Merge tag 'v3.3.7' into 3.3/master

[zen-stable.git] / block / bfq-sched.c

/*
 * BFQ: Hierarchical B-WF2Q+ scheduler.
 *
 * Based on ideas and code from CFQ:
 * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
 *
 * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
 *                    Paolo Valente <paolo.valente@unimore.it>
 */

#ifdef CONFIG_CGROUP_BFQIO
#define for_each_entity(entity) \
        for (; entity != NULL; entity = entity->parent)

#define for_each_entity_safe(entity, parent) \
        for (; entity && ({ parent = entity->parent; 1; }); entity = parent)

static struct bfq_entity *bfq_lookup_next_entity(struct bfq_sched_data *sd,
                                                 int extract,
                                                 struct bfq_data *bfqd);

static int bfq_update_next_active(struct bfq_sched_data *sd)
{
        struct bfq_group *bfqg;
        struct bfq_entity *entity, *next_active;

        if (sd->active_entity != NULL)
                /* will update/requeue at the end of service */
                return 0;

        /*
         * NOTE: this can be improved in many ways, such as returning
         * 1 (and thus propagating upwards the update) only when the
         * budget changes, or caching the bfqq that will be scheduled
         * next from this subtree.  By now we worry more about
         * correctness than about performance...
         */
        next_active = bfq_lookup_next_entity(sd, 0, NULL);
        sd->next_active = next_active;

        if (next_active != NULL) {
                bfqg = container_of(sd, struct bfq_group, sched_data);
                entity = bfqg->my_entity;
                if (entity != NULL)
                        entity->budget = next_active->budget;
        }

        return 1;
}

static inline void bfq_check_next_active(struct bfq_sched_data *sd,
                                         struct bfq_entity *entity)
{
        BUG_ON(sd->next_active != entity);
}
#else
#define for_each_entity(entity) \
        for (; entity != NULL; entity = NULL)

#define for_each_entity_safe(entity, parent) \
        for (parent = NULL; entity != NULL; entity = parent)

static inline int bfq_update_next_active(struct bfq_sched_data *sd)
{
        return 0;
}

static inline void bfq_check_next_active(struct bfq_sched_data *sd,
                                         struct bfq_entity *entity)
{
}
#endif

/*
 * 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

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

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

        BUG_ON(entity == NULL);

        if (entity->my_sched_data == NULL)
                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 inline 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 inline void bfq_calc_finish(struct bfq_entity *entity,
                                   unsigned long service)
{
        struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);

        BUG_ON(entity->weight == 0);

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

        if (bfqq != NULL) {
                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.
 */
static inline struct bfq_entity *bfq_entity_of(struct rb_node *node)
{
        struct bfq_entity *entity = NULL;

        if (node != NULL)
                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 inline void bfq_extract(struct rb_root *root,
                               struct bfq_entity *entity)
{
        BUG_ON(entity->tree != root);

        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;

        BUG_ON(entity->tree != &st->idle);

        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 != NULL)
                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;

        BUG_ON(entity->tree != NULL);

        while (*node != NULL) {
                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 inline void bfq_update_min(struct bfq_entity *entity,
                                  struct rb_node *node)
{
        struct bfq_entity *child;

        if (node != NULL) {
                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 inline 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 == NULL)
                return;

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

        bfq_insert(&st->active, entity);

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

        bfq_update_active_tree(node);

        if (bfqq != NULL)
                list_add(&bfqq->bfqq_list, &bfqq->bfqd->active_list);
}

/**
 * bfq_ioprio_to_weight - calc a weight from an ioprio.
 * @ioprio: the ioprio value to convert.
 */
static unsigned short bfq_ioprio_to_weight(int ioprio)
{
        WARN_ON(ioprio < 0 || ioprio >= IOPRIO_BE_NR);
        return IOPRIO_BE_NR - ioprio;
}

/**
 * bfq_weight_to_ioprio - calc an ioprio from a weight.
 * @weight: the weight value to convert.
 *
 * To preserve as mush 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
 */
static unsigned short bfq_weight_to_ioprio(int weight)
{
        WARN_ON(weight < BFQ_MIN_WEIGHT || weight > BFQ_MAX_WEIGHT);
        return IOPRIO_BE_NR - weight < 0 ? 0 : IOPRIO_BE_NR - weight;
}

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

        if (bfqq != NULL) {
                sd = entity->sched_data;
                atomic_inc(&bfqq->ref);
                bfq_log_bfqq(bfqq->bfqd, bfqq, "get_entity: %p %d",
                             bfqq, atomic_read(&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 == NULL && node->rb_left == NULL)
                deepest = rb_parent(node);
        else if (node->rb_right == NULL)
                deepest = node->rb_left;
        else if (node->rb_left == NULL)
                deepest = node->rb_right;
        else {
                deepest = rb_next(node);
                if (deepest->rb_right != NULL)
                        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;

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

        if (node != NULL)
                bfq_update_active_tree(node);

        if (bfqq != NULL)
                list_del(&bfqq->bfqq_list);
}

/**
 * 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 == NULL || bfq_gt(first_idle->finish, entity->finish))
                st->first_idle = entity;
        if (last_idle == NULL || bfq_gt(entity->finish, last_idle->finish))
                st->last_idle = entity;

        bfq_insert(&st->idle, entity);

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

/**
 * bfq_forget_entity - remove an entity from the wfq trees.
 * @st: the service tree.
 * @entity: the entity being removed.
 *
 * Update the device status and forget everything about @entity, putting
 * the device reference to it, if it is a queue.  Entities belonging to
 * groups are not refcounted.
 */
static void bfq_forget_entity(struct bfq_service_tree *st,
                              struct bfq_entity *entity)
{
        struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
        struct bfq_sched_data *sd;

        BUG_ON(!entity->on_st);

        entity->on_st = 0;
        st->wsum -= entity->weight;
        if (bfqq != NULL) {
                sd = entity->sched_data;
                bfq_log_bfqq(bfqq->bfqd, bfqq, "forget_entity: %p %d",
                             bfqq, atomic_read(&bfqq->ref));
                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.
 */
static void bfq_put_idle_entity(struct bfq_service_tree *st,
                                struct bfq_entity *entity)
{
        bfq_idle_extract(st, entity);
        bfq_forget_entity(st, 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 != NULL &&
            !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 != NULL && !bfq_gt(first_idle->finish, st->vtime))
                bfq_put_idle_entity(st, first_idle);
}

static struct bfq_service_tree *
__bfq_entity_update_weight_prio(struct bfq_service_tree *old_st,
                         struct bfq_entity *entity)
{
        struct bfq_service_tree *new_st = old_st;

        if (entity->ioprio_changed) {
                struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);

                BUG_ON(old_st->wsum < entity->weight);
                old_st->wsum -= entity->weight;

                if (entity->new_weight != entity->orig_weight) {
                        entity->orig_weight = entity->new_weight;
                        entity->ioprio =
                                bfq_weight_to_ioprio(entity->orig_weight);
                } else if (entity->new_ioprio != entity->ioprio) {
                        entity->ioprio = entity->new_ioprio;
                        entity->orig_weight =
                                        bfq_ioprio_to_weight(entity->ioprio);
                } else
                        entity->new_weight = entity->orig_weight =
                                bfq_ioprio_to_weight(entity->ioprio);

                entity->ioprio_class = entity->new_ioprio_class;
                entity->ioprio_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);
                entity->weight = entity->orig_weight *
                        (bfqq != NULL ? bfqq->raising_coeff : 1);
                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.
 */
static void bfq_bfqq_served(struct bfq_queue *bfqq, unsigned long served)
{
        struct bfq_entity *entity = &bfqq->entity;
        struct bfq_service_tree *st;

        for_each_entity(entity) {
                st = bfq_entity_service_tree(entity);

                entity->service += served;
                WARN_ON_ONCE(entity->service > entity->budget);
                BUG_ON(st->wsum == 0);

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

/**
 * bfq_bfqq_charge_full_budget - set the service to the entity budget.
 * @bfqq: the queue that needs a service update.
 *
 * When it's not possible to be fair in the service domain, because
 * a queue is not consuming its budget fast enough (the meaning of
 * fast depends on the timeout parameter), we charge it a full
 * budget.  In this way we should obtain a sort of time-domain
 * fairness among all the seeky/slow queues.
 */
static inline void bfq_bfqq_charge_full_budget(struct bfq_queue *bfqq)
{
        struct bfq_entity *entity = &bfqq->entity;

        bfq_log_bfqq(bfqq->bfqd, bfqq, "charge_full_budget");

        bfq_bfqq_served(bfqq, entity->budget - entity->service);
}

/**
 * __bfq_activate_entity - activate an entity.
 * @entity: the entity being activated.
 *
 * Called whenever an entity is activated, i.e., it is not active and one
 * of its children receives a new request, or has to be reactivated due to
 * budget exhaustion.  It uses the current budget of the entity (and the
 * service received if @entity is active) of the queue to calculate its
 * timestamps.
 */
static void __bfq_activate_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->active_entity) {
                BUG_ON(entity->tree != NULL);
                /*
                 * If we are requeueing the current entity we have
                 * to take care of not charging to it service it has
                 * not received.
                 */
                bfq_calc_finish(entity, entity->service);
                entity->start = entity->finish;
                sd->active_entity = NULL;
        } else if (entity->tree == &st->active) {
                /*
                 * Requeueing an entity due to a change of some
                 * next_active entity below it.  We reuse the old
                 * start time.
                 */
                bfq_active_extract(st, entity);
        } else if (entity->tree == &st->idle) {
                /*
                 * Must be on the idle tree, bfq_idle_extract() will
                 * check for that.
                 */
                bfq_idle_extract(st, entity);
                entity->start = bfq_gt(st->vtime, entity->finish) ?
                                       st->vtime : entity->finish;
        } else {
                /*
                 * The finish time of the entity may be invalid, and
                 * it is in the past for sure, otherwise the queue
                 * would have been on the idle tree.
                 */
                entity->start = st->vtime;
                st->wsum += entity->weight;
                bfq_get_entity(entity);

                BUG_ON(entity->on_st);
                entity->on_st = 1;
        }

        st = __bfq_entity_update_weight_prio(st, entity);
        bfq_calc_finish(entity, entity->budget);
        bfq_active_insert(st, entity);
}

/**
 * bfq_activate_entity - activate an entity and its ancestors if necessary.
 * @entity: the entity to activate.
 *
 * Activate @entity and all the entities on the path from it to the root.
 */
static void bfq_activate_entity(struct bfq_entity *entity)
{
        struct bfq_sched_data *sd;

        for_each_entity(entity) {
                __bfq_activate_entity(entity);

                sd = entity->sched_data;
                if (!bfq_update_next_active(sd))
                        /*
                         * No need to propagate the activation to the
                         * upper entities, as they will be updated when
                         * the active entity is rescheduled.
                         */
                        break;
        }
}

/**
 * __bfq_deactivate_entity - deactivate an entity from its service tree.
 * @entity: the entity to deactivate.
 * @requeue: if false, the entity will not be put into the idle tree.
 *
 * Deactivate an entity, independently from its previous state.  If the
 * entity was not on a service tree just return, otherwise if it is on
 * any scheduler tree, extract it from that tree, and if necessary
 * and if the caller did not specify @requeue, put it on the idle tree.
 *
 * Return %1 if the caller should update the entity hierarchy, i.e.,
 * if the entity was under service or if it was the next_active for
 * its sched_data; return %0 otherwise.
 */
static int __bfq_deactivate_entity(struct bfq_entity *entity, int requeue)
{
        struct bfq_sched_data *sd = entity->sched_data;
        struct bfq_service_tree *st = bfq_entity_service_tree(entity);
        int was_active = entity == sd->active_entity;
        int ret = 0;

        if (!entity->on_st)
                return 0;

        BUG_ON(was_active && entity->tree != NULL);

        if (was_active) {
                bfq_calc_finish(entity, entity->service);
                sd->active_entity = NULL;
        } else if (entity->tree == &st->active)
                bfq_active_extract(st, entity);
        else if (entity->tree == &st->idle)
                bfq_idle_extract(st, entity);
        else if (entity->tree != NULL)
                BUG();

        if (was_active || sd->next_active == entity)
                ret = bfq_update_next_active(sd);

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

        BUG_ON(sd->active_entity == entity);
        BUG_ON(sd->next_active == entity);

        return ret;
}

/**
 * bfq_deactivate_entity - deactivate an entity.
 * @entity: the entity to deactivate.
 * @requeue: true if the entity can be put on the idle tree
 */
static void bfq_deactivate_entity(struct bfq_entity *entity, int requeue)
{
        struct bfq_sched_data *sd;
        struct bfq_entity *parent;

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

                if (!__bfq_deactivate_entity(entity, requeue))
                        /*
                         * The parent entity is still backlogged, and
                         * we don't need to update it as it is still
                         * under service.
                         */
                        break;

                if (sd->next_active != NULL)
                        /*
                         * The parent entity is still backlogged and
                         * the budgets on the path towards the root
                         * need to be updated.
                         */
                        goto update;

                /*
                 * If we reach there the parent is no more backlogged and
                 * we want to propagate the dequeue upwards.
                 */
                requeue = 1;
        }

        return;

update:
        entity = parent;
        for_each_entity(entity) {
                __bfq_activate_entity(entity);

                sd = entity->sched_data;
                if (!bfq_update_next_active(sd))
                        break;
        }
}

/**
 * bfq_update_vtime - update vtime if necessary.
 * @st: the service tree to act upon.
 *
 * If necessary update the service tree vtime to have at least one
 * eligible entity, skipping to its start time.  Assumes that the
 * active tree of the device is not empty.
 *
 * NOTE: this hierarchical implementation updates vtimes quite often,
 * we may end up with reactivated tasks getting timestamps after a
 * vtime skip done because we needed a ->first_active entity on some
 * intermediate node.
 */
static void bfq_update_vtime(struct bfq_service_tree *st)
{
        struct bfq_entity *entry;
        struct rb_node *node = st->active.rb_node;

        entry = rb_entry(node, struct bfq_entity, rb_node);
        if (bfq_gt(entry->min_start, st->vtime)) {
                st->vtime = entry->min_start;
                bfq_forget_idle(st);
        }
}

/**
 * bfq_first_active - find the eligible entity with the smallest finish time
 * @st: the service tree to select from.
 *
 * 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)
{
        struct bfq_entity *entry, *first = NULL;
        struct rb_node *node = st->active.rb_node;

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

                BUG_ON(bfq_gt(entry->min_start, st->vtime));

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

        BUG_ON(first == NULL && !RB_EMPTY_ROOT(&st->active));
        return first;
}

/**
 * __bfq_lookup_next_entity - return the first eligible entity in @st.
 * @st: the service tree.
 *
 * Update the virtual time in @st and return the first eligible entity
 * it contains.
 */
static struct bfq_entity *__bfq_lookup_next_entity(struct bfq_service_tree *st)
{
        struct bfq_entity *entity;

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

        bfq_update_vtime(st);
        entity = bfq_first_active_entity(st);
        BUG_ON(bfq_gt(entity->start, st->vtime));

        return entity;
}

/**
 * bfq_lookup_next_entity - return the first eligible entity in @sd.
 * @sd: the sched_data.
 * @extract: if true the returned entity will be also extracted from @sd.
 *
 * NOTE: since we cache the next_active entity at each level of the
 * hierarchy, the complexity of the lookup can be decreased with
 * absolutely no effort just returning the cached next_active value;
 * we prefer to do full lookups to test the consistency of * the data
 * structures.
 */
static struct bfq_entity *bfq_lookup_next_entity(struct bfq_sched_data *sd,
                                                 int extract,
                                                 struct bfq_data *bfqd)
{
        struct bfq_service_tree *st = sd->service_tree;
        struct bfq_entity *entity;
        int i=0;

        BUG_ON(sd->active_entity != NULL);

        if (bfqd != NULL &&
            jiffies - bfqd->bfq_class_idle_last_service > BFQ_CL_IDLE_TIMEOUT) {
                entity = __bfq_lookup_next_entity(st + BFQ_IOPRIO_CLASSES - 1);
                if (entity != NULL) {
                        i = BFQ_IOPRIO_CLASSES - 1;
                        bfqd->bfq_class_idle_last_service = jiffies;
                        sd->next_active = entity;
                }
        }
        for (; i < BFQ_IOPRIO_CLASSES; i++) {
                entity = __bfq_lookup_next_entity(st + i);
                if (entity != NULL) {
                        if (extract) {
                                bfq_check_next_active(sd, entity);
                                bfq_active_extract(st + i, entity);
                                sd->active_entity = entity;
                                sd->next_active = NULL;
                        }
                        break;
                }
        }

        return entity;
}

/*
 * Get next queue for service.
 */
static 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;

        BUG_ON(bfqd->active_queue != NULL);

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

        sd = &bfqd->root_group->sched_data;
        for (; sd != NULL; sd = entity->my_sched_data) {
                entity = bfq_lookup_next_entity(sd, 1, bfqd);
                BUG_ON(entity == NULL);
                entity->service = 0;
        }

        bfqq = bfq_entity_to_bfqq(entity);
        BUG_ON(bfqq == NULL);

        return bfqq;
}

/*
 * Forced extraction of the given queue.
 */
static void bfq_get_next_queue_forced(struct bfq_data *bfqd,
                                      struct bfq_queue *bfqq)
{
        struct bfq_entity *entity;
        struct bfq_sched_data *sd;

        BUG_ON(bfqd->active_queue != NULL);

        entity = &bfqq->entity;
        /*
         * Bubble up extraction/update from the leaf to the root.
        */
        for_each_entity(entity) {
                sd = entity->sched_data;
                bfq_update_vtime(bfq_entity_service_tree(entity));
                bfq_active_extract(bfq_entity_service_tree(entity), entity);
                sd->active_entity = entity;
                sd->next_active = NULL;
                entity->service = 0;
        }

        return;
}

static void __bfq_bfqd_reset_active(struct bfq_data *bfqd)
{
        if (bfqd->active_bic != NULL) {
                put_io_context(bfqd->active_bic->icq.ioc);
                bfqd->active_bic = NULL;
        }

        bfqd->active_queue = NULL;
        del_timer(&bfqd->idle_slice_timer);
}

static void bfq_deactivate_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
                                int requeue)
{
        struct bfq_entity *entity = &bfqq->entity;

        if (bfqq == bfqd->active_queue)
                __bfq_bfqd_reset_active(bfqd);

        bfq_deactivate_entity(entity, requeue);
}

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

        bfq_activate_entity(entity);
}

/*
 * Called when the bfqq no longer has requests pending, remove it from
 * the service tree.
 */
static void bfq_del_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq,
                              int requeue)
{
        BUG_ON(!bfq_bfqq_busy(bfqq));
        BUG_ON(!RB_EMPTY_ROOT(&bfqq->sort_list));

        bfq_log_bfqq(bfqd, bfqq, "del from busy");

        bfq_clear_bfqq_busy(bfqq);

        BUG_ON(bfqd->busy_queues == 0);
        bfqd->busy_queues--;

        bfq_deactivate_bfqq(bfqd, bfqq, requeue);
}

/*
 * Called when an inactive queue receives a new request.
 */
static void bfq_add_bfqq_busy(struct bfq_data *bfqd, struct bfq_queue *bfqq)
{
        BUG_ON(bfq_bfqq_busy(bfqq));
        BUG_ON(bfqq == bfqd->active_queue);

        bfq_log_bfqq(bfqd, bfqq, "add to busy");

        bfq_activate_bfqq(bfqd, bfqq);

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