bfq-wf2q.c 52.3 KB
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/*
 * Hierarchical Budget Worst-case Fair Weighted Fair Queueing
 * (B-WF2Q+): hierarchical scheduling algorithm by which the BFQ I/O
 * scheduler schedules generic entities. The latter can represent
 * either single bfq queues (associated with processes) or groups of
 * bfq queues (associated with cgroups).
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License as
 *  published by the Free Software Foundation; either version 2 of the
 *  License, or (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  General Public License for more details.
 */
#include "bfq-iosched.h"

/**
 * bfq_gt - compare two timestamps.
 * @a: first ts.
 * @b: second ts.
 *
 * Return @a > @b, dealing with wrapping correctly.
 */
static int bfq_gt(u64 a, u64 b)
{
	return (s64)(a - b) > 0;
}

static struct bfq_entity *bfq_root_active_entity(struct rb_root *tree)
{
	struct rb_node *node = tree->rb_node;

	return rb_entry(node, struct bfq_entity, rb_node);
}

static unsigned int bfq_class_idx(struct bfq_entity *entity)
{
	struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);

	return bfqq ? bfqq->ioprio_class - 1 :
		BFQ_DEFAULT_GRP_CLASS - 1;
}

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static struct bfq_entity *bfq_lookup_next_entity(struct bfq_sched_data *sd,
						 bool expiration);
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static bool bfq_update_parent_budget(struct bfq_entity *next_in_service);

/**
 * bfq_update_next_in_service - update sd->next_in_service
 * @sd: sched_data for which to perform the update.
 * @new_entity: if not NULL, pointer to the entity whose activation,
 *		requeueing or repositionig triggered the invocation of
 *		this function.
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 * @expiration: id true, this function is being invoked after the
 *             expiration of the in-service entity
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 *
 * This function is called to update sd->next_in_service, which, in
 * its turn, may change as a consequence of the insertion or
 * extraction of an entity into/from one of the active trees of
 * sd. These insertions/extractions occur as a consequence of
 * activations/deactivations of entities, with some activations being
 * 'true' activations, and other activations being requeueings (i.e.,
 * implementing the second, requeueing phase of the mechanism used to
 * reposition an entity in its active tree; see comments on
 * __bfq_activate_entity and __bfq_requeue_entity for details). In
 * both the last two activation sub-cases, new_entity points to the
 * just activated or requeued entity.
 *
 * Returns true if sd->next_in_service changes in such a way that
 * entity->parent may become the next_in_service for its parent
 * entity.
 */
static bool bfq_update_next_in_service(struct bfq_sched_data *sd,
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				       struct bfq_entity *new_entity,
				       bool expiration)
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{
	struct bfq_entity *next_in_service = sd->next_in_service;
	bool parent_sched_may_change = false;
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	bool change_without_lookup = false;
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	/*
	 * If this update is triggered by the activation, requeueing
	 * or repositiong of an entity that does not coincide with
	 * sd->next_in_service, then a full lookup in the active tree
	 * can be avoided. In fact, it is enough to check whether the
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	 * just-modified entity has the same priority as
	 * sd->next_in_service, is eligible and has a lower virtual
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	 * finish time than sd->next_in_service. If this compound
	 * condition holds, then the new entity becomes the new
	 * next_in_service. Otherwise no change is needed.
	 */
	if (new_entity && new_entity != sd->next_in_service) {
		/*
		 * Flag used to decide whether to replace
		 * sd->next_in_service with new_entity. Tentatively
		 * set to true, and left as true if
		 * sd->next_in_service is NULL.
		 */
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		change_without_lookup = true;
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		/*
		 * If there is already a next_in_service candidate
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		 * entity, then compare timestamps to decide whether
		 * to replace sd->service_tree with new_entity.
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		 */
		if (next_in_service) {
			unsigned int new_entity_class_idx =
				bfq_class_idx(new_entity);
			struct bfq_service_tree *st =
				sd->service_tree + new_entity_class_idx;

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			change_without_lookup =
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				(new_entity_class_idx ==
				 bfq_class_idx(next_in_service)
				 &&
				 !bfq_gt(new_entity->start, st->vtime)
				 &&
				 bfq_gt(next_in_service->finish,
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					new_entity->finish));
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		}

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		if (change_without_lookup)
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			next_in_service = new_entity;
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	}

	if (!change_without_lookup) /* lookup needed */
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		next_in_service = bfq_lookup_next_entity(sd, expiration);
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	if (next_in_service) {
		bool new_budget_triggers_change =
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			bfq_update_parent_budget(next_in_service);

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		parent_sched_may_change = !sd->next_in_service ||
			new_budget_triggers_change;
	}

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	sd->next_in_service = next_in_service;

	if (!next_in_service)
		return parent_sched_may_change;

	return parent_sched_may_change;
}

#ifdef CONFIG_BFQ_GROUP_IOSCHED

struct bfq_group *bfq_bfqq_to_bfqg(struct bfq_queue *bfqq)
{
	struct bfq_entity *group_entity = bfqq->entity.parent;

	if (!group_entity)
		group_entity = &bfqq->bfqd->root_group->entity;

	return container_of(group_entity, struct bfq_group, entity);
}

/*
 * Returns true if this budget changes may let next_in_service->parent
 * become the next_in_service entity for its parent entity.
 */
static bool bfq_update_parent_budget(struct bfq_entity *next_in_service)
{
	struct bfq_entity *bfqg_entity;
	struct bfq_group *bfqg;
	struct bfq_sched_data *group_sd;
	bool ret = false;

	group_sd = next_in_service->sched_data;

	bfqg = container_of(group_sd, struct bfq_group, sched_data);
	/*
	 * bfq_group's my_entity field is not NULL only if the group
	 * is not the root group. We must not touch the root entity
	 * as it must never become an in-service entity.
	 */
	bfqg_entity = bfqg->my_entity;
	if (bfqg_entity) {
		if (bfqg_entity->budget > next_in_service->budget)
			ret = true;
		bfqg_entity->budget = next_in_service->budget;
	}

	return ret;
}

/*
 * This function tells whether entity stops being a candidate for next
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 * service, according to the restrictive definition of the field
 * next_in_service. In particular, this function is invoked for an
 * entity that is about to be set in service.
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 *
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 * If entity is a queue, then the entity is no longer a candidate for
 * next service according to the that definition, because entity is
 * about to become the in-service queue. This function then returns
 * true if entity is a queue.
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 *
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 * In contrast, entity could still be a candidate for next service if
 * it is not a queue, and has more than one active child. In fact,
 * even if one of its children is about to be set in service, other
 * active children may still be the next to serve, for the parent
 * entity, even according to the above definition. As a consequence, a
 * non-queue entity is not a candidate for next-service only if it has
 * only one active child. And only if this condition holds, then this
 * function returns true for a non-queue entity.
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 */
static bool bfq_no_longer_next_in_service(struct bfq_entity *entity)
{
	struct bfq_group *bfqg;

	if (bfq_entity_to_bfqq(entity))
		return true;

	bfqg = container_of(entity, struct bfq_group, entity);

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	/*
	 * The field active_entities does not always contain the
	 * actual number of active children entities: it happens to
	 * not account for the in-service entity in case the latter is
	 * removed from its active tree (which may get done after
	 * invoking the function bfq_no_longer_next_in_service in
	 * bfq_get_next_queue). Fortunately, here, i.e., while
	 * bfq_no_longer_next_in_service is not yet completed in
	 * bfq_get_next_queue, bfq_active_extract has not yet been
	 * invoked, and thus active_entities still coincides with the
	 * actual number of active entities.
	 */
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	if (bfqg->active_entities == 1)
		return true;

	return false;
}

#else /* CONFIG_BFQ_GROUP_IOSCHED */

struct bfq_group *bfq_bfqq_to_bfqg(struct bfq_queue *bfqq)
{
	return bfqq->bfqd->root_group;
}

static bool bfq_update_parent_budget(struct bfq_entity *next_in_service)
{
	return false;
}

static bool bfq_no_longer_next_in_service(struct bfq_entity *entity)
{
	return true;
}

#endif /* CONFIG_BFQ_GROUP_IOSCHED */

/*
 * Shift for timestamp calculations.  This actually limits the maximum
 * service allowed in one timestamp delta (small shift values increase it),
 * the maximum total weight that can be used for the queues in the system
 * (big shift values increase it), and the period of virtual time
 * wraparounds.
 */
#define WFQ_SERVICE_SHIFT	22

struct bfq_queue *bfq_entity_to_bfqq(struct bfq_entity *entity)
{
	struct bfq_queue *bfqq = NULL;

	if (!entity->my_sched_data)
		bfqq = container_of(entity, struct bfq_queue, entity);

	return bfqq;
}


/**
 * bfq_delta - map service into the virtual time domain.
 * @service: amount of service.
 * @weight: scale factor (weight of an entity or weight sum).
 */
static u64 bfq_delta(unsigned long service, unsigned long weight)
{
	u64 d = (u64)service << WFQ_SERVICE_SHIFT;

	do_div(d, weight);
	return d;
}

/**
 * bfq_calc_finish - assign the finish time to an entity.
 * @entity: the entity to act upon.
 * @service: the service to be charged to the entity.
 */
static void bfq_calc_finish(struct bfq_entity *entity, unsigned long service)
{
	struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);

	entity->finish = entity->start +
		bfq_delta(service, entity->weight);

	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));
	}
}

/**
 * bfq_entity_of - get an entity from a node.
 * @node: the node field of the entity.
 *
 * Convert a node pointer to the relative entity.  This is used only
 * to simplify the logic of some functions and not as the generic
 * conversion mechanism because, e.g., in the tree walking functions,
 * the check for a %NULL value would be redundant.
 */
struct bfq_entity *bfq_entity_of(struct rb_node *node)
{
	struct bfq_entity *entity = NULL;

	if (node)
		entity = rb_entry(node, struct bfq_entity, rb_node);

	return entity;
}

/**
 * bfq_extract - remove an entity from a tree.
 * @root: the tree root.
 * @entity: the entity to remove.
 */
static void bfq_extract(struct rb_root *root, struct bfq_entity *entity)
{
	entity->tree = NULL;
	rb_erase(&entity->rb_node, root);
}

/**
 * bfq_idle_extract - extract an entity from the idle tree.
 * @st: the service tree of the owning @entity.
 * @entity: the entity being removed.
 */
static void bfq_idle_extract(struct bfq_service_tree *st,
			     struct bfq_entity *entity)
{
	struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
	struct rb_node *next;

	if (entity == st->first_idle) {
		next = rb_next(&entity->rb_node);
		st->first_idle = bfq_entity_of(next);
	}

	if (entity == st->last_idle) {
		next = rb_prev(&entity->rb_node);
		st->last_idle = bfq_entity_of(next);
	}

	bfq_extract(&st->idle, entity);

	if (bfqq)
		list_del(&bfqq->bfqq_list);
}

/**
 * bfq_insert - generic tree insertion.
 * @root: tree root.
 * @entity: entity to insert.
 *
 * This is used for the idle and the active tree, since they are both
 * ordered by finish time.
 */
static void bfq_insert(struct rb_root *root, struct bfq_entity *entity)
{
	struct bfq_entity *entry;
	struct rb_node **node = &root->rb_node;
	struct rb_node *parent = NULL;

	while (*node) {
		parent = *node;
		entry = rb_entry(parent, struct bfq_entity, rb_node);

		if (bfq_gt(entry->finish, entity->finish))
			node = &parent->rb_left;
		else
			node = &parent->rb_right;
	}

	rb_link_node(&entity->rb_node, parent, node);
	rb_insert_color(&entity->rb_node, root);

	entity->tree = root;
}

/**
 * bfq_update_min - update the min_start field of a entity.
 * @entity: the entity to update.
 * @node: one of its children.
 *
 * This function is called when @entity may store an invalid value for
 * min_start due to updates to the active tree.  The function  assumes
 * that the subtree rooted at @node (which may be its left or its right
 * child) has a valid min_start value.
 */
static void bfq_update_min(struct bfq_entity *entity, struct rb_node *node)
{
	struct bfq_entity *child;

	if (node) {
		child = rb_entry(node, struct bfq_entity, rb_node);
		if (bfq_gt(entity->min_start, child->min_start))
			entity->min_start = child->min_start;
	}
}

/**
 * bfq_update_active_node - recalculate min_start.
 * @node: the node to update.
 *
 * @node may have changed position or one of its children may have moved,
 * this function updates its min_start value.  The left and right subtrees
 * are assumed to hold a correct min_start value.
 */
static void bfq_update_active_node(struct rb_node *node)
{
	struct bfq_entity *entity = rb_entry(node, struct bfq_entity, rb_node);

	entity->min_start = entity->start;
	bfq_update_min(entity, node->rb_right);
	bfq_update_min(entity, node->rb_left);
}

/**
 * bfq_update_active_tree - update min_start for the whole active tree.
 * @node: the starting node.
 *
 * @node must be the deepest modified node after an update.  This function
 * updates its min_start using the values held by its children, assuming
 * that they did not change, and then updates all the nodes that may have
 * changed in the path to the root.  The only nodes that may have changed
 * are the ones in the path or their siblings.
 */
static void bfq_update_active_tree(struct rb_node *node)
{
	struct rb_node *parent;

up:
	bfq_update_active_node(node);

	parent = rb_parent(node);
	if (!parent)
		return;

	if (node == parent->rb_left && parent->rb_right)
		bfq_update_active_node(parent->rb_right);
	else if (parent->rb_left)
		bfq_update_active_node(parent->rb_left);

	node = parent;
	goto up;
}

/**
 * bfq_active_insert - insert an entity in the active tree of its
 *                     group/device.
 * @st: the service tree of the entity.
 * @entity: the entity being inserted.
 *
 * The active tree is ordered by finish time, but an extra key is kept
 * per each node, containing the minimum value for the start times of
 * its children (and the node itself), so it's possible to search for
 * the eligible node with the lowest finish time in logarithmic time.
 */
static void bfq_active_insert(struct bfq_service_tree *st,
			      struct bfq_entity *entity)
{
	struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
	struct rb_node *node = &entity->rb_node;
#ifdef CONFIG_BFQ_GROUP_IOSCHED
	struct bfq_sched_data *sd = NULL;
	struct bfq_group *bfqg = NULL;
	struct bfq_data *bfqd = NULL;
#endif

	bfq_insert(&st->active, entity);

	if (node->rb_left)
		node = node->rb_left;
	else if (node->rb_right)
		node = node->rb_right;

	bfq_update_active_tree(node);

#ifdef CONFIG_BFQ_GROUP_IOSCHED
	sd = entity->sched_data;
	bfqg = container_of(sd, struct bfq_group, sched_data);
	bfqd = (struct bfq_data *)bfqg->bfqd;
#endif
	if (bfqq)
		list_add(&bfqq->bfqq_list, &bfqq->bfqd->active_list);
#ifdef CONFIG_BFQ_GROUP_IOSCHED
	if (bfqg != bfqd->root_group)
		bfqg->active_entities++;
#endif
}

/**
 * bfq_ioprio_to_weight - calc a weight from an ioprio.
 * @ioprio: the ioprio value to convert.
 */
unsigned short bfq_ioprio_to_weight(int ioprio)
{
	return (IOPRIO_BE_NR - ioprio) * BFQ_WEIGHT_CONVERSION_COEFF;
}

/**
 * bfq_weight_to_ioprio - calc an ioprio from a weight.
 * @weight: the weight value to convert.
 *
 * To preserve as much as possible the old only-ioprio user interface,
 * 0 is used as an escape ioprio value for weights (numerically) equal or
 * larger than IOPRIO_BE_NR * BFQ_WEIGHT_CONVERSION_COEFF.
 */
static unsigned short bfq_weight_to_ioprio(int weight)
{
	return max_t(int, 0,
		     IOPRIO_BE_NR * BFQ_WEIGHT_CONVERSION_COEFF - weight);
}

static void bfq_get_entity(struct bfq_entity *entity)
{
	struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);

	if (bfqq) {
		bfqq->ref++;
		bfq_log_bfqq(bfqq->bfqd, bfqq, "get_entity: %p %d",
			     bfqq, bfqq->ref);
	}
}

/**
 * bfq_find_deepest - find the deepest node that an extraction can modify.
 * @node: the node being removed.
 *
 * Do the first step of an extraction in an rb tree, looking for the
 * node that will replace @node, and returning the deepest node that
 * the following modifications to the tree can touch.  If @node is the
 * last node in the tree return %NULL.
 */
static struct rb_node *bfq_find_deepest(struct rb_node *node)
{
	struct rb_node *deepest;

	if (!node->rb_right && !node->rb_left)
		deepest = rb_parent(node);
	else if (!node->rb_right)
		deepest = node->rb_left;
	else if (!node->rb_left)
		deepest = node->rb_right;
	else {
		deepest = rb_next(node);
		if (deepest->rb_right)
			deepest = deepest->rb_right;
		else if (rb_parent(deepest) != node)
			deepest = rb_parent(deepest);
	}

	return deepest;
}

/**
 * bfq_active_extract - remove an entity from the active tree.
 * @st: the service_tree containing the tree.
 * @entity: the entity being removed.
 */
static void bfq_active_extract(struct bfq_service_tree *st,
			       struct bfq_entity *entity)
{
	struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
	struct rb_node *node;
#ifdef CONFIG_BFQ_GROUP_IOSCHED
	struct bfq_sched_data *sd = NULL;
	struct bfq_group *bfqg = NULL;
	struct bfq_data *bfqd = NULL;
#endif

	node = bfq_find_deepest(&entity->rb_node);
	bfq_extract(&st->active, entity);

	if (node)
		bfq_update_active_tree(node);

#ifdef CONFIG_BFQ_GROUP_IOSCHED
	sd = entity->sched_data;
	bfqg = container_of(sd, struct bfq_group, sched_data);
	bfqd = (struct bfq_data *)bfqg->bfqd;
#endif
	if (bfqq)
		list_del(&bfqq->bfqq_list);
#ifdef CONFIG_BFQ_GROUP_IOSCHED
	if (bfqg != bfqd->root_group)
		bfqg->active_entities--;
#endif
}

/**
 * bfq_idle_insert - insert an entity into the idle tree.
 * @st: the service tree containing the tree.
 * @entity: the entity to insert.
 */
static void bfq_idle_insert(struct bfq_service_tree *st,
			    struct bfq_entity *entity)
{
	struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
	struct bfq_entity *first_idle = st->first_idle;
	struct bfq_entity *last_idle = st->last_idle;

	if (!first_idle || bfq_gt(first_idle->finish, entity->finish))
		st->first_idle = entity;
	if (!last_idle || bfq_gt(entity->finish, last_idle->finish))
		st->last_idle = entity;

	bfq_insert(&st->idle, entity);

	if (bfqq)
		list_add(&bfqq->bfqq_list, &bfqq->bfqd->idle_list);
}

/**
 * bfq_forget_entity - do not consider entity any longer for scheduling
 * @st: the service tree.
 * @entity: the entity being removed.
 * @is_in_service: true if entity is currently the in-service entity.
 *
 * Forget everything about @entity. In addition, if entity represents
 * a queue, and the latter is not in service, then release the service
 * reference to the queue (the one taken through bfq_get_entity). In
 * fact, in this case, there is really no more service reference to
 * the queue, as the latter is also outside any service tree. If,
 * instead, the queue is in service, then __bfq_bfqd_reset_in_service
 * will take care of putting the reference when the queue finally
 * stops being served.
 */
static void bfq_forget_entity(struct bfq_service_tree *st,
			      struct bfq_entity *entity,
			      bool is_in_service)
{
	struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);

	entity->on_st = false;
	st->wsum -= entity->weight;
	if (bfqq && !is_in_service)
		bfq_put_queue(bfqq);
}

/**
 * bfq_put_idle_entity - release the idle tree ref of an entity.
 * @st: service tree for the entity.
 * @entity: the entity being released.
 */
void bfq_put_idle_entity(struct bfq_service_tree *st, struct bfq_entity *entity)
{
	bfq_idle_extract(st, entity);
	bfq_forget_entity(st, entity,
			  entity == entity->sched_data->in_service_entity);
}

/**
 * bfq_forget_idle - update the idle tree if necessary.
 * @st: the service tree to act upon.
 *
 * To preserve the global O(log N) complexity we only remove one entry here;
 * as the idle tree will not grow indefinitely this can be done safely.
 */
static void bfq_forget_idle(struct bfq_service_tree *st)
{
	struct bfq_entity *first_idle = st->first_idle;
	struct bfq_entity *last_idle = st->last_idle;

	if (RB_EMPTY_ROOT(&st->active) && last_idle &&
	    !bfq_gt(last_idle->finish, st->vtime)) {
		/*
		 * Forget the whole idle tree, increasing the vtime past
		 * the last finish time of idle entities.
		 */
		st->vtime = last_idle->finish;
	}

	if (first_idle && !bfq_gt(first_idle->finish, st->vtime))
		bfq_put_idle_entity(st, first_idle);
}

struct bfq_service_tree *bfq_entity_service_tree(struct bfq_entity *entity)
{
	struct bfq_sched_data *sched_data = entity->sched_data;
	unsigned int idx = bfq_class_idx(entity);

	return sched_data->service_tree + idx;
}

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/*
 * Update weight and priority of entity. If update_class_too is true,
 * then update the ioprio_class of entity too.
 *
 * The reason why the update of ioprio_class is controlled through the
 * last parameter is as follows. Changing the ioprio class of an
 * entity implies changing the destination service trees for that
 * entity. If such a change occurred when the entity is already on one
 * of the service trees for its previous class, then the state of the
 * entity would become more complex: none of the new possible service
 * trees for the entity, according to bfq_entity_service_tree(), would
 * match any of the possible service trees on which the entity
 * is. Complex operations involving these trees, such as entity
 * activations and deactivations, should take into account this
 * additional complexity.  To avoid this issue, this function is
 * invoked with update_class_too unset in the points in the code where
 * entity may happen to be on some tree.
 */
723 724
struct bfq_service_tree *
__bfq_entity_update_weight_prio(struct bfq_service_tree *old_st,
725 726
				struct bfq_entity *entity,
				bool update_class_too)
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{
	struct bfq_service_tree *new_st = old_st;

	if (entity->prio_changed) {
		struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
		unsigned int prev_weight, new_weight;
		struct bfq_data *bfqd = NULL;
		struct rb_root *root;
#ifdef CONFIG_BFQ_GROUP_IOSCHED
		struct bfq_sched_data *sd;
		struct bfq_group *bfqg;
#endif

		if (bfqq)
			bfqd = bfqq->bfqd;
#ifdef CONFIG_BFQ_GROUP_IOSCHED
		else {
			sd = entity->my_sched_data;
			bfqg = container_of(sd, struct bfq_group, sched_data);
			bfqd = (struct bfq_data *)bfqg->bfqd;
		}
#endif

		old_st->wsum -= entity->weight;

		if (entity->new_weight != entity->orig_weight) {
			if (entity->new_weight < BFQ_MIN_WEIGHT ||
			    entity->new_weight > BFQ_MAX_WEIGHT) {
				pr_crit("update_weight_prio: new_weight %d\n",
					entity->new_weight);
				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;
			if (bfqq)
				bfqq->ioprio =
				  bfq_weight_to_ioprio(entity->orig_weight);
		}

768
		if (bfqq && update_class_too)
769
			bfqq->ioprio_class = bfqq->new_ioprio_class;
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		/*
		 * Reset prio_changed only if the ioprio_class change
		 * is not pending any longer.
		 */
		if (!bfqq || bfqq->ioprio_class == bfqq->new_ioprio_class)
			entity->prio_changed = 0;
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		/*
		 * NOTE: here we may be changing the weight too early,
		 * this will cause unfairness.  The correct approach
		 * would have required additional complexity to defer
		 * weight changes to the proper time instants (i.e.,
		 * when entity->finish <= old_st->vtime).
		 */
		new_st = bfq_entity_service_tree(entity);

		prev_weight = entity->weight;
		new_weight = entity->orig_weight *
			     (bfqq ? bfqq->wr_coeff : 1);
		/*
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		 * If the weight of the entity changes, and the entity is a
		 * queue, remove the entity from its old weight counter (if
		 * there is a counter associated with the entity).
794
		 */
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		if (prev_weight != new_weight && bfqq) {
			root = &bfqd->queue_weights_tree;
			__bfq_weights_tree_remove(bfqd, bfqq, root);
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		}
		entity->weight = new_weight;
		/*
801 802
		 * Add the entity, if it is not a weight-raised queue,
		 * to the counter associated with its new weight.
803
		 */
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		if (prev_weight != new_weight && bfqq && bfqq->wr_coeff == 1) {
			/* If we get here, root has been initialized. */
			bfq_weights_tree_add(bfqd, bfqq, root);
807
		}
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		new_st->wsum += entity->weight;

		if (new_st != old_st)
			entity->start = new_st->vtime;
	}

	return new_st;
}

/**
 * bfq_bfqq_served - update the scheduler status after selection for
 *                   service.
 * @bfqq: the queue being served.
 * @served: bytes to transfer.
 *
 * NOTE: this can be optimized, as the timestamps of upper level entities
 * are synchronized every time a new bfqq is selected for service.  By now,
 * we keep it to better check consistency.
 */
void bfq_bfqq_served(struct bfq_queue *bfqq, int served)
{
	struct bfq_entity *entity = &bfqq->entity;
	struct bfq_service_tree *st;

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	if (!bfqq->service_from_backlogged)
		bfqq->first_IO_time = jiffies;

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	if (bfqq->wr_coeff > 1)
		bfqq->service_from_wr += served;

839
	bfqq->service_from_backlogged += served;
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	for_each_entity(entity) {
		st = bfq_entity_service_tree(entity);

		entity->service += served;

		st->vtime += bfq_delta(served, st->wsum);
		bfq_forget_idle(st);
	}
	bfq_log_bfqq(bfqq->bfqd, bfqq, "bfqq_served %d secs", served);
}

/**
 * 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
 *
 * 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.
 */
void bfq_bfqq_charge_time(struct bfq_data *bfqd, struct bfq_queue *bfqq,
			  unsigned long time_ms)
{
	struct bfq_entity *entity = &bfqq->entity;
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	unsigned long timeout_ms = jiffies_to_msecs(bfq_timeout);
	unsigned long bounded_time_ms = min(time_ms, timeout_ms);
	int serv_to_charge_for_time =
		(bfqd->bfq_max_budget * bounded_time_ms) / timeout_ms;
	int tot_serv_to_charge = max(serv_to_charge_for_time, entity->service);
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	/* 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));
}

static void bfq_update_fin_time_enqueue(struct bfq_entity *entity,
					struct bfq_service_tree *st,
					bool backshifted)
{
	struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);

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	/*
	 * When this function is invoked, entity is not in any service
	 * tree, then it is safe to invoke next function with the last
	 * parameter set (see the comments on the function).
	 */
	st = __bfq_entity_update_weight_prio(st, entity, true);
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	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;
	}

	bfq_active_insert(st, entity);
}

/**
 * __bfq_activate_entity - handle activation of entity.
 * @entity: the entity being activated.
 * @non_blocking_wait_rq: true if entity was waiting for a request
 *
 * Called for a 'true' activation, i.e., if entity is not active and
 * one of its children receives a new request.
 *
 * Basically, this function updates the timestamps of entity and
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 * inserts entity into its active tree, after possibly extracting it
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 * from its idle tree.
 */
static void __bfq_activate_entity(struct bfq_entity *entity,
				  bool non_blocking_wait_rq)
{
	struct bfq_service_tree *st = bfq_entity_service_tree(entity);
	bool backshifted = false;
	unsigned long long min_vstart;

	/* 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;
		/*
		 * entity is about to be inserted into a service tree,
		 * and then set in service: get a reference to make
		 * sure entity does not disappear until it is no
		 * longer in service or scheduled for service.
		 */
		bfq_get_entity(entity);

		entity->on_st = true;
	}

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#ifdef BFQ_GROUP_IOSCHED_ENABLED
	if (!bfq_entity_to_bfqq(entity)) { /* bfq_group */
		struct bfq_group *bfqg =
			container_of(entity, struct bfq_group, entity);
1013
		struct bfq_data *bfqd = bfqg->bfqd;
1014

1015 1016 1017 1018
		if (!entity->in_groups_with_pending_reqs) {
			entity->in_groups_with_pending_reqs = true;
			bfqd->num_groups_with_pending_reqs++;
		}
1019 1020 1021
	}
#endif

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	bfq_update_fin_time_enqueue(entity, st, backshifted);
}

/**
 * __bfq_requeue_entity - handle requeueing or repositioning of an entity.
 * @entity: the entity being requeued or repositioned.
 *
 * Requeueing is needed if this entity stops being served, which
 * happens if a leaf descendant entity has expired. On the other hand,
 * repositioning is needed if the next_inservice_entity for the child
 * entity has changed. See the comments inside the function for
 * details.
 *
 * Basically, this function: 1) removes entity from its active tree if
 * present there, 2) updates the timestamps of entity and 3) inserts
 * entity back into its active tree (in the new, right position for
 * the new values of the timestamps).
 */
static void __bfq_requeue_entity(struct bfq_entity *entity)
{
	struct bfq_sched_data *sd = entity->sched_data;
	struct bfq_service_tree *st = bfq_entity_service_tree(entity);

	if (entity == sd->in_service_entity) {
		/*
		 * We are requeueing the current in-service entity,
		 * which may have to be done for one of the following
		 * reasons:
		 * - entity represents the in-service queue, and the
		 *   in-service queue is being requeued after an
		 *   expiration;
		 * - entity represents a group, and its budget has
		 *   changed because one of its child entities has
		 *   just been either activated or requeued for some
		 *   reason; the timestamps of the entity need then to
		 *   be updated, and the entity needs to be enqueued
		 *   or repositioned accordingly.
		 *
		 * In particular, before requeueing, the start time of
		 * the entity must be moved forward to account for the
		 * service that the entity has received while in
		 * service. This is done by the next instructions. The
		 * finish time will then be updated according to this
		 * new value of the start time, and to the budget of
		 * the entity.
		 */
		bfq_calc_finish(entity, entity->service);
		entity->start = entity->finish;
		/*
		 * In addition, if the entity had more than one child
1072
		 * when set in service, then it was not extracted from
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		 * the active tree. This implies that the position of
		 * the entity in the active tree may need to be
		 * changed now, because we have just updated the start
		 * time of the entity, and we will update its finish
		 * time in a moment (the requeueing is then, more
		 * precisely, a repositioning in this case). To
		 * implement this repositioning, we: 1) dequeue the
1080 1081
		 * entity here, 2) update the finish time and requeue
		 * the entity according to the new timestamps below.
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		 */
		if (entity->tree)
			bfq_active_extract(st, entity);
	} else { /* The entity is already active, and not in service */
		/*
		 * In this case, this function gets called only if the
		 * next_in_service entity below this entity has
		 * changed, and this change has caused the budget of
		 * this entity to change, which, finally implies that
		 * the finish time of this entity must be
		 * updated. Such an update may cause the scheduling,
		 * i.e., the position in the active tree, of this
		 * entity to change. We handle this change by: 1)
		 * dequeueing the entity here, 2) updating the finish
		 * time and requeueing the entity according to the new
		 * timestamps below. This is the same approach as the
		 * non-extracted-entity sub-case above.
		 */
		bfq_active_extract(st, entity);
	}

	bfq_update_fin_time_enqueue(entity, st, false);
}

static void __bfq_activate_requeue_entity(struct bfq_entity *entity,
					  struct bfq_sched_data *sd,
					  bool non_blocking_wait_rq)
{
	struct bfq_service_tree *st = bfq_entity_service_tree(entity);

	if (sd->in_service_entity == entity || entity->tree == &st->active)
		 /*
		  * in service or already queued on the active tree,
		  * requeue or reposition
		  */
		__bfq_requeue_entity(entity);
	else
		/*
		 * Not in service and not queued on its active tree:
		 * the activity is idle and this is a true activation.
		 */
		__bfq_activate_entity(entity, non_blocking_wait_rq);
}


/**
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 * bfq_activate_requeue_entity - activate or requeue an entity representing a
 *				 bfq_queue, and activate, requeue or reposition
 *				 all ancestors for which such an update becomes
 *				 necessary.
1132 1133 1134 1135 1136
 * @entity: the entity to activate.
 * @non_blocking_wait_rq: true if this entity was waiting for a request
 * @requeue: true if this is a requeue, which implies that bfqq is
 *	     being expired; thus ALL its ancestors stop being served and must
 *	     therefore be requeued
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 * @expiration: true if this function is being invoked in the expiration path
 *             of the in-service queue
1139 1140 1141
 */
static void bfq_activate_requeue_entity(struct bfq_entity *entity,
					bool non_blocking_wait_rq,
1142
					bool requeue, bool expiration)
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{
	struct bfq_sched_data *sd;

	for_each_entity(entity) {
		sd = entity->sched_data;
		__bfq_activate_requeue_entity(entity, sd, non_blocking_wait_rq);

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		if (!bfq_update_next_in_service(sd, entity, expiration) &&
		    !requeue)
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			break;
	}
}

/**
 * __bfq_deactivate_entity - deactivate an entity from its service tree.
 * @entity: the entity to deactivate.
 * @ins_into_idle_tree: if false, the entity will not be put into the
 *			idle tree.
 *
1162
 * Deactivates an entity, independently of its previous state.  Must
1163
 * be invoked only if entity is on a service tree. Extracts the entity
1164
 * from that tree, and if necessary and allowed, puts it into the idle
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 * tree.
 */
bool __bfq_deactivate_entity(struct bfq_entity *entity, bool ins_into_idle_tree)
{
	struct bfq_sched_data *sd = entity->sched_data;
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	struct bfq_service_tree *st;
	bool is_in_service;
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	if (!entity->on_st) /* entity never activated, or already inactive */
		return false;

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	/*
	 * If we get here, then entity is active, which implies that
	 * bfq_group_set_parent has already been invoked for the group
	 * represented by entity. Therefore, the field
	 * entity->sched_data has been set, and we can safely use it.
	 */
	st = bfq_entity_service_tree(entity);
	is_in_service = entity == sd->in_service_entity;

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	bfq_calc_finish(entity, entity->service);

	if (is_in_service)
1188
		sd->in_service_entity = NULL;
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	else
		/*
		 * Non in-service entity: nobody will take care of
		 * resetting its service counter on expiration. Do it
		 * now.
		 */
		entity->service = 0;
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	if (entity->tree == &st->active)
		bfq_active_extract(st, entity);
	else if (!is_in_service && entity->tree == &st->idle)
		bfq_idle_extract(st, entity);

	if (!ins_into_idle_tree || !bfq_gt(entity->finish, st->vtime))
		bfq_forget_entity(st, entity, is_in_service);
	else
		bfq_idle_insert(st, entity);

	return true;
}

/**
 * bfq_deactivate_entity - deactivate an entity representing a bfq_queue.
 * @entity: the entity to deactivate.
1213
 * @ins_into_idle_tree: true if the entity can be put into the idle tree
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 * @expiration: true if this function is being invoked in the expiration path
 *             of the in-service queue
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 */
static void bfq_deactivate_entity(struct bfq_entity *entity,
				  bool ins_into_idle_tree,
				  bool expiration)
{
	struct bfq_sched_data *sd;
	struct bfq_entity *parent = NULL;

	for_each_entity_safe(entity, parent) {
		sd = entity->sched_data;

		if (!__bfq_deactivate_entity(entity, ins_into_idle_tree)) {
			/*
			 * entity is not in any tree any more, so
			 * this deactivation is a no-op, and there is
			 * nothing to change for upper-level entities
			 * (in case of expiration, this can never
			 * happen).
			 */
			return;
		}

		if (sd->next_in_service == entity)
			/*
			 * entity was the next_in_service entity,
			 * then, since entity has just been
			 * deactivated, a new one must be found.
			 */
1244
			bfq_update_next_in_service(sd, NULL, expiration);
1245

1246
		if (sd->next_in_service || sd->in_service_entity) {
1247
			/*
1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265
			 * The parent entity is still active, because
			 * either next_in_service or in_service_entity
			 * is not NULL. So, no further upwards
			 * deactivation must be performed.  Yet,
			 * next_in_service has changed.	Then the
			 * schedule does need to be updated upwards.
			 *
			 * NOTE If in_service_entity is not NULL, then
			 * next_in_service may happen to be NULL,
			 * although the parent entity is evidently
			 * active. This happens if 1) the entity
			 * pointed by in_service_entity is the only
			 * active entity in the parent entity, and 2)
			 * according to the definition of
			 * next_in_service, the in_service_entity
			 * cannot be considered as
			 * next_in_service. See the comments on the
			 * definition of next_in_service for details.
1266 1267
			 */
			break;
1268
		}
1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302

		/*
		 * If we get here, then the parent is no more
		 * backlogged and we need to propagate the
		 * deactivation upwards. Thus let the loop go on.
		 */

		/*
		 * Also let parent be queued into the idle tree on
		 * deactivation, to preserve service guarantees, and
		 * assuming that who invoked this function does not
		 * need parent entities too to be removed completely.
		 */
		ins_into_idle_tree = true;
	}

	/*
	 * If the deactivation loop is fully executed, then there are
	 * no more entities to touch and next loop is not executed at
	 * all. Otherwise, requeue remaining entities if they are
	 * about to stop receiving service, or reposition them if this
	 * is not the case.
	 */
	entity = parent;
	for_each_entity(entity) {
		/*
		 * Invoke __bfq_requeue_entity on entity, even if
		 * already active, to requeue/reposition it in the
		 * active tree (because sd->next_in_service has
		 * changed)
		 */
		__bfq_requeue_entity(entity);

		sd = entity->sched_data;
1303
		if (!bfq_update_next_in_service(sd, entity, expiration) &&
1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347
		    !expiration)
			/*
			 * next_in_service unchanged or not causing
			 * any change in entity->parent->sd, and no
			 * requeueing needed for expiration: stop
			 * here.
			 */
			break;
	}
}

/**
 * bfq_calc_vtime_jump - compute the value to which the vtime should jump,
 *                       if needed, to have at least one entity eligible.
 * @st: the service tree to act upon.
 *
 * Assumes that st is not empty.
 */
static u64 bfq_calc_vtime_jump(struct bfq_service_tree *st)
{
	struct bfq_entity *root_entity = bfq_root_active_entity(&st->active);

	if (bfq_gt(root_entity->min_start, st->vtime))
		return root_entity->min_start;

	return st->vtime;
}

static void bfq_update_vtime(struct bfq_service_tree *st, u64 new_value)
{
	if (new_value > st->vtime) {
		st->vtime = new_value;
		bfq_forget_idle(st);
	}
}

/**
 * bfq_first_active_entity - find the eligible entity with
 *                           the smallest finish time
 * @st: the service tree to select from.
 * @vtime: the system virtual to use as a reference for eligibility
 *
 * This function searches the first schedulable entity, starting from the
 * root of the tree and going on the left every time on this side there is
1348
 * a subtree with at least one eligible (start <= vtime) entity. The path on
1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437
 * the right is followed only if a) the left subtree contains no eligible
 * entities and b) no eligible entity has been found yet.
 */
static struct bfq_entity *bfq_first_active_entity(struct bfq_service_tree *st,
						  u64 vtime)
{
	struct bfq_entity *entry, *first = NULL;
	struct rb_node *node = st->active.rb_node;

	while (node) {
		entry = rb_entry(node, struct bfq_entity, rb_node);
left:
		if (!bfq_gt(entry->start, vtime))
			first = entry;

		if (node->rb_left) {
			entry = rb_entry(node->rb_left,
					 struct bfq_entity, rb_node);
			if (!bfq_gt(entry->min_start, vtime)) {
				node = node->rb_left;
				goto left;
			}
		}
		if (first)
			break;
		node = node->rb_right;
	}

	return first;
}

/**
 * __bfq_lookup_next_entity - return the first eligible entity in @st.
 * @st: the service tree.
 *
 * If there is no in-service entity for the sched_data st belongs to,
 * then return the entity that will be set in service if:
 * 1) the parent entity this st belongs to is set in service;
 * 2) no entity belonging to such parent entity undergoes a state change
 * that would influence the timestamps of the entity (e.g., becomes idle,
 * becomes backlogged, changes its budget, ...).
 *
 * In this first case, update the virtual time in @st too (see the
 * comments on this update inside the function).
 *
 * In constrast, if there is an in-service entity, then return the
 * entity that would be set in service if not only the above
 * conditions, but also the next one held true: the currently
 * in-service entity, on expiration,
 * 1) gets a finish time equal to the current one, or
 * 2) is not eligible any more, or
 * 3) is idle.
 */
static struct bfq_entity *
__bfq_lookup_next_entity(struct bfq_service_tree *st, bool in_service)
{
	struct bfq_entity *entity;
	u64 new_vtime;

	if (RB_EMPTY_ROOT(&st->active))
		return NULL;

	/*
	 * Get the value of the system virtual time for which at
	 * least one entity is eligible.
	 */
	new_vtime = bfq_calc_vtime_jump(st);

	/*
	 * If there is no in-service entity for the sched_data this
	 * active tree belongs to, then push the system virtual time
	 * up to the value that guarantees that at least one entity is
	 * eligible. If, instead, there is an in-service entity, then
	 * do not make any such update, because there is already an
	 * eligible entity, namely the in-service one (even if the
	 * entity is not on st, because it was extracted when set in
	 * service).
	 */
	if (!in_service)
		bfq_update_vtime(st, new_vtime);

	entity = bfq_first_active_entity(st, new_vtime);

	return entity;
}

/**
 * bfq_lookup_next_entity - return the first eligible entity in @sd.
 * @sd: the sched_data.
1438
 * @expiration: true if we are on the expiration path of the in-service queue
1439 1440
 *
 * This function is invoked when there has been a change in the trees
1441 1442
 * for sd, and we need to know what is the new next entity to serve
 * after this change.
1443
 */
1444 1445
static struct bfq_entity *bfq_lookup_next_entity(struct bfq_sched_data *sd,
						 bool expiration)
1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471
{
	struct bfq_service_tree *st = sd->service_tree;
	struct bfq_service_tree *idle_class_st = st + (BFQ_IOPRIO_CLASSES - 1);
	struct bfq_entity *entity = NULL;
	int class_idx = 0;

	/*
	 * Choose from idle class, if needed to guarantee a minimum
	 * bandwidth to this class (and if there is some active entity
	 * in idle class). This should also mitigate
	 * priority-inversion problems in case a low priority task is
	 * holding file system resources.
	 */
	if (time_is_before_jiffies(sd->bfq_class_idle_last_service +
				   BFQ_CL_IDLE_TIMEOUT)) {
		if (!RB_EMPTY_ROOT(&idle_class_st->active))
			class_idx = BFQ_IOPRIO_CLASSES - 1;
		/* About to be served if backlogged, or not yet backlogged */
		sd->bfq_class_idle_last_service = jiffies;
	}

	/*
	 * Find the next entity to serve for the highest-priority
	 * class, unless the idle class needs to be served.
	 */
	for (; class_idx < BFQ_IOPRIO_CLASSES; class_idx++) {
1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486
		/*
		 * If expiration is true, then bfq_lookup_next_entity
		 * is being invoked as a part of the expiration path
		 * of the in-service queue. In this case, even if
		 * sd->in_service_entity is not NULL,
		 * sd->in_service_entiy at this point is actually not
		 * in service any more, and, if needed, has already
		 * been properly queued or requeued into the right
		 * tree. The reason why sd->in_service_entity is still
		 * not NULL here, even if expiration is true, is that
		 * sd->in_service_entiy is reset as a last step in the
		 * expiration path. So, if expiration is true, tell
		 * __bfq_lookup_next_entity that there is no
		 * sd->in_service_entity.
		 */
1487
		entity = __bfq_lookup_next_entity(st + class_idx,
1488 1489
						  sd->in_service_entity &&
						  !expiration);
1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556

		if (entity)
			break;
	}

	if (!entity)
		return NULL;

	return entity;
}

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.
 */
struct bfq_queue *bfq_get_next_queue(struct bfq_data *bfqd)
{
	struct bfq_entity *entity = NULL;
	struct bfq_sched_data *sd;
	struct bfq_queue *bfqq;

	if (bfqd->busy_queues == 0)
		return NULL;

	/*
	 * Traverse the path from the root to the leaf entity to
	 * serve. Set in service all the entities visited along the
	 * way.
	 */
	sd = &bfqd->root_group->sched_data;
	for (; sd ; sd = entity->my_sched_data) {
		/*
		 * WARNING. We are about to set the in-service entity
		 * to sd->next_in_service, i.e., to the (cached) value
		 * returned by bfq_lookup_next_entity(sd) the last
		 * time it was invoked, i.e., the last time when the
		 * service order in sd changed as a consequence of the
		 * activation or deactivation of an entity. In this
		 * respect, if we execute bfq_lookup_next_entity(sd)
		 * in this very moment, it may, although with low
		 * probability, yield a different entity than that
		 * pointed to by sd->next_in_service. This rare event
		 * happens in case there was no CLASS_IDLE entity to
		 * serve for sd when bfq_lookup_next_entity(sd) was
		 * invoked for the last time, while there is now one
		 * such entity.
		 *
		 * If the above event happens, then the scheduling of
		 * such entity in CLASS_IDLE is postponed until the
		 * service of the sd->next_in_service entity
		 * finishes. In fact, when the latter is expired,
		 * bfq_lookup_next_entity(sd) gets called again,
		 * exactly to update sd->next_in_service.
		 */

		/* Make next_in_service entity become in_service_entity */
		entity = sd->next_in_service;
		sd->in_service_entity = entity;

		/*
		 * If entity is no longer a candidate for next
1557 1558 1559 1560 1561
		 * service, then it must be extracted from its active
		 * tree, so as to make sure that it won't be
		 * considered when computing next_in_service. See the
		 * comments on the function
		 * bfq_no_longer_next_in_service() for details.
1562 1563 1564 1565 1566 1567
		 */
		if (bfq_no_longer_next_in_service(entity))
			bfq_active_extract(bfq_entity_service_tree(entity),
					   entity);

		/*
1568 1569 1570 1571 1572 1573
		 * Even if entity is not to be extracted according to
		 * the above check, a descendant entity may get
		 * extracted in one of the next iterations of this
		 * loop. Such an event could cause a change in
		 * next_in_service for the level of the descendant
		 * entity, and thus possibly back to this level.
1574
		 *
1575 1576 1577 1578 1579 1580 1581 1582 1583
		 * However, we cannot perform the resulting needed
		 * update of next_in_service for this level before the
		 * end of the whole loop, because, to know which is
		 * the correct next-to-serve candidate entity for each
		 * level, we need first to find the leaf entity to set
		 * in service. In fact, only after we know which is
		 * the next-to-serve leaf entity, we can discover
		 * whether the parent entity of the leaf entity
		 * becomes the next-to-serve, and so on.
1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595
		 */
	}

	bfqq = bfq_entity_to_bfqq(entity);

	/*
	 * We can finally update all next-to-serve entities along the
	 * path from the leaf entity just set in service to the root.
	 */
	for_each_entity(entity) {
		struct bfq_sched_data *sd = entity->sched_data;

1596
		if (!bfq_update_next_in_service(sd, NULL, false))
1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643
			break;
	}

	return bfqq;
}

void __bfq_bfqd_reset_in_service(struct bfq_data *bfqd)
{
	struct bfq_queue *in_serv_bfqq = bfqd->in_service_queue;
	struct bfq_entity *in_serv_entity = &in_serv_bfqq->entity;
	struct bfq_entity *entity = in_serv_entity;

	bfq_clear_bfqq_wait_request(in_serv_bfqq);
	hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
	bfqd->in_service_queue = NULL;

	/*
	 * When this function is called, all in-service entities have
	 * been properly deactivated or requeued, so we can safely
	 * execute the final step: reset in_service_entity along the
	 * path from entity to the root.
	 */
	for_each_entity(entity)
		entity->sched_data->in_service_entity = NULL;

	/*
	 * in_serv_entity is no longer in service, so, if it is in no
	 * service tree either, then release the service reference to
	 * the queue it represents (taken with bfq_get_entity).
	 */
	if (!in_serv_entity->on_st)
		bfq_put_queue(in_serv_bfqq);
}

void bfq_deactivate_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
			 bool ins_into_idle_tree, bool expiration)
{
	struct bfq_entity *entity = &bfqq->entity;

	bfq_deactivate_entity(entity, ins_into_idle_tree, expiration);
}

void bfq_activate_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
{
	struct bfq_entity *entity = &bfqq->entity;

	bfq_activate_requeue_entity(entity, bfq_bfqq_non_blocking_wait_rq(bfqq),
1644
				    false, false);
1645 1646 1647
	bfq_clear_bfqq_non_blocking_wait_rq(bfqq);
}

1648 1649
void bfq_requeue_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
		      bool expiration)
1650 1651 1652 1653
{
	struct bfq_entity *entity = &bfqq->entity;

	bfq_activate_requeue_entity(entity, false,
1654
				    bfqq == bfqd->in_service_queue, expiration);
1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671
}

/*
 * Called when the bfqq no longer has requests pending, remove it from
 * the service tree. As a special case, it can be invoked during an
 * expiration.
 */
void bfq_del_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq,
		       bool expiration)
{
	bfq_log_bfqq(bfqd, bfqq, "del from busy");

	bfq_clear_bfqq_busy(bfqq);

	bfqd->busy_queues--;

	if (!bfqq->dispatched)
1672
		bfq_weights_tree_remove(bfqd, bfqq);
1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695

	if (bfqq->wr_coeff > 1)
		bfqd->wr_busy_queues--;

	bfqg_stats_update_dequeue(bfqq_group(bfqq));

	bfq_deactivate_bfqq(bfqd, bfqq, true, expiration);
}

/*
 * Called when an inactive queue receives a new request.
 */
void bfq_add_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq)
{
	bfq_log_bfqq(bfqd, bfqq, "add to busy");

	bfq_activate_bfqq(bfqd, bfqq);

	bfq_mark_bfqq_busy(bfqq);
	bfqd->busy_queues++;

	if (!bfqq->dispatched)
		if (bfqq->wr_coeff == 1)
1696
			bfq_weights_tree_add(bfqd, bfqq,
1697 1698 1699 1700 1701
					     &bfqd->queue_weights_tree);

	if (bfqq->wr_coeff > 1)
		bfqd->wr_busy_queues++;
}