text: /*
   * 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;
  }
  
  static struct bfq_entity *bfq_lookup_next_entity(struct bfq_sched_data *sd,
  						 bool expiration);
  
  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.
   * @expiration: id true, this function is being invoked after the
   *             expiration of the in-service entity
   *
   * 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,
  				       struct bfq_entity *new_entity,
  				       bool expiration)
  {
  	struct bfq_entity *next_in_service = sd->next_in_service;
  	bool parent_sched_may_change = false;
  	bool change_without_lookup = false;
  
  	/*
  	 * 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
  	 * just-modified entity has the same priority as
  	 * sd->next_in_service, is eligible and has a lower virtual
  	 * 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.
  		 */
  		change_without_lookup = true;
  
  		/*
  		 * If there is already a next_in_service candidate
  		 * entity, then compare timestamps to decide whether
  		 * to replace sd->service_tree with new_entity.
  		 */
  		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;
  
  			change_without_lookup =
  				(new_entity_class_idx ==
  				 bfq_class_idx(next_in_service)
  				 &&
  				 !bfq_gt(new_entity->start, st->vtime)
  				 &&
  				 bfq_gt(next_in_service->finish,
  					new_entity->finish));
  		}
  
  		if (change_without_lookup)
  			next_in_service = new_entity;
  	}
  
  	if (!change_without_lookup) /* lookup needed */
  		next_in_service = bfq_lookup_next_entity(sd, expiration);
  
  	if (next_in_service)
  		parent_sched_may_change = !sd->next_in_service ||
  			bfq_update_parent_budget(next_in_service);
  
  	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
   * 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.
   *
   * 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.
   *
   * 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.
   */
  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);
  
  	/*
  	 * 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.
  	 */
  	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
  	else /* bfq_group */
  		bfq_weights_tree_add(bfqd, entity, &bfqd->group_weights_tree);
  
  	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
  	else /* bfq_group */
  		bfq_weights_tree_remove(bfqd, entity,
  					&bfqd->group_weights_tree);
  
  	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;
  }
  
  /*
   * 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.
   */
  struct bfq_service_tree *
  __bfq_entity_update_weight_prio(struct bfq_service_tree *old_st,
  				struct bfq_entity *entity,
  				bool update_class_too)
  {
  	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);
  		}
  
  		if (bfqq && update_class_too)
  			bfqq->ioprio_class = bfqq->new_ioprio_class;
  
  		/*
  		 * 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;
  
  		/*
  		 * 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);
  		/*
  		 * If the weight of the entity changes, remove the entity
  		 * from its old weight counter (if there is a counter
  		 * associated with the entity), and add it to the counter
  		 * associated with its new weight.
  		 */
  		if (prev_weight != new_weight) {
  			root = bfqq ? &bfqd->queue_weights_tree :
  				      &bfqd->group_weights_tree;
  			bfq_weights_tree_remove(bfqd, entity, root);
  		}
  		entity->weight = new_weight;
  		/*
  		 * Add the entity to its weights tree only if it is
  		 * not associated with a weight-raised queue.
  		 */
  		if (prev_weight != new_weight &&
  		    (bfqq ? bfqq->wr_coeff == 1 : 1))
  			/* If we get here, root has been initialized. */
  			bfq_weights_tree_add(bfqd, entity, root);
  
  		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;
  
  	if (!bfqq->service_from_backlogged)
  		bfqq->first_IO_time = jiffies;
  
  	if (bfqq->wr_coeff > 1)
  		bfqq->service_from_wr += served;
  
  	bfqq->service_from_backlogged += served;
  	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;
  	int tot_serv_to_charge = entity->service;
  	unsigned int timeout_ms = jiffies_to_msecs(bfq_timeout);
  
  	if (time_ms > 0 && time_ms < timeout_ms)
  		tot_serv_to_charge =
  			(bfqd->bfq_max_budget * time_ms) / timeout_ms;
  
  	if (tot_serv_to_charge < entity->service)
  		tot_serv_to_charge = entity->service;
  
  	/* 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);
  
  	/*
  	 * 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);
  	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
   * inserts entity into its active tree, ater possibly extracting it
   * 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;
  	}
  
  	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
  		 * when set in service, then it was not extracted from
  		 * 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
  		 * entity here, 2) update the finish time and requeue
  		 * the entity according to the new timestamps below.
  		 */
  		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);
  }
  
  
  /**
   * 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.
   * @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
   * @expiration: true if this function is being invoked in the expiration path
   *             of the in-service queue
   */
  static void bfq_activate_requeue_entity(struct bfq_entity *entity,
  					bool non_blocking_wait_rq,
  					bool requeue, bool expiration)
  {
  	struct bfq_sched_data *sd;
  
  	for_each_entity(entity) {
  		sd = entity->sched_data;
  		__bfq_activate_requeue_entity(entity, sd, non_blocking_wait_rq);
  
  		if (!bfq_update_next_in_service(sd, entity, expiration) &&
  		    !requeue)
  			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.
   *
   * Deactivates an entity, independently of its previous state.  Must
   * be invoked only if entity is on a service tree. Extracts the entity
   * from that tree, and if necessary and allowed, puts it into the idle
   * tree.
   */
  bool __bfq_deactivate_entity(struct bfq_entity *entity, bool ins_into_idle_tree)
  {
  	struct bfq_sched_data *sd = entity->sched_data;
  	struct bfq_service_tree *st;
  	bool is_in_service;
  
  	if (!entity->on_st) /* entity never activated, or already inactive */
  		return false;
  
  	/*
  	 * 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;
  
  	if (is_in_service) {
  		bfq_calc_finish(entity, entity->service);
  		sd->in_service_entity = NULL;
  	}
  
  	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.
   * @ins_into_idle_tree: true if the entity can be put into the idle tree
   * @expiration: true if this function is being invoked in the expiration path
   *             of the in-service queue
   */
  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.
  			 */
  			bfq_update_next_in_service(sd, NULL, expiration);
  
  		if (sd->next_in_service || sd->in_service_entity) {
  			/*
  			 * 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.
  			 */
  			break;
  		}
  
  		/*
  		 * 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;
  		if (!bfq_update_next_in_service(sd, entity, expiration) &&
  		    !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
   * a subtree with at least one eligible (start <= vtime) entity. The path on
   * 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.
   * @expiration: true if we are on the expiration path of the in-service queue
   *
   * This function is invoked when there has been a change in the trees
   * for sd, and we need to know what is the new next entity to serve
   * after this change.
   */
  static struct bfq_entity *bfq_lookup_next_entity(struct bfq_sched_data *sd,
  						 bool expiration)
  {
  	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++) {
  		/*
  		 * 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.
  		 */
  		entity = __bfq_lookup_next_entity(st + class_idx,
  						  sd->in_service_entity &&
  						  !expiration);
  
  		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;
  
  		/*
  		 * Reset the accumulator of the amount of service that
  		 * the entity is about to receive.
  		 */
  		entity->service = 0;
  
  		/*
  		 * If entity is no longer a candidate for next
  		 * 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.
  		 */
  		if (bfq_no_longer_next_in_service(entity))
  			bfq_active_extract(bfq_entity_service_tree(entity),
  					   entity);
  
  		/*
  		 * 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.
  		 *
  		 * 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.
  		 */
  	}
  
  	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;
  
  		if (!bfq_update_next_in_service(sd, NULL, false))
  			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),
  				    false, false);
  	bfq_clear_bfqq_non_blocking_wait_rq(bfqq);
  }
  
  void bfq_requeue_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
  		      bool expiration)
  {
  	struct bfq_entity *entity = &bfqq->entity;
  
  	bfq_activate_requeue_entity(entity, false,
  				    bfqq == bfqd->in_service_queue, expiration);
  }
  
  /*
   * 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)
  		bfq_weights_tree_remove(bfqd, &bfqq->entity,
  					&bfqd->queue_weights_tree);
  
  	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)
  			bfq_weights_tree_add(bfqd, &bfqq->entity,
  					     &bfqd->queue_weights_tree);
  
  	if (bfqq->wr_coeff > 1)
  		bfqd->wr_busy_queues++;
  }
  