// 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; return parent_sched_may_change; } #ifdef CONFIG_BFQ_GROUP_IOSCHED /* * 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; } static void bfq_inc_active_entities(struct bfq_entity *entity) { struct bfq_sched_data *sd = entity->sched_data; struct bfq_group *bfqg = container_of(sd, struct bfq_group, sched_data); if (bfqg != bfqg->bfqd->root_group) bfqg->active_entities++; } static void bfq_dec_active_entities(struct bfq_entity *entity) { struct bfq_sched_data *sd = entity->sched_data; struct bfq_group *bfqg = container_of(sd, struct bfq_group, sched_data); if (bfqg != bfqg->bfqd->root_group) bfqg->active_entities--; } #else /* CONFIG_BFQ_GROUP_IOSCHED */ 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; } static void bfq_inc_active_entities(struct bfq_entity *entity) { } static void bfq_dec_active_entities(struct bfq_entity *entity) { } #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) { return div64_ul((u64)service << WFQ_SERVICE_SHIFT, weight); } /** * 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; 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); if (bfqq) list_add(&bfqq->bfqq_list, &bfqq->bfqd->active_list[bfqq->actuator_idx]); bfq_inc_active_entities(entity); } /** * 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_NR_LEVELS - 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_NR_LEVELS * BFQ_WEIGHT_CONVERSION_COEFF. */ static unsigned short bfq_weight_to_ioprio(int weight) { return max_t(int, 0, IOPRIO_NR_LEVELS - weight / BFQ_WEIGHT_CONVERSION_COEFF); } 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; node = bfq_find_deepest(&entity->rb_node); bfq_extract(&st->active, entity); if (node) bfq_update_active_tree(node); if (bfqq) list_del(&bfqq->bfqq_list); bfq_dec_active_entities(entity); } /** * 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_or_in_serv = 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; /* 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) bfq_weights_tree_remove(bfqq); 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) bfq_weights_tree_add(bfqq); 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_or_in_serv = true; } bfq_update_fin_time_enqueue(entity, st, backshifted); } /** * __bfq_requeue_entity - handle requeueing or repositioning of an entity. * @entity: the entity being requeued or repositioned. * * Requeueing is needed if this entity stops being served, which * happens if a leaf descendant entity has expired. On the other hand, * repositioning is needed if the next_inservice_entity for the child * entity has changed. See the comments inside the function for * details. * * Basically, this function: 1) removes entity from its active tree if * present there, 2) updates the timestamps of entity and 3) inserts * entity back into its active tree (in the new, right position for * the new values of the timestamps). */ static void __bfq_requeue_entity(struct bfq_entity *entity) { struct bfq_sched_data *sd = entity->sched_data; struct bfq_service_tree *st = bfq_entity_service_tree(entity); if (entity == sd->in_service_entity) { /* * We are requeueing the current in-service entity, * which may have to be done for one of the following * reasons: * - entity represents the in-service queue, and the * in-service queue is being requeued after an * expiration; * - entity represents a group, and its budget has * changed because one of its child entities has * just been either activated or requeued for some * reason; the timestamps of the entity need then to * be updated, and the entity needs to be enqueued * or repositioned accordingly. * * In particular, before requeueing, the start time of * the entity must be moved forward to account for the * service that the entity has received while in * service. This is done by the next instructions. The * finish time will then be updated according to this * new value of the start time, and to the budget of * the entity. */ bfq_calc_finish(entity, entity->service); entity->start = entity->finish; /* * In addition, if the entity had more than one child * when set in service, then it was not extracted from * the active tree. This implies that the position of * the entity in the active tree may need to be * changed now, because we have just updated the start * time of the entity, and we will update its finish * time in a moment (the requeueing is then, more * precisely, a repositioning in this case). To * implement this repositioning, we: 1) dequeue the * entity here, 2) update the finish time and requeue * the entity according to the new timestamps below. */ if (entity->tree) bfq_active_extract(st, entity); } else { /* The entity is already active, and not in service */ /* * In this case, this function gets called only if the * next_in_service entity below this entity has * changed, and this change has caused the budget of * this entity to change, which, finally implies that * the finish time of this entity must be * updated. Such an update may cause the scheduling, * i.e., the position in the active tree, of this * entity to change. We handle this change by: 1) * dequeueing the entity here, 2) updating the finish * time and requeueing the entity according to the new * timestamps below. This is the same approach as the * non-extracted-entity sub-case above. */ bfq_active_extract(st, entity); } bfq_update_fin_time_enqueue(entity, st, false); } static void __bfq_activate_requeue_entity(struct bfq_entity *entity, bool non_blocking_wait_rq) { struct bfq_service_tree *st = bfq_entity_service_tree(entity); if (entity->sched_data->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) { for_each_entity(entity) { __bfq_activate_requeue_entity(entity, non_blocking_wait_rq); if (!bfq_update_next_in_service(entity->sched_data, 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_or_in_serv) /* * 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. * @in_service: whether or not there is an in-service entity for the sched_data * this active tree belongs to. * * 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; } 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_or_in_serv) { /* * 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); } void bfq_add_bfqq_in_groups_with_pending_reqs(struct bfq_queue *bfqq) { #ifdef CONFIG_BFQ_GROUP_IOSCHED struct bfq_entity *entity = &bfqq->entity; if (!entity->in_groups_with_pending_reqs) { entity->in_groups_with_pending_reqs = true; if (!(bfqq_group(bfqq)->num_queues_with_pending_reqs++)) bfqq->bfqd->num_groups_with_pending_reqs++; } #endif } void bfq_del_bfqq_in_groups_with_pending_reqs(struct bfq_queue *bfqq) { #ifdef CONFIG_BFQ_GROUP_IOSCHED struct bfq_entity *entity = &bfqq->entity; if (entity->in_groups_with_pending_reqs) { entity->in_groups_with_pending_reqs = false; if (!(--bfqq_group(bfqq)->num_queues_with_pending_reqs)) bfqq->bfqd->num_groups_with_pending_reqs--; } #endif } /* * 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_queue *bfqq, bool expiration) { struct bfq_data *bfqd = bfqq->bfqd; 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_del_bfqq_in_groups_with_pending_reqs(bfqq); /* * Next function is invoked last, because it causes bfqq to be * freed. DO NOT use bfqq after the next function invocation. */ bfq_weights_tree_remove(bfqq); } } /* * Called when an inactive queue receives a new request. */ void bfq_add_bfqq_busy(struct bfq_queue *bfqq) { struct bfq_data *bfqd = bfqq->bfqd; 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) { bfq_add_bfqq_in_groups_with_pending_reqs(bfqq); if (bfqq->wr_coeff == 1) bfq_weights_tree_add(bfqq); } if (bfqq->wr_coeff > 1) bfqd->wr_busy_queues++; /* Move bfqq to the head of the woken list of its waker */ if (!hlist_unhashed(&bfqq->woken_list_node) && &bfqq->woken_list_node != bfqq->waker_bfqq->woken_list.first) { hlist_del_init(&bfqq->woken_list_node); hlist_add_head(&bfqq->woken_list_node, &bfqq->waker_bfqq->woken_list); } }
