// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * 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).
 */
#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;
}

unsigned int bfq_tot_busy_queues(struct bfq_data *bfqd)
{
        return bfqd->busy_queues[0] + bfqd->busy_queues[1] +
                bfqd->busy_queues[2];
}

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 repositioning 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 repositioning 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) {
                bool new_budget_triggers_change =
                        bfq_update_parent_budget(next_in_service);

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

        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
        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;
}

/*
 * 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_cached *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

                /* Matches the smp_wmb() in bfq_group_set_weight. */
                smp_rmb();
                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, and the entity is a
                 * queue, remove the entity from its old weight counter (if
                 * there is a counter associated with the entity).
                 */
                if (prev_weight != new_weight && bfqq) {
                        root = &bfqd->queue_weights_tree;
                        __bfq_weights_tree_remove(bfqd, bfqq, root);
                }
                entity->weight = new_weight;
                /*
                 * Add the entity, if it is not a weight-raised queue,
                 * to the counter associated with its new weight.
                 */
                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);
                }

                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;
        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);

        /* 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, after 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;
        }

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

                if (!entity->in_groups_with_pending_reqs) {
                        entity->in_groups_with_pending_reqs = true;
                        bfqd->num_groups_with_pending_reqs++;
                }
        }
#endif

        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 - update sched_data and service trees for
 * entity, so as to represent entity as inactive
 * @entity: the entity being deactivated.
 * @ins_into_idle_tree: if false, the entity will not be put into the
 *                      idle tree.
 *
 * If necessary and allowed, puts entity into the idle tree. NOTE:
 * entity may be on no tree if in service.
 */
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;

        bfq_calc_finish(entity, entity->service);

        if (is_in_service)
                sd->in_service_entity = NULL;
        else
                /*
                 * Non in-service entity: nobody will take care of
                 * resetting its service counter on expiration. Do it
                 * now.
                 */
                entity->service = 0;

        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 contrast, 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_entity 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_entity 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 (bfq_tot_busy_queues(bfqd) == 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
                 * 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;
}

/* returns true if the in-service queue gets freed */
bool __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) {
                /*
                 * If no process is referencing in_serv_bfqq any
                 * longer, then the service reference may be the only
                 * reference to the queue. If this is the case, then
                 * bfqq gets freed here.
                 */
                int ref = in_serv_bfqq->ref;
                bfq_put_queue(in_serv_bfqq);
                if (ref == 1)
                        return true;
        }

        return false;
}

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[bfqq->ioprio_class - 1]--;

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

        bfqg_stats_update_dequeue(bfqq_group(bfqq));

        bfq_deactivate_bfqq(bfqd, bfqq, true, expiration);

        if (!bfqq->dispatched)
                bfq_weights_tree_remove(bfqd, bfqq);
}

/*
 * 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[bfqq->ioprio_class - 1]++;

        if (!bfqq->dispatched)
                if (bfqq->wr_coeff == 1)
                        bfq_weights_tree_add(bfqd, bfqq,
                                             &bfqd->queue_weights_tree);

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