfqg =
+			container_of(next_in_service,
+				     struct bfq_group, entity);
+
+		bfq_log_bfqg((struct bfq_data *)bfqg->bfqd, bfqg,
+			     "update_next_in_service: chosen this entity");
+	}
+exit:
 	return 1;
 }
 
 static void bfq_check_next_in_service(struct bfq_sched_data *sd,
 				      struct bfq_entity *entity)
 {
-	BUG_ON(sd->next_in_service != entity);
+	WARN_ON(sd->next_in_service != entity);
 }
 #else
 #define for_each_entity(entity)	\
@@ -151,20 +167,35 @@ static u64 bfq_delta(unsigned long service, unsigned long weight)
 static void bfq_calc_finish(struct bfq_entity *entity, unsigned long service)
 {
 	struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
-
+	unsigned long long start, finish, delta ;
 	BUG_ON(entity->weight == 0);
 
 	entity->finish = entity->start +
 		bfq_delta(service, entity->weight);
 
+	start = ((entity->start>>10)*1000)>>12;
+	finish = ((entity->finish>>10)*1000)>>12;
+	delta = ((bfq_delta(service, entity->weight)>>10)*1000)>>12;
+
 	if (bfqq) {
 		bfq_log_bfqq(bfqq->bfqd, bfqq,
 			"calc_finish: serv %lu, w %d",
 			service, entity->weight);
 		bfq_log_bfqq(bfqq->bfqd, bfqq,
 			"calc_finish: start %llu, finish %llu, delta %llu",
-			entity->start, entity->finish,
-			bfq_delta(service, entity->weight));
+			start, finish, delta);
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+	} else {
+		struct bfq_group *bfqg =
+			container_of(entity, struct bfq_group, entity);
+
+		bfq_log_bfqg((struct bfq_data *)bfqg->bfqd, bfqg,
+			"calc_finish group: serv %lu, w %d",
+			     service, entity->weight);
+		bfq_log_bfqg((struct bfq_data *)bfqg->bfqd, bfqg,
+			"calc_finish group: start %llu, finish %llu, delta %llu",
+			start, finish, delta);
+#endif
 	}
 }
 
@@ -386,8 +417,6 @@ static void bfq_active_insert(struct bfq_service_tree *st,
 		BUG_ON(!bfqg);
 		BUG_ON(!bfqd);
 		bfqg->active_entities++;
-		if (bfqg->active_entities == 2)
-			bfqd->active_numerous_groups++;
 	}
 #endif
 }
@@ -399,7 +428,7 @@ static void bfq_active_insert(struct bfq_service_tree *st,
 static unsigned short bfq_ioprio_to_weight(int ioprio)
 {
 	BUG_ON(ioprio < 0 || ioprio >= IOPRIO_BE_NR);
-	return IOPRIO_BE_NR * BFQ_WEIGHT_CONVERSION_COEFF - ioprio;
+	return (IOPRIO_BE_NR - ioprio) * BFQ_WEIGHT_CONVERSION_COEFF ;
 }
 
 /**
@@ -422,9 +451,9 @@ static void bfq_get_entity(struct bfq_entity *entity)
 	struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
 
 	if (bfqq) {
-		atomic_inc(&bfqq->ref);
+		bfqq->ref++;
 		bfq_log_bfqq(bfqq->bfqd, bfqq, "get_entity: %p %d",
-			     bfqq, atomic_read(&bfqq->ref));
+			     bfqq, bfqq->ref);
 	}
 }
 
@@ -499,10 +528,6 @@ static void bfq_active_extract(struct bfq_service_tree *st,
 		BUG_ON(!bfqd);
 		BUG_ON(!bfqg->active_entities);
 		bfqg->active_entities--;
-		if (bfqg->active_entities == 1) {
-			BUG_ON(!bfqd->active_numerous_groups);
-			bfqd->active_numerous_groups--;
-		}
 	}
 #endif
 }
@@ -552,7 +577,7 @@ static void bfq_forget_entity(struct bfq_service_tree *st,
 	if (bfqq) {
 		sd = entity->sched_data;
 		bfq_log_bfqq(bfqq->bfqd, bfqq, "forget_entity: %p %d",
-			     bfqq, atomic_read(&bfqq->ref));
+			     bfqq, bfqq->ref);
 		bfq_put_queue(bfqq);
 	}
 }
@@ -602,7 +627,7 @@ __bfq_entity_update_weight_prio(struct bfq_service_tree *old_st,
 
 	if (entity->prio_changed) {
 		struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
-		unsigned short prev_weight, new_weight;
+		unsigned int prev_weight, new_weight;
 		struct bfq_data *bfqd = NULL;
 		struct rb_root *root;
 #ifdef CONFIG_BFQ_GROUP_IOSCHED
@@ -628,12 +653,14 @@ __bfq_entity_update_weight_prio(struct bfq_service_tree *old_st,
 		if (entity->new_weight != entity->orig_weight) {
 			if (entity->new_weight < BFQ_MIN_WEIGHT ||
 			    entity->new_weight > BFQ_MAX_WEIGHT) {
-				printk(KERN_CRIT "update_weight_prio: "
-						 "new_weight %d\n",
+				pr_crit("update_weight_prio: new_weight %d\n",
 					entity->new_weight);
-				BUG();
+				if (entity->new_weight < BFQ_MIN_WEIGHT)
+					entity->new_weight = BFQ_MIN_WEIGHT;
+				else
+					entity->new_weight = BFQ_MAX_WEIGHT;
 			}
-			entity->orig_weight = entity->new_weight;
+		       	entity->orig_weight = entity->new_weight;
 			if (bfqq)
 				bfqq->ioprio =
 				  bfq_weight_to_ioprio(entity->orig_weight);
@@ -662,6 +689,13 @@ __bfq_entity_update_weight_prio(struct bfq_service_tree *old_st,
 		 * associated with its new weight.
 		 */
 		if (prev_weight != new_weight) {
+			if (bfqq)
+				bfq_log_bfqq(bfqq->bfqd, bfqq,
+					     "weight changed %d %d(%d %d)",
+					     prev_weight, new_weight,
+					     entity->orig_weight,
+					     bfqq->wr_coeff);
+
 			root = bfqq ? &bfqd->queue_weights_tree :
 				      &bfqd->group_weights_tree;
 			bfq_weights_tree_remove(bfqd, entity, root);
@@ -708,7 +742,7 @@ static void bfq_bfqq_served(struct bfq_queue *bfqq, int served)
 		st = bfq_entity_service_tree(entity);
 
 		entity->service += served;
-		BUG_ON(entity->service > entity->budget);
+
 		BUG_ON(st->wsum == 0);
 
 		st->vtime += bfq_delta(served, st->wsum);
@@ -717,31 +751,69 @@ static void bfq_bfqq_served(struct bfq_queue *bfqq, int served)
 #ifdef CONFIG_BFQ_GROUP_IOSCHED
 	bfqg_stats_set_start_empty_time(bfqq_group(bfqq));
 #endif
-	bfq_log_bfqq(bfqq->bfqd, bfqq, "bfqq_served %d secs", served);
+	st = bfq_entity_service_tree(&bfqq->entity);
+	bfq_log_bfqq(bfqq->bfqd, bfqq, "bfqq_served %d secs, vtime %llu on %p",
+		     served,  ((st->vtime>>10)*1000)>>12, st);
 }
 
 /**
- * bfq_bfqq_charge_full_budget - set the service to the entity budget.
+ * bfq_bfqq_charge_time - charge an amount of service equivalent to the length
+ *			  of the time interval during which bfqq has been in
+ *			  service.
+ * @bfqd: the device
  * @bfqq: the queue that needs a service update.
+ * @time_ms: the amount of time during which the queue has received service
  *
- * When it's not possible to be fair in the service domain, because
- * a queue is not consuming its budget fast enough (the meaning of
- * fast depends on the timeout parameter), we charge it a full
- * budget.  In this way we should obtain a sort of time-domain
- * fairness among all the seeky/slow queues.
+ * If a queue does not consume its budget fast enough, then providing
+ * the queue with service fairness may impair throughput, more or less
+ * severely. For this reason, queues that consume their budget slowly
+ * are provided with time fairness instead of service fairness. This
+ * goal is achieved through the BFQ scheduling engine, even if such an
+ * engine works in the service, and not in the time domain. The trick
+ * is charging these queues with an inflated amount of service, equal
+ * to the amount of service that they would have received during their
+ * service slot if they had been fast, i.e., if their requests had
+ * been dispatched at a rate equal to the estimated peak rate.
+ *
+ * It is worth noting that time fairness can cause important
+ * distortions in terms of bandwidth distribution, on devices with
+ * internal queueing. The reason is that I/O requests dispatched
+ * during the service slot of a queue may be served after that service
+ * slot is finished, and may have a total processing time loosely
+ * correlated with the duration of the service slot. This is
+ * especially true for short service slots.
  */
-static void bfq_bfqq_charge_full_budget(struct bfq_queue *bfqq)
+static void bfq_bfqq_charge_time(struct bfq_data *bfqd, struct bfq_queue *bfqq,
+				 unsigned long time_ms)
 {
 	struct bfq_entity *entity = &bfqq->entity;
+	int tot_serv_to_charge = entity->service;
+	unsigned int timeout_ms = jiffies_to_msecs(bfq_timeout);
 
-	bfq_log_bfqq(bfqq->bfqd, bfqq, "charge_full_budget");
+	if (time_ms > 0 && time_ms < timeout_ms)
+		tot_serv_to_charge =
+			(bfqd->bfq_max_budget * time_ms) / timeout_ms;
 
-	bfq_bfqq_served(bfqq, entity->budget - entity->service);
+	if (tot_serv_to_charge < entity->service)
+		tot_serv_to_charge = entity->service;
+
+	bfq_log_bfqq(bfqq->bfqd, bfqq,
+		     "charge_time: %lu/%u ms, %d/%d/%d sectors",
+		     time_ms, timeout_ms, entity->service,
+		     tot_serv_to_charge, entity->budget);
+
+	/* Increase budget to avoid inconsistencies */
+	if (tot_serv_to_charge > entity->budget)
+		entity->budget = tot_serv_to_charge;
+
+	bfq_bfqq_served(bfqq,
+			max_t(int, 0, tot_serv_to_charge - entity->service));
 }
 
 /**
  * __bfq_activate_entity - activate an entity.
  * @entity: the entity being activated.
+ * @non_blocking_wait_rq: true if this entity was waiting for a request
  *
  * Called whenever an entity is activated, i.e., it is not active and one
  * of its children receives a new request, or has to be reactivated due to
@@ -749,11 +821,16 @@ static void bfq_bfqq_charge_full_budget(struct bfq_queue *bfqq)
  * service received if @entity is active) of the queue to calculate its
  * timestamps.
  */
-static void __bfq_activate_entity(struct bfq_entity *entity)
+static void __bfq_activate_entity(struct bfq_entity *entity,
+				  bool non_blocking_wait_rq)
 {
 	struct bfq_sched_data *sd = entity->sched_data;
 	struct bfq_service_tree *st = bfq_entity_service_tree(entity);
+	struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
+	bool backshifted = false;
 
+	BUG_ON(!sd);
+	BUG_ON(!st);
 	if (entity == sd->in_service_entity) {
 		BUG_ON(entity->tree);
 		/*
@@ -771,45 +848,133 @@ static void __bfq_activate_entity(struct bfq_entity *entity)
 		 * old start time.
 		 */
 		bfq_active_extract(st, entity);
-	} else if (entity->tree == &st->idle) {
-		/*
-		 * Must be on the idle tree, bfq_idle_extract() will
-		 * check for that.
-		 */
-		bfq_idle_extract(st, entity);
-		entity->start = bfq_gt(st->vtime, entity->finish) ?
-				       st->vtime : entity->finish;
 	} else {
-		/*
-		 * The finish time of the entity may be invalid, and
-		 * it is in the past for sure, otherwise the queue
-		 * would have been on the idle tree.
-		 */
-		entity->start = st->vtime;
-		st->wsum += entity->weight;
-		bfq_get_entity(entity);
+		unsigned long long min_vstart;
 
-		BUG_ON(entity->on_st);
-		entity->on_st = 1;
+		/* See comments on bfq_fqq_update_budg_for_activation */
+		if (non_blocking_wait_rq && bfq_gt(st->vtime, entity->finish)) {
+			backshifted = true;
+			min_vstart = entity->finish;
+		} else
+			min_vstart = st->vtime;
+
+		if (entity->tree == &st->idle) {
+			/*
+			 * Must be on the idle tree, bfq_idle_extract() will
+			 * check for that.
+			 */
+			bfq_idle_extract(st, entity);
+			entity->start = bfq_gt(min_vstart, entity->finish) ?
+				min_vstart : entity->finish;
+		} else {
+			/*
+			 * The finish time of the entity may be invalid, and
+			 * it is in the past for sure, otherwise the queue
+			 * would have been on the idle tree.
+			 */
+			entity->start = min_vstart;
+			st->wsum += entity->weight;
+			bfq_get_entity(entity);
+
+			BUG_ON(entity->on_st);
+			entity->on_st = 1;
+		}
 	}
 
 	st = __bfq_entity_update_weight_prio(st, entity);
 	bfq_calc_finish(entity, entity->budget);
+
+	/*
+	 * If some queues enjoy backshifting for a while, then their
+	 * (virtual) finish timestamps may happen to become lower and
+	 * lower than the system virtual time.  In particular, if
+	 * these queues often happen to be idle for short time
+	 * periods, and during such time periods other queues with
+	 * higher timestamps happen to be busy, then the backshifted
+	 * timestamps of the former queues can become much lower than
+	 * the system virtual time. In fact, to serve the queues with
+	 * higher timestamps while the ones with lower timestamps are
+	 * idle, the system virtual time may be pushed-up to much
+	 * higher values than the finish timestamps of the idle
+	 * queues. As a consequence, the finish timestamps of all new
+	 * or newly activated queues may end up being much larger than
+	 * those of lucky queues with backshifted timestamps. The
+	 * latter queues may then monopolize the device for a lot of
+	 * time. This would simply break service guarantees.
+	 *
+	 * To reduce this problem, push up a little bit the
+	 * backshifted timestamps of the queue associated with this
+	 * entity (only a queue can happen to have the backshifted
+	 * flag set): just enough to let the finish timestamp of the
+	 * queue be equal to the current value of the system virtual
+	 * time. This may introduce a little unfairness among queues
+	 * with backshifted timestamps, but it does not break
+	 * worst-case fairness guarantees.
+	 *
+	 * As a special case, if bfqq is weight-raised, push up
+	 * timestamps much less, to keep very low the probability that
+	 * this push up causes the backshifted finish timestamps of
+	 * weight-raised queues to become higher than the backshifted
+	 * finish timestamps of non weight-raised queues.
+	 */
+	if (backshifted && bfq_gt(st->vtime, entity->finish)) {
+		unsigned long delta = st->vtime - entity->finish;
+
+		if (bfqq)
+			delta /= bfqq->wr_coeff;
+
+		entity->start += delta;
+		entity->finish += delta;
+
+		if (bfqq) {
+			bfq_log_bfqq(bfqq->bfqd, bfqq,
+				     "__activate_entity: new queue finish %llu",
+				     ((entity->finish>>10)*1000)>>12);
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+		} else {
+			struct bfq_group *bfqg =
+				container_of(entity, struct bfq_group, entity);
+
+			bfq_log_bfqg((struct bfq_data *)bfqg->bfqd, bfqg,
+				     "__activate_entity: new group finish %llu",
+				     ((entity->finish>>10)*1000)>>12);
+#endif
+		}
+	}
+
 	bfq_active_insert(st, entity);
+
+	if (bfqq) {
+		bfq_log_bfqq(bfqq->bfqd, bfqq,
+			"__activate_entity: queue %seligible in st %p",
+			     entity->start <= st->vtime ? "" : "non ", st);
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+	} else {
+		struct bfq_group *bfqg =
+			container_of(entity, struct bfq_group, entity);
+
+		bfq_log_bfqg((struct bfq_data *)bfqg->bfqd, bfqg,
+			"__activate_entity: group %seligible in st %p",
+			     entity->start <= st->vtime ? "" : "non ", st);
+#endif
+	}
 }
 
 /**
  * bfq_activate_entity - activate an entity and its ancestors if necessary.
  * @entity: the entity to activate.
+ * @non_blocking_wait_rq: true if this entity was waiting for a request
  *
  * Activate @entity and all the entities on the path from it to the root.
  */
-static void bfq_activate_entity(struct bfq_entity *entity)
+static void bfq_activate_entity(struct bfq_entity *entity,
+				bool non_blocking_wait_rq)
 {
 	struct bfq_sched_data *sd;
 
 	for_each_entity(entity) {
-		__bfq_activate_entity(entity);
+		BUG_ON(!entity);
+		__bfq_activate_entity(entity, non_blocking_wait_rq);
 
 		sd = entity->sched_data;
 		if (!bfq_update_next_in_service(sd))
@@ -890,23 +1055,24 @@ static void bfq_deactivate_entity(struct bfq_entity *entity, int requeue)
 
 		if (!__bfq_deactivate_entity(entity, requeue))
 			/*
-			 * The parent entity is still backlogged, and
-			 * we don't need to update it as it is still
-			 * in service.
+			 * next_in_service has not been changed, so
+			 * no upwards update is needed
 			 */
 			break;
 
 		if (sd->next_in_service)
 			/*
-			 * The parent entity is still backlogged and
-			 * the budgets on the path towards the root
-			 * need to be updated.
+			 * The parent entity is still backlogged,
+			 * because next_in_service is not NULL, and
+			 * next_in_service has been updated (see
+			 * comment on the body of the above if):
+			 * upwards update of the schedule is needed.
 			 */
 			goto update;
 
 		/*
-		 * If we reach there the parent is no more backlogged and
-		 * we want to propagate the dequeue upwards.
+		 * If we get here, then the parent is no more backlogged and
+		 * we want to propagate the deactivation upwards.
 		 */
 		requeue = 1;
 	}
@@ -916,9 +1082,23 @@ static void bfq_deactivate_entity(struct bfq_entity *entity, int requeue)
 update:
 	entity = parent;
 	for_each_entity(entity) {
-		__bfq_activate_entity(entity);
+		struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
+		__bfq_activate_entity(entity, false);
 
 		sd = entity->sched_data;
+		if (bfqq)
+			bfq_log_bfqq(bfqq->bfqd, bfqq,
+				     "invoking udpdate_next for this queue");
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+		else {
+			struct bfq_group *bfqg =
+				container_of(entity,
+					     struct bfq_group, entity);
+
+			bfq_log_bfqg((struct bfq_data *)bfqg->bfqd, bfqg,
+				     "invoking udpdate_next for this entity");
+		}
+#endif
 		if (!bfq_update_next_in_service(sd))
 			break;
 	}
@@ -997,10 +1177,11 @@ left:
  * Update the virtual time in @st and return the first eligible entity
  * it contains.
  */
-static struct bfq_entity *__bfq_lookup_next_entity(struct bfq_service_tree *st,
-						   bool force)
+static struct bfq_entity *
+__bfq_lookup_next_entity(struct bfq_service_tree *st, bool force)
 {
 	struct bfq_entity *entity, *new_next_in_service = NULL;
+	struct bfq_queue *bfqq;
 
 	if (RB_EMPTY_ROOT(&st->active))
 		return NULL;
@@ -1009,6 +1190,24 @@ static struct bfq_entity *__bfq_lookup_next_entity(struct bfq_service_tree *st,
 	entity = bfq_first_active_entity(st);
 	BUG_ON(bfq_gt(entity->start, st->vtime));
 
+	bfqq = bfq_entity_to_bfqq(entity);
+	if (bfqq)
+		bfq_log_bfqq(bfqq->bfqd, bfqq,
+			     "__lookup_next: start %llu vtime %llu st %p",
+			     ((entity->start>>10)*1000)>>12,
+			     ((st->vtime>>10)*1000)>>12, st);
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+	else {
+		struct bfq_group *bfqg =
+			container_of(entity, struct bfq_group, entity);
+
+		bfq_log_bfqg((struct bfq_data *)bfqg->bfqd, bfqg,
+			     "__lookup_next: start %llu vtime %llu st %p",
+			     ((entity->start>>10)*1000)>>12,
+			     ((st->vtime>>10)*1000)>>12, st);
+	}
+#endif
+
 	/*
 	 * If the chosen entity does not match with the sched_data's
 	 * next_in_service and we are forcedly serving the IDLE priority
@@ -1045,10 +1244,28 @@ static struct bfq_entity *bfq_lookup_next_entity(struct bfq_sched_data *sd,
 	BUG_ON(sd->in_service_entity);
 
 	if (bfqd &&
-	    jiffies - bfqd->bfq_class_idle_last_service > BFQ_CL_IDLE_TIMEOUT) {
+	    jiffies - bfqd->bfq_class_idle_last_service >
+	    BFQ_CL_IDLE_TIMEOUT) {
 		entity = __bfq_lookup_next_entity(st + BFQ_IOPRIO_CLASSES - 1,
 						  true);
 		if (entity) {
+			struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
+			if (bfqq)
+				bfq_log_bfqq(bfqd, bfqq,
+					     "idle chosen from st %p %d",
+					     st + BFQ_IOPRIO_CLASSES - 1,
+					BFQ_IOPRIO_CLASSES - 1) ;
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+			else {
+				struct bfq_group *bfqg =
+				container_of(entity, struct bfq_group, entity);
+
+				bfq_log_bfqg(bfqd, bfqg,
+					     "idle chosen from st %p %d",
+					     st + BFQ_IOPRIO_CLASSES - 1,
+					BFQ_IOPRIO_CLASSES - 1) ;
+			}
+#endif
 			i = BFQ_IOPRIO_CLASSES - 1;
 			bfqd->bfq_class_idle_last_service = jiffies;
 			sd->next_in_service = entity;
@@ -1057,6 +1274,24 @@ static struct bfq_entity *bfq_lookup_next_entity(struct bfq_sched_data *sd,
 	for (; i < BFQ_IOPRIO_CLASSES; i++) {
 		entity = __bfq_lookup_next_entity(st + i, false);
 		if (entity) {
+			if (bfqd != NULL) {
+			struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
+			if (bfqq)
+				bfq_log_bfqq(bfqd, bfqq,
+					     "chosen from st %p %d",
+					     st + i, i) ;
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+			else {
+				struct bfq_group *bfqg =
+				container_of(entity, struct bfq_group, entity);
+
+				bfq_log_bfqg(bfqd, bfqg,
+					     "chosen from st %p %d",
+					     st + i, i) ;
+			}
+#endif
+			}
+
 			if (extract) {
 				bfq_check_next_in_service(sd, entity);
 				bfq_active_extract(st + i, entity);
@@ -1070,6 +1305,13 @@ static struct bfq_entity *bfq_lookup_next_entity(struct bfq_sched_data *sd,
 	return entity;
 }
 
+static bool next_queue_may_preempt(struct bfq_data *bfqd)
+{
+	struct bfq_sched_data *sd = &bfqd->root_group->sched_data;
+
+	return sd->next_in_service != sd->in_service_entity;
+}
+
 /*
  * Get next queue for service.
  */
@@ -1086,7 +1328,36 @@ static struct bfq_queue *bfq_get_next_queue(struct bfq_data *bfqd)
 
 	sd = &bfqd->root_group->sched_data;
 	for (; sd ; sd = entity->my_sched_data) {
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+		if (entity) {
+			struct bfq_group *bfqg =
+				container_of(entity, struct bfq_group, entity);
+
+			bfq_log_bfqg(bfqd, bfqg,
+				     "get_next_queue: lookup in this group");
+		} else
+			bfq_log_bfqg(bfqd, bfqd->root_group,
+				     "get_next_queue: lookup in root group");
+#endif
+
 		entity = bfq_lookup_next_entity(sd, 1, bfqd);
+
+		bfqq = bfq_entity_to_bfqq(entity);
+		if (bfqq)
+			bfq_log_bfqq(bfqd, bfqq,
+			     "get_next_queue: this queue, finish %llu",
+				(((entity->finish>>10)*1000)>>10)>>2);
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+		else {
+			struct bfq_group *bfqg =
+				container_of(entity, struct bfq_group, entity);
+
+			bfq_log_bfqg(bfqd, bfqg,
+			     "get_next_queue: this entity, finish %llu",
+				(((entity->finish>>10)*1000)>>10)>>2);
+		}
+#endif
+
 		BUG_ON(!entity);
 		entity->service = 0;
 	}
@@ -1113,9 +1384,7 @@ static void bfq_deactivate_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 {
 	struct bfq_entity *entity = &bfqq->entity;
 
-	if (bfqq == bfqd->in_service_queue)
-		__bfq_bfqd_reset_in_service(bfqd);
-
+	BUG_ON(bfqq == bfqd->in_service_queue);
 	bfq_deactivate_entity(entity, requeue);
 }
 
@@ -1123,12 +1392,11 @@ static void bfq_activate_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
 {
 	struct bfq_entity *entity = &bfqq->entity;
 
-	bfq_activate_entity(entity);
+	bfq_activate_entity(entity, bfq_bfqq_non_blocking_wait_rq(bfqq));
+	bfq_clear_bfqq_non_blocking_wait_rq(bfqq);
 }
 
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
 static void bfqg_stats_update_dequeue(struct bfq_group *bfqg);
-#endif
 
 /*
  * Called when the bfqq no longer has requests pending, remove it from
@@ -1139,6 +1407,7 @@ static void bfq_del_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 {
 	BUG_ON(!bfq_bfqq_busy(bfqq));
 	BUG_ON(!RB_EMPTY_ROOT(&bfqq->sort_list));
+	BUG_ON(bfqq == bfqd->in_service_queue);
 
 	bfq_log_bfqq(bfqd, bfqq, "del from busy");
 
@@ -1147,27 +1416,20 @@ static void bfq_del_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 	BUG_ON(bfqd->busy_queues == 0);
 	bfqd->busy_queues--;
 
-	if (!bfqq->dispatched) {
+	if (!bfqq->dispatched)
 		bfq_weights_tree_remove(bfqd, &bfqq->entity,
 					&bfqd->queue_weights_tree);
-		if (!blk_queue_nonrot(bfqd->queue)) {
-			BUG_ON(!bfqd->busy_in_flight_queues);
-			bfqd->busy_in_flight_queues--;
-			if (bfq_bfqq_constantly_seeky(bfqq)) {
-				BUG_ON(!bfqd->
-					const_seeky_busy_in_flight_queues);
-				bfqd->const_seeky_busy_in_flight_queues--;
-			}
-		}
-	}
+
 	if (bfqq->wr_coeff > 1)
 		bfqd->wr_busy_queues--;
 
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
 	bfqg_stats_update_dequeue(bfqq_group(bfqq));
-#endif
 
+	BUG_ON(bfqq->entity.budget < 0);
+	
 	bfq_deactivate_bfqq(bfqd, bfqq, requeue);
+
+	BUG_ON(bfqq->entity.budget < 0);
 }
 
 /*
@@ -1185,16 +1447,11 @@ static void bfq_add_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq)
 	bfq_mark_bfqq_busy(bfqq);
 	bfqd->busy_queues++;
 
-	if (!bfqq->dispatched) {
+	if (!bfqq->dispatched)
 		if (bfqq->wr_coeff == 1)
 			bfq_weights_tree_add(bfqd, &bfqq->entity,
 					     &bfqd->queue_weights_tree);
-		if (!blk_queue_nonrot(bfqd->queue)) {
-			bfqd->busy_in_flight_queues++;
-			if (bfq_bfqq_constantly_seeky(bfqq))
-				bfqd->const_seeky_busy_in_flight_queues++;
-		}
-	}
+
 	if (bfqq->wr_coeff > 1)
 		bfqd->wr_busy_queues++;
 }
diff --git a/block/bfq.h b/block/bfq.h
index f73c9427acc3..49d28b9dc9ca 100644
--- a/block/bfq.h
+++ b/block/bfq.h
@@ -1,5 +1,5 @@
 /*
- * BFQ-v7r11 for 4.5.0: data structures and common functions prototypes.
+ * BFQ-v8r3 for 4.7.0: data structures and common functions prototypes.
  *
  * Based on ideas and code from CFQ:
  * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
@@ -28,20 +28,21 @@
 
 #define BFQ_DEFAULT_QUEUE_IOPRIO	4
 
-#define BFQ_DEFAULT_GRP_WEIGHT	10
+#define BFQ_WEIGHT_LEGACY_DFL	100
 #define BFQ_DEFAULT_GRP_IOPRIO	0
 #define BFQ_DEFAULT_GRP_CLASS	IOPRIO_CLASS_BE
 
+/*
+ * Soft real-time applications are extremely more latency sensitive
+ * than interactive ones. Over-raise the weight of the former to
+ * privilege them against the latter.
+ */
+#define BFQ_SOFTRT_WEIGHT_FACTOR	100
+
 struct bfq_entity;
 
 /**
  * struct bfq_service_tree - per ioprio_class service tree.
- * @active: tree for active entities (i.e., those backlogged).
- * @idle: tree for idle entities (i.e., those not backlogged, with V <= F_i).
- * @first_idle: idle entity with minimum F_i.
- * @last_idle: idle entity with maximum F_i.
- * @vtime: scheduler virtual time.
- * @wsum: scheduler weight sum; active and idle entities contribute to it.
  *
  * Each service tree represents a B-WF2Q+ scheduler on its own.  Each
  * ioprio_class has its own independent scheduler, and so its own
@@ -49,27 +50,28 @@ struct bfq_entity;
  * of the containing bfqd.
  */
 struct bfq_service_tree {
+	/* tree for active entities (i.e., those backlogged) */
 	struct rb_root active;
+	/* tree for idle entities (i.e., not backlogged, with V <= F_i)*/
 	struct rb_root idle;
 
-	struct bfq_entity *first_idle;
-	struct bfq_entity *last_idle;
+	struct bfq_entity *first_idle; 	/* idle entity with minimum F_i */
+	struct bfq_entity *last_idle; 	/* idle entity with maximum F_i */
 
-	u64 vtime;
+	u64 vtime; /* scheduler virtual time */
+	/* scheduler weight sum; active and idle entities contribute to it */
 	unsigned long wsum;
 };
 
 /**
  * struct bfq_sched_data - multi-class scheduler.
- * @in_service_entity: entity in service.
- * @next_in_service: head-of-the-line entity in the scheduler.
- * @service_tree: array of service trees, one per ioprio_class.
  *
  * bfq_sched_data is the basic scheduler queue.  It supports three
- * ioprio_classes, and can be used either as a toplevel queue or as
- * an intermediate queue on a hierarchical setup.
- * @next_in_service points to the active entity of the sched_data
- * service trees that will be scheduled next.
+ * ioprio_classes, and can be used either as a toplevel queue or as an
+ * intermediate queue on a hierarchical setup.  @next_in_service
+ * points to the active entity of the sched_data service trees that
+ * will be scheduled next. It is used to reduce the number of steps
+ * needed for each hierarchical-schedule update.
  *
  * The supported ioprio_classes are the same as in CFQ, in descending
  * priority order, IOPRIO_CLASS_RT, IOPRIO_CLASS_BE, IOPRIO_CLASS_IDLE.
@@ -79,48 +81,29 @@ struct bfq_service_tree {
  * All the fields are protected by the queue lock of the containing bfqd.
  */
 struct bfq_sched_data {
-	struct bfq_entity *in_service_entity;
+	struct bfq_entity *in_service_entity;  /* entity in service */
+	/* head-of-the-line entity in the scheduler (see comments above) */
 	struct bfq_entity *next_in_service;
+	/* array of service trees, one per ioprio_class */
 	struct bfq_service_tree service_tree[BFQ_IOPRIO_CLASSES];
 };
 
 /**
  * struct bfq_weight_counter - counter of the number of all active entities
  *                             with a given weight.
- * @weight: weight of the entities that this counter refers to.
- * @num_active: number of active entities with this weight.
- * @weights_node: weights tree member (see bfq_data's @queue_weights_tree
- *                and @group_weights_tree).
  */
 struct bfq_weight_counter {
-	short int weight;
-	unsigned int num_active;
+	unsigned int weight; /* weight of the entities this counter refers to */
+	unsigned int num_active; /* nr of active entities with this weight */
+	/*
+	 * Weights tree member (see bfq_data's @queue_weights_tree and
+	 * @group_weights_tree)
+	 */
 	struct rb_node weights_node;
 };
 
 /**
  * struct bfq_entity - schedulable entity.
- * @rb_node: service_tree member.
- * @weight_counter: pointer to the weight counter associated with this entity.
- * @on_st: flag, true if the entity is on a tree (either the active or
- *         the idle one of its service_tree).
- * @finish: B-WF2Q+ finish timestamp (aka F_i).
- * @start: B-WF2Q+ start timestamp (aka S_i).
- * @tree: tree the entity is enqueued into; %NULL if not on a tree.
- * @min_start: minimum start time of the (active) subtree rooted at
- *             this entity; used for O(log N) lookups into active trees.
- * @service: service received during the last round of service.
- * @budget: budget used to calculate F_i; F_i = S_i + @budget / @weight.
- * @weight: weight of the queue
- * @parent: parent entity, for hierarchical scheduling.
- * @my_sched_data: for non-leaf nodes in the cgroup hierarchy, the
- *                 associated scheduler queue, %NULL on leaf nodes.
- * @sched_data: the scheduler queue this entity belongs to.
- * @ioprio: the ioprio in use.
- * @new_weight: when a weight change is requested, the new weight value.
- * @orig_weight: original weight, used to implement weight boosting
- * @prio_changed: flag, true when the user requested a weight, ioprio or
- *		  ioprio_class change.
  *
  * A bfq_entity is used to represent either a bfq_queue (leaf node in the
  * cgroup hierarchy) or a bfq_group into the upper level scheduler.  Each
@@ -147,27 +130,52 @@ struct bfq_weight_counter {
  * containing bfqd.
  */
 struct bfq_entity {
-	struct rb_node rb_node;
+	struct rb_node rb_node; /* service_tree member */
+	/* pointer to the weight counter associated with this entity */
 	struct bfq_weight_counter *weight_counter;
 
+	/*
+	 * flag, true if the entity is on a tree (either the active or
+	 * the idle one of its service_tree).
+	 */
 	int on_st;
 
-	u64 finish;
-	u64 start;
+	u64 finish; /* B-WF2Q+ finish timestamp (aka F_i) */
+	u64 start;  /* B-WF2Q+ start timestamp (aka S_i) */
 
+	/* tree the entity is enqueued into; %NULL if not on a tree */
 	struct rb_root *tree;
 
+	/*
+	 * minimum start time of the (active) subtree rooted at this
+	 * entity; used for O(log N) lookups into active trees
+	 */
 	u64 min_start;
 
-	int service, budget;
-	unsigned short weight, new_weight;
-	unsigned short orig_weight;
+	/* amount of service received during the last service slot */
+	int service;
 
+	/* budget, used also to calculate F_i: F_i = S_i + @budget / @weight */
+	int budget;
+
+	unsigned int weight; 	/* weight of the queue */
+	unsigned int new_weight; /* next weight if a change is in progress */
+
+	/* original weight, used to implement weight boosting */
+	unsigned int orig_weight;
+
+	/* parent entity, for hierarchical scheduling */
 	struct bfq_entity *parent;
 
+	/*
+	 * For non-leaf nodes in the hierarchy, the associated
+	 * scheduler queue, %NULL on leaf nodes.
+	 */
 	struct bfq_sched_data *my_sched_data;
+	/* the scheduler queue this entity belongs to */
 	struct bfq_sched_data *sched_data;
 
+	/* flag, set to request a weight, ioprio or ioprio_class change  */
 	int prio_changed;
 };
 
@@ -175,56 +183,6 @@ struct bfq_group;
 
 /**
  * struct bfq_queue - leaf schedulable entity.
- * @ref: reference counter.
- * @bfqd: parent bfq_data.
- * @new_ioprio: when an ioprio change is requested, the new ioprio value.
- * @ioprio_class: the ioprio_class in use.
- * @new_ioprio_class: when an ioprio_class change is requested, the new
- *                    ioprio_class value.
- * @new_bfqq: shared bfq_queue if queue is cooperating with
- *           one or more other queues.
- * @pos_node: request-position tree member (see bfq_group's @rq_pos_tree).
- * @pos_root: request-position tree root (see bfq_group's @rq_pos_tree).
- * @sort_list: sorted list of pending requests.
- * @next_rq: if fifo isn't expired, next request to serve.
- * @queued: nr of requests queued in @sort_list.
- * @allocated: currently allocated requests.
- * @meta_pending: pending metadata requests.
- * @fifo: fifo list of requests in sort_list.
- * @entity: entity representing this queue in the scheduler.
- * @max_budget: maximum budget allowed from the feedback mechanism.
- * @budget_timeout: budget expiration (in jiffies).
- * @dispatched: number of requests on the dispatch list or inside driver.
- * @flags: status flags.
- * @bfqq_list: node for active/idle bfqq list inside our bfqd.
- * @burst_list_node: node for the device's burst list.
- * @seek_samples: number of seeks sampled
- * @seek_total: sum of the distances of the seeks sampled
- * @seek_mean: mean seek distance
- * @last_request_pos: position of the last request enqueued
- * @requests_within_timer: number of consecutive pairs of request completion
- *                         and arrival, such that the queue becomes idle
- *                         after the completion, but the next request arrives
- *                         within an idle time slice; used only if the queue's
- *                         IO_bound has been cleared.
- * @pid: pid of the process owning the queue, used for logging purposes.
- * @last_wr_start_finish: start time of the current weight-raising period if
- *                        the @bfq-queue is being weight-raised, otherwise
- *                        finish time of the last weight-raising period
- * @wr_cur_max_time: current max raising time for this queue
- * @soft_rt_next_start: minimum time instant such that, only if a new
- *                      request is enqueued after this time instant in an
- *                      idle @bfq_queue with no outstanding requests, then
- *                      the task associated with the queue it is deemed as
- *                      soft real-time (see the comments to the function
- *                      bfq_bfqq_softrt_next_start())
- * @last_idle_bklogged: time of the last transition of the @bfq_queue from
- *                      idle to backlogged
- * @service_from_backlogged: cumulative service received from the @bfq_queue
- *                           since the last transition from idle to
- *                           backlogged
- * @bic: pointer to the bfq_io_cq owning the bfq_queue, set to %NULL if the
- *	 queue is shared
  *
  * A bfq_queue is a leaf request queue; it can be associated with an
  * io_context or more, if it  is  async or shared  between  cooperating
@@ -235,117 +193,163 @@ struct bfq_group;
  * All the fields are protected by the queue lock of the containing bfqd.
  */
 struct bfq_queue {
-	atomic_t ref;
+	/* reference counter */
+	int ref;
+	/* parent bfq_data */
 	struct bfq_data *bfqd;
 
-	unsigned short ioprio, new_ioprio;
-	unsigned short ioprio_class, new_ioprio_class;
+	/* current ioprio and ioprio class */
+	unsigned short ioprio, ioprio_class;
+	/* next ioprio and ioprio class if a change is in progress */
+	unsigned short new_ioprio, new_ioprio_class;
 
-	/* fields for cooperating queues handling */
+	/*
+	 * Shared bfq_queue if queue is cooperating with one or more
+	 * other queues.
+	 */
 	struct bfq_queue *new_bfqq;
+	/* request-position tree member (see bfq_group's @rq_pos_tree) */
 	struct rb_node pos_node;
+	/* request-position tree root (see bfq_group's @rq_pos_tree) */
 	struct rb_root *pos_root;
 
+	/* sorted list of pending requests */
 	struct rb_root sort_list;
+	/* if fifo isn't expired, next request to serve */
 	struct request *next_rq;
+	/* number of sync and async requests queued */
 	int queued[2];
+	/* number of sync and async requests currently allocated */
 	int allocated[2];
+	/* number of pending metadata requests */
 	int meta_pending;
+	/* fifo list of requests in sort_list */
 	struct list_head fifo;
 
+	/* entity representing this queue in the scheduler */
 	struct bfq_entity entity;
 
+	/* maximum budget allowed from the feedback mechanism */
 	int max_budget;
+	/* budget expiration (in jiffies) */
 	unsigned long budget_timeout;
 
+	/* number of requests on the dispatch list or inside driver */
 	int dispatched;
 
-	unsigned int flags;
+	unsigned int flags; /* status flags.*/
 
+	/* node for active/idle bfqq list inside parent bfqd */
 	struct list_head bfqq_list;
 
+	/* bit vector: a 1 for each seeky requests in history */
+	u32 seek_history;
+
+	/* node for the device's burst list */
 	struct hlist_node burst_list_node;
 
-	unsigned int seek_samples;
-	u64 seek_total;
-	sector_t seek_mean;
+	/* position of the last request enqueued */
 	sector_t last_request_pos;
 
+	/* Number of consecutive pairs of request completion and
+	 * arrival, such that the queue becomes idle after the
+	 * completion, but the next request arrives within an idle
+	 * time slice; used only if the queue's IO_bound flag has been
+	 * cleared.
+	 */
 	unsigned int requests_within_timer;
 
+	/* pid of the process owning the queue, used for logging purposes */
 	pid_t pid;
+
+	/*
+	 * Pointer to the bfq_io_cq owning the bfq_queue, set to %NULL
+	 * if the queue is shared.
+	 */
 	struct bfq_io_cq *bic;
 
-	/* weight-raising fields */
+	/* current maximum weight-raising time for this queue */
 	unsigned long wr_cur_max_time;
+	/*
+	 * Minimum time instant such that, only if a new request is
+	 * enqueued after this time instant in an idle @bfq_queue with
+	 * no outstanding requests, then the task associated with the
+	 * queue it is deemed as soft real-time (see the comments on
+	 * the function bfq_bfqq_softrt_next_start())
+	 */
 	unsigned long soft_rt_next_start;
+	/*
+	 * Start time of the current weight-raising period if
+	 * the @bfq-queue is being weight-raised, otherwise
+	 * finish time of the last weight-raising period.
+	 */
 	unsigned long last_wr_start_finish;
+	/* factor by which the weight of this queue is multiplied */
 	unsigned int wr_coeff;
+	/*
+	 * Time of the last transition of the @bfq_queue from idle to
+	 * backlogged.
+	 */
 	unsigned long last_idle_bklogged;
+	/*
+	 * Cumulative service received from the @bfq_queue since the
+	 * last transition from idle to backlogged.
+	 */
 	unsigned long service_from_backlogged;
+
+	unsigned long split_time; /* time of last split */
 };
 
 /**
  * struct bfq_ttime - per process thinktime stats.
- * @ttime_total: total process thinktime
- * @ttime_samples: number of thinktime samples
- * @ttime_mean: average process thinktime
  */
 struct bfq_ttime {
-	unsigned long last_end_request;
+	unsigned long last_end_request; /* completion time of last request */
+
+	unsigned long ttime_total; /* total process thinktime */
+	unsigned long ttime_samples; /* number of thinktime samples */
+	unsigned long ttime_mean; /* average process thinktime */
 
-	unsigned long ttime_total;
-	unsigned long ttime_samples;
-	unsigned long ttime_mean;
 };
 
 /**
  * struct bfq_io_cq - per (request_queue, io_context) structure.
- * @icq: associated io_cq structure
- * @bfqq: array of two process queues, the sync and the async
- * @ttime: associated @bfq_ttime struct
- * @ioprio: per (request_queue, blkcg) ioprio.
- * @blkcg_id: id of the blkcg the related io_cq belongs to.
- * @wr_time_left: snapshot of the time left before weight raising ends
- *                for the sync queue associated to this process; this
- *		  snapshot is taken to remember this value while the weight
- *		  raising is suspended because the queue is merged with a
- *		  shared queue, and is used to set @raising_cur_max_time
- *		  when the queue is split from the shared queue and its
- *		  weight is raised again
- * @saved_idle_window: same purpose as the previous field for the idle
- *                     window
- * @saved_IO_bound: same purpose as the previous two fields for the I/O
- *                  bound classification of a queue
- * @saved_in_large_burst: same purpose as the previous fields for the
- *                        value of the field keeping the queue's belonging
- *                        to a large burst
- * @was_in_burst_list: true if the queue belonged to a burst list
- *                     before its merge with another cooperating queue
- * @cooperations: counter of consecutive successful queue merges underwent
- *                by any of the process' @bfq_queues
- * @failed_cooperations: counter of consecutive failed queue merges of any
- *                       of the process' @bfq_queues
  */
 struct bfq_io_cq {
+	/* associated io_cq structure */
 	struct io_cq icq; /* must be the first member */
+	/* array of two process queues, the sync and the async */
 	struct bfq_queue *bfqq[2];
+	/* associated @bfq_ttime struct */
 	struct bfq_ttime ttime;
+	/* per (request_queue, blkcg) ioprio */
 	int ioprio;
-
 #ifdef CONFIG_BFQ_GROUP_IOSCHED
-	uint64_t blkcg_id; /* the current blkcg ID */
+	uint64_t blkcg_serial_nr; /* the current blkcg serial */
 #endif
 
-	unsigned int wr_time_left;
+	/*
+	 * Snapshot of the idle window before merging; taken to
+	 * remember this value while the queue is merged, so as to be
+	 * able to restore it in case of split.
+	 */
 	bool saved_idle_window;
+	/*
+	 * Same purpose as the previous two fields for the I/O bound
+	 * classification of a queue.
+	 */
 	bool saved_IO_bound;
 
+	/*
+	 * Same purpose as the previous fields for the value of the
+	 * field keeping the queue's belonging to a large burst
+	 */
 	bool saved_in_large_burst;
+	/*
+	 * True if the queue belonged to a burst list before its merge
+	 * with another cooperating queue.
+	 */
 	bool was_in_burst_list;
-
-	unsigned int cooperations;
-	unsigned int failed_cooperations;
 };
 
 enum bfq_device_speed {
@@ -354,224 +358,216 @@ enum bfq_device_speed {
 };
 
 /**
- * struct bfq_data - per device data structure.
- * @queue: request queue for the managed device.
- * @root_group: root bfq_group for the device.
- * @active_numerous_groups: number of bfq_groups containing more than one
- *                          active @bfq_entity.
- * @queue_weights_tree: rbtree of weight counters of @bfq_queues, sorted by
- *                      weight. Used to keep track of whether all @bfq_queues
- *                     have the same weight. The tree contains one counter
- *                     for each distinct weight associated to some active
- *                     and not weight-raised @bfq_queue (see the comments to
- *                      the functions bfq_weights_tree_[add|remove] for
- *                     further details).
- * @group_weights_tree: rbtree of non-queue @bfq_entity weight counters, sorted
- *                      by weight. Used to keep track of whether all
- *                     @bfq_groups have the same weight. The tree contains
- *                     one counter for each distinct weight associated to
- *                     some active @bfq_group (see the comments to the
- *                     functions bfq_weights_tree_[add|remove] for further
- *                     details).
- * @busy_queues: number of bfq_queues containing requests (including the
- *		 queue in service, even if it is idling).
- * @busy_in_flight_queues: number of @bfq_queues containing pending or
- *                         in-flight requests, plus the @bfq_queue in
- *                         service, even if idle but waiting for the
- *                         possible arrival of its next sync request. This
- *                         field is updated only if the device is rotational,
- *                         but used only if the device is also NCQ-capable.
- *                         The reason why the field is updated also for non-
- *                         NCQ-capable rotational devices is related to the
- *                         fact that the value of @hw_tag may be set also
- *                         later than when busy_in_flight_queues may need to
- *                         be incremented for the first time(s). Taking also
- *                         this possibility into account, to avoid unbalanced
- *                         increments/decrements, would imply more overhead
- *                         than just updating busy_in_flight_queues
- *                         regardless of the value of @hw_tag.
- * @const_seeky_busy_in_flight_queues: number of constantly-seeky @bfq_queues
- *                                     (that is, seeky queues that expired
- *                                     for budget timeout at least once)
- *                                     containing pending or in-flight
- *                                     requests, including the in-service
- *                                     @bfq_queue if constantly seeky. This
- *                                     field is updated only if the device
- *                                     is rotational, but used only if the
- *                                     device is also NCQ-capable (see the
- *                                     comments to @busy_in_flight_queues).
- * @wr_busy_queues: number of weight-raised busy @bfq_queues.
- * @queued: number of queued requests.
- * @rq_in_driver: number of requests dispatched and waiting for completion.
- * @sync_flight: number of sync requests in the driver.
- * @max_rq_in_driver: max number of reqs in driver in the last
- *                    @hw_tag_samples completed requests.
- * @hw_tag_samples: nr of samples used to calculate hw_tag.
- * @hw_tag: flag set to one if the driver is showing a queueing behavior.
- * @budgets_assigned: number of budgets assigned.
- * @idle_slice_timer: timer set when idling for the next sequential request
- *                    from the queue in service.
- * @unplug_work: delayed work to restart dispatching on the request queue.
- * @in_service_queue: bfq_queue in service.
- * @in_service_bic: bfq_io_cq (bic) associated with the @in_service_queue.
- * @last_position: on-disk position of the last served request.
- * @last_budget_start: beginning of the last budget.
- * @last_idling_start: beginning of the last idle slice.
- * @peak_rate: peak transfer rate observed for a budget.
- * @peak_rate_samples: number of samples used to calculate @peak_rate.
- * @bfq_max_budget: maximum budget allotted to a bfq_queue before
- *                  rescheduling.
- * @active_list: list of all the bfq_queues active on the device.
- * @idle_list: list of all the bfq_queues idle on the device.
- * @bfq_fifo_expire: timeout for async/sync requests; when it expires
- *                   requests are served in fifo order.
- * @bfq_back_penalty: weight of backward seeks wrt forward ones.
- * @bfq_back_max: maximum allowed backward seek.
- * @bfq_slice_idle: maximum idling time.
- * @bfq_user_max_budget: user-configured max budget value
- *                       (0 for auto-tuning).
- * @bfq_max_budget_async_rq: maximum budget (in nr of requests) allotted to
- *                           async queues.
- * @bfq_timeout: timeout for bfq_queues to consume their budget; used to
- *               to prevent seeky queues to impose long latencies to well
- *               behaved ones (this also implies that seeky queues cannot
- *               receive guarantees in the service domain; after a timeout
- *               they are charged for the whole allocated budget, to try
- *               to preserve a behavior reasonably fair among them, but
- *               without service-domain guarantees).
- * @bfq_coop_thresh: number of queue merges after which a @bfq_queue is
- *                   no more granted any weight-raising.
- * @bfq_failed_cooperations: number of consecutive failed cooperation
- *                           chances after which weight-raising is restored
- *                           to a queue subject to more than bfq_coop_thresh
- *                           queue merges.
- * @bfq_requests_within_timer: number of consecutive requests that must be
- *                             issued within the idle time slice to set
- *                             again idling to a queue which was marked as
- *                             non-I/O-bound (see the definition of the
- *                             IO_bound flag for further details).
- * @last_ins_in_burst: last time at which a queue entered the current
- *                     burst of queues being activated shortly after
- *                     each other; for more details about this and the
- *                     following parameters related to a burst of
- *                     activations, see the comments to the function
- *                     @bfq_handle_burst.
- * @bfq_burst_interval: reference time interval used to decide whether a
- *                      queue has been activated shortly after
- *                      @last_ins_in_burst.
- * @burst_size: number of queues in the current burst of queue activations.
- * @bfq_large_burst_thresh: maximum burst size above which the current
- * 			    queue-activation burst is deemed as 'large'.
- * @large_burst: true if a large queue-activation burst is in progress.
- * @burst_list: head of the burst list (as for the above fields, more details
- * 		in the comments to the function bfq_handle_burst).
- * @low_latency: if set to true, low-latency heuristics are enabled.
- * @bfq_wr_coeff: maximum factor by which the weight of a weight-raised
- *                queue is multiplied.
- * @bfq_wr_max_time: maximum duration of a weight-raising period (jiffies).
- * @bfq_wr_rt_max_time: maximum duration for soft real-time processes.
- * @bfq_wr_min_idle_time: minimum idle period after which weight-raising
- *			  may be reactivated for a queue (in jiffies).
- * @bfq_wr_min_inter_arr_async: minimum period between request arrivals
- *				after which weight-raising may be
- *				reactivated for an already busy queue
- *				(in jiffies).
- * @bfq_wr_max_softrt_rate: max service-rate for a soft real-time queue,
- *			    sectors per seconds.
- * @RT_prod: cached value of the product R*T used for computing the maximum
- *	     duration of the weight raising automatically.
- * @device_speed: device-speed class for the low-latency heuristic.
- * @oom_bfqq: fallback dummy bfqq for extreme OOM conditions.
+ * struct bfq_data - per-device data structure.
  *
  * All the fields are protected by the @queue lock.
  */
 struct bfq_data {
+	/* request queue for the device */
 	struct request_queue *queue;
 
+	/* root bfq_group for the device */
 	struct bfq_group *root_group;
 
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
-	int active_numerous_groups;
-#endif
-
+	/*
+	 * rbtree of weight counters of @bfq_queues, sorted by
+	 * weight. Used to keep track of whether all @bfq_queues have
+	 * the same weight. The tree contains one counter for each
+	 * distinct weight associated to some active and not
+	 * weight-raised @bfq_queue (see the comments to the functions
+	 * bfq_weights_tree_[add|remove] for further details).
+	 */
 	struct rb_root queue_weights_tree;
+	/*
+	 * rbtree of non-queue @bfq_entity weight counters, sorted by
+	 * weight. Used to keep track of whether all @bfq_groups have
+	 * the same weight. The tree contains one counter for each
+	 * distinct weight associated to some active @bfq_group (see
+	 * the comments to the functions bfq_weights_tree_[add|remove]
+	 * for further details).
+	 */
 	struct rb_root group_weights_tree;
 
+	/*
+	 * Number of bfq_queues containing requests (including the
+	 * queue in service, even if it is idling).
+	 */
 	int busy_queues;
-	int busy_in_flight_queues;
-	int const_seeky_busy_in_flight_queues;
+	/* number of weight-raised busy @bfq_queues */
 	int wr_busy_queues;
+	/* number of queued requests */
 	int queued;
+	/* number of requests dispatched and waiting for completion */
 	int rq_in_driver;
-	int sync_flight;
 
+	/*
+	 * Maximum number of requests in driver in the last
+	 * @hw_tag_samples completed requests.
+	 */
 	int max_rq_in_driver;
+	/* number of samples used to calculate hw_tag */
 	int hw_tag_samples;
+	/* flag set to one if the driver is showing a queueing behavior */
 	int hw_tag;
 
+	/* number of budgets assigned */
 	int budgets_assigned;
 
+	/*
+	 * Timer set when idling (waiting) for the next request from
+	 * the queue in service.
+	 */
 	struct timer_list idle_slice_timer;
+	/* delayed work to restart dispatching on the request queue */
 	struct work_struct unplug_work;
 
+	/* bfq_queue in service */
 	struct bfq_queue *in_service_queue;
+	/* bfq_io_cq (bic) associated with the @in_service_queue */
 	struct bfq_io_cq *in_service_bic;
 
+	/* on-disk position of the last served request */
 	sector_t last_position;
 
+	/* beginning of the last budget */
 	ktime_t last_budget_start;
+	/* beginning of the last idle slice */
 	ktime_t last_idling_start;
+	/* number of samples used to calculate @peak_rate */
 	int peak_rate_samples;
+	/* peak transfer rate observed for a budget */
 	u64 peak_rate;
+	/* maximum budget allotted to a bfq_queue before rescheduling */
 	int bfq_max_budget;
 
+	/* list of all the bfq_queues active on the device */
 	struct list_head active_list;
+	/* list of all the bfq_queues idle on the device */
 	struct list_head idle_list;
 
+	/*
+	 * Timeout for async/sync requests; when it fires, requests
+	 * are served in fifo order.
+	 */
 	unsigned int bfq_fifo_expire[2];
+	/* weight of backward seeks wrt forward ones */
 	unsigned int bfq_back_penalty;
+	/* maximum allowed backward seek */
 	unsigned int bfq_back_max;
+	/* maximum idling time */
 	unsigned int bfq_slice_idle;
+	/* last time CLASS_IDLE was served */
 	u64 bfq_class_idle_last_service;
 
+	/* user-configured max budget value (0 for auto-tuning) */
 	int bfq_user_max_budget;
-	int bfq_max_budget_async_rq;
-	unsigned int bfq_timeout[2];
+	/*
+	 * Timeout for bfq_queues to consume their budget; used to
+	 * prevent seeky queues from imposing long latencies to
+	 * sequential or quasi-sequential ones (this also implies that
+	 * seeky queues cannot receive guarantees in the service
+	 * domain; after a timeout they are charged for the time they
+	 * have been in service, to preserve fairness among them, but
+	 * without service-domain guarantees).
+	 */
+	unsigned int bfq_timeout;
 
-	unsigned int bfq_coop_thresh;
-	unsigned int bfq_failed_cooperations;
+	/*
+	 * Number of consecutive requests that must be issued within
+	 * the idle time slice to set again idling to a queue which
+	 * was marked as non-I/O-bound (see the definition of the
+	 * IO_bound flag for further details).
+	 */
 	unsigned int bfq_requests_within_timer;
 
+	/*
+	 * Force device idling whenever needed to provide accurate
+	 * service guarantees, without caring about throughput
+	 * issues. CAVEAT: this may even increase latencies, in case
+	 * of useless idling for processes that did stop doing I/O.
+	 */
+	bool strict_guarantees;
+
+	/*
+	 * Last time at which a queue entered the current burst of
+	 * queues being activated shortly after each other; for more
+	 * details about this and the following parameters related to
+	 * a burst of activations, see the comments on the function
+	 * bfq_handle_burst.
+	 */
 	unsigned long last_ins_in_burst;
+	/*
+	 * Reference time interval used to decide whether a queue has
+	 * been activated shortly after @last_ins_in_burst.
+	 */
 	unsigned long bfq_burst_interval;
+	/* number of queues in the current burst of queue activations */
 	int burst_size;
+
+	/* common parent entity for the queues in the burst */
+	struct bfq_entity *burst_parent_entity;
+	/* Maximum burst size above which the current queue-activation
+	 * burst is deemed as 'large'.
+	 */
 	unsigned long bfq_large_burst_thresh;
+	/* true if a large queue-activation burst is in progress */
 	bool large_burst;
+	/*
+	 * Head of the burst list (as for the above fields, more
+	 * details in the comments on the function bfq_handle_burst).
+	 */
 	struct hlist_head burst_list;
 
+	/* if set to true, low-latency heuristics are enabled */
 	bool low_latency;
-
-	/* parameters of the low_latency heuristics */
+	/*
+	 * Maximum factor by which the weight of a weight-raised queue
+	 * is multiplied.
+	 */
 	unsigned int bfq_wr_coeff;
+	/* maximum duration of a weight-raising period (jiffies) */
 	unsigned int bfq_wr_max_time;
+
+	/* Maximum weight-raising duration for soft real-time processes */
 	unsigned int bfq_wr_rt_max_time;
+	/*
+	 * Minimum idle period after which weight-raising may be
+	 * reactivated for a queue (in jiffies).
+	 */
 	unsigned int bfq_wr_min_idle_time;
+	/*
+	 * Minimum period between request arrivals after which
+	 * weight-raising may be reactivated for an already busy async
+	 * queue (in jiffies).
+	 */
 	unsigned long bfq_wr_min_inter_arr_async;
+
+	/* Max service-rate for a soft real-time queue, in sectors/sec */
 	unsigned int bfq_wr_max_softrt_rate;
+	/*
+	 * Cached value of the product R*T, used for computing the
+	 * maximum duration of weight raising automatically.
+	 */
 	u64 RT_prod;
+	/* device-speed class for the low-latency heuristic */
 	enum bfq_device_speed device_speed;
 
+	/* fallback dummy bfqq for extreme OOM conditions */
 	struct bfq_queue oom_bfqq;
 };
 
 enum bfqq_state_flags {
-	BFQ_BFQQ_FLAG_busy = 0,		/* has requests or is in service */
+	BFQ_BFQQ_FLAG_just_created = 0,	/* queue just allocated */
+	BFQ_BFQQ_FLAG_busy,		/* has requests or is in service */
 	BFQ_BFQQ_FLAG_wait_request,	/* waiting for a request */
+	BFQ_BFQQ_FLAG_non_blocking_wait_rq, /*
+					     * waiting for a request
+					     * without idling the device
+					     */
 	BFQ_BFQQ_FLAG_must_alloc,	/* must be allowed rq alloc */
 	BFQ_BFQQ_FLAG_fifo_expire,	/* FIFO checked in this slice */
 	BFQ_BFQQ_FLAG_idle_window,	/* slice idling enabled */
 	BFQ_BFQQ_FLAG_sync,		/* synchronous queue */
-	BFQ_BFQQ_FLAG_budget_new,	/* no completion with this budget */
 	BFQ_BFQQ_FLAG_IO_bound,		/*
 					 * bfqq has timed-out at least once
 					 * having consumed at most 2/10 of
@@ -581,17 +577,12 @@ enum bfqq_state_flags {
 					 * bfqq activated in a large burst,
 					 * see comments to bfq_handle_burst.
 					 */
-	BFQ_BFQQ_FLAG_constantly_seeky,	/*
-					 * bfqq has proved to be slow and
-					 * seeky until budget timeout
-					 */
 	BFQ_BFQQ_FLAG_softrt_update,	/*
 					 * may need softrt-next-start
 					 * update
 					 */
 	BFQ_BFQQ_FLAG_coop,		/* bfqq is shared */
-	BFQ_BFQQ_FLAG_split_coop,	/* shared bfqq will be split */
-	BFQ_BFQQ_FLAG_just_split,	/* queue has just been split */
+	BFQ_BFQQ_FLAG_split_coop	/* shared bfqq will be split */
 };
 
 #define BFQ_BFQQ_FNS(name)						\
@@ -608,25 +599,53 @@ static int bfq_bfqq_##name(const struct bfq_queue *bfqq)		\
 	return ((bfqq)->flags & (1 << BFQ_BFQQ_FLAG_##name)) != 0;	\
 }
 
+BFQ_BFQQ_FNS(just_created);
 BFQ_BFQQ_FNS(busy);
 BFQ_BFQQ_FNS(wait_request);
+BFQ_BFQQ_FNS(non_blocking_wait_rq);
 BFQ_BFQQ_FNS(must_alloc);
 BFQ_BFQQ_FNS(fifo_expire);
 BFQ_BFQQ_FNS(idle_window);
 BFQ_BFQQ_FNS(sync);
-BFQ_BFQQ_FNS(budget_new);
 BFQ_BFQQ_FNS(IO_bound);
 BFQ_BFQQ_FNS(in_large_burst);
-BFQ_BFQQ_FNS(constantly_seeky);
 BFQ_BFQQ_FNS(coop);
 BFQ_BFQQ_FNS(split_coop);
-BFQ_BFQQ_FNS(just_split);
 BFQ_BFQQ_FNS(softrt_update);
 #undef BFQ_BFQQ_FNS
 
 /* Logging facilities. */
-#define bfq_log_bfqq(bfqd, bfqq, fmt, args...) \
-	blk_add_trace_msg((bfqd)->queue, "bfq%d " fmt, (bfqq)->pid, ##args)
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+static struct bfq_group *bfqq_group(struct bfq_queue *bfqq);
+static struct blkcg_gq *bfqg_to_blkg(struct bfq_group *bfqg);
+
+#define bfq_log_bfqq(bfqd, bfqq, fmt, args...)	do {			\
+	char __pbuf[128];						\
+									\
+	assert_spin_locked((bfqd)->queue->queue_lock);			\
+	blkg_path(bfqg_to_blkg(bfqq_group(bfqq)), __pbuf, sizeof(__pbuf)); \
+	blk_add_trace_msg((bfqd)->queue, "bfq%d%c %s " fmt, \
+			  (bfqq)->pid,			  \
+			  bfq_bfqq_sync((bfqq)) ? 'S' : 'A',	\
+			  __pbuf, ##args);				\
+} while (0)
+
+#define bfq_log_bfqg(bfqd, bfqg, fmt, args...)	do {			\
+	char __pbuf[128];						\
+									\
+	blkg_path(bfqg_to_blkg(bfqg), __pbuf, sizeof(__pbuf));		\
+	blk_add_trace_msg((bfqd)->queue, "%s " fmt, __pbuf, ##args);	\
+} while (0)
+
+#else /* CONFIG_BFQ_GROUP_IOSCHED */
+
+#define bfq_log_bfqq(bfqd, bfqq, fmt, args...)	\
+	blk_add_trace_msg((bfqd)->queue, "bfq%d%c " fmt, (bfqq)->pid,	\
+			bfq_bfqq_sync((bfqq)) ? 'S' : 'A',		\
+				##args)
+#define bfq_log_bfqg(bfqd, bfqg, fmt, args...)		do {} while (0)
+
+#endif /* CONFIG_BFQ_GROUP_IOSCHED */
 
 #define bfq_log(bfqd, fmt, args...) \
 	blk_add_trace_msg((bfqd)->queue, "bfq " fmt, ##args)
@@ -640,15 +659,12 @@ enum bfqq_expiration {
 	BFQ_BFQQ_BUDGET_TIMEOUT,	/* budget took too long to be used */
 	BFQ_BFQQ_BUDGET_EXHAUSTED,	/* budget consumed */
 	BFQ_BFQQ_NO_MORE_REQUESTS,	/* the queue has no more requests */
+	BFQ_BFQQ_PREEMPTED		/* preemption in progress */
 };
 
-#ifdef CONFIG_BFQ_GROUP_IOSCHED
 
 struct bfqg_stats {
-	/* total bytes transferred */
-	struct blkg_rwstat		service_bytes;
-	/* total IOs serviced, post merge */
-	struct blkg_rwstat		serviced;
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
 	/* number of ios merged */
 	struct blkg_rwstat		merged;
 	/* total time spent on device in ns, may not be accurate w/ queueing */
@@ -657,12 +673,8 @@ struct bfqg_stats {
 	struct blkg_rwstat		wait_time;
 	/* number of IOs queued up */
 	struct blkg_rwstat		queued;
-	/* total sectors transferred */
-	struct blkg_stat		sectors;
 	/* total disk time and nr sectors dispatched by this group */
 	struct blkg_stat		time;
-	/* time not charged to this cgroup */
-	struct blkg_stat		unaccounted_time;
 	/* sum of number of ios queued across all samples */
 	struct blkg_stat		avg_queue_size_sum;
 	/* count of samples taken for average */
@@ -680,8 +692,10 @@ struct bfqg_stats {
 	uint64_t			start_idle_time;
 	uint64_t			start_empty_time;
 	uint16_t			flags;
+#endif
 };
 
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
 /*
  * struct bfq_group_data - per-blkcg storage for the blkio subsystem.
  *
@@ -692,7 +706,7 @@ struct bfq_group_data {
 	/* must be the first member */
 	struct blkcg_policy_data pd;
 
-	unsigned short weight;
+	unsigned int weight;
 };
 
 /**
@@ -712,7 +726,7 @@ struct bfq_group_data {
  *                   unused for the root group. Used to know whether there
  *                   are groups with more than one active @bfq_entity
  *                   (see the comments to the function
- *                   bfq_bfqq_must_not_expire()).
+ *                   bfq_bfqq_may_idle()).
  * @rq_pos_tree: rbtree sorted by next_request position, used when
  *               determining if two or more queues have interleaving
  *               requests (see bfq_find_close_cooperator()).
@@ -745,7 +759,6 @@ struct bfq_group {
 	struct rb_root rq_pos_tree;
 
 	struct bfqg_stats stats;
-	struct bfqg_stats dead_stats;	/* stats pushed from dead children */
 };
 
 #else
@@ -767,11 +780,25 @@ bfq_entity_service_tree(struct bfq_entity *entity)
 	struct bfq_sched_data *sched_data = entity->sched_data;
 	struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
 	unsigned int idx = bfqq ? bfqq->ioprio_class - 1 :
-				  BFQ_DEFAULT_GRP_CLASS;
+				  BFQ_DEFAULT_GRP_CLASS - 1;
 
 	BUG_ON(idx >= BFQ_IOPRIO_CLASSES);
 	BUG_ON(sched_data == NULL);
 
+	if (bfqq)
+		bfq_log_bfqq(bfqq->bfqd, bfqq,
+			     "entity_service_tree %p %d",
+			     sched_data->service_tree + idx, idx) ;
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+	else {
+		struct bfq_group *bfqg =
+			container_of(entity, struct bfq_group, entity);
+
+		bfq_log_bfqg((struct bfq_data *)bfqg->bfqd, bfqg,
+			     "entity_service_tree %p %d",
+			     sched_data->service_tree + idx, idx) ;
+	}
+#endif
 	return sched_data->service_tree + idx;
 }
 
@@ -791,47 +818,6 @@ static struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic)
 	return bic->icq.q->elevator->elevator_data;
 }
 
-/**
- * bfq_get_bfqd_locked - get a lock to a bfqd using a RCU protected pointer.
- * @ptr: a pointer to a bfqd.
- * @flags: storage for the flags to be saved.
- *
- * This function allows bfqg->bfqd to be protected by the
- * queue lock of the bfqd they reference; the pointer is dereferenced
- * under RCU, so the storage for bfqd is assured to be safe as long
- * as the RCU read side critical section does not end.  After the
- * bfqd->queue->queue_lock is taken the pointer is rechecked, to be
- * sure that no other writer accessed it.  If we raced with a writer,
- * the function returns NULL, with the queue unlocked, otherwise it
- * returns the dereferenced pointer, with the queue locked.
- */
-static struct bfq_data *bfq_get_bfqd_locked(void **ptr, unsigned long *flags)
-{
-	struct bfq_data *bfqd;
-
-	rcu_read_lock();
-	bfqd = rcu_dereference(*(struct bfq_data **)ptr);
-
-	if (bfqd != NULL) {
-		spin_lock_irqsave(bfqd->queue->queue_lock, *flags);
-		if (ptr == NULL)
-			printk(KERN_CRIT "get_bfqd_locked pointer NULL\n");
-		else if (*ptr == bfqd)
-			goto out;
-		spin_unlock_irqrestore(bfqd->queue->queue_lock, *flags);
-	}
-
-	bfqd = NULL;
-out:
-	rcu_read_unlock();
-	return bfqd;
-}
-
-static void bfq_put_bfqd_unlock(struct bfq_data *bfqd, unsigned long *flags)
-{
-	spin_unlock_irqrestore(bfqd->queue->queue_lock, *flags);
-}
-
 #ifdef CONFIG_BFQ_GROUP_IOSCHED
 
 static struct bfq_group *bfq_bfqq_to_bfqg(struct bfq_queue *bfqq)
@@ -857,11 +843,13 @@ static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio);
 static void bfq_put_queue(struct bfq_queue *bfqq);
 static void bfq_dispatch_insert(struct request_queue *q, struct request *rq);
 static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
-				       struct bio *bio, int is_sync,
-				       struct bfq_io_cq *bic, gfp_t gfp_mask);
+				       struct bio *bio, bool is_sync,
+				       struct bfq_io_cq *bic);
 static void bfq_end_wr_async_queues(struct bfq_data *bfqd,
 				    struct bfq_group *bfqg);
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
 static void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg);
+#endif
 static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq);
 
 #endif /* _BFQ_H */