diff options
| -rw-r--r-- | block/bfq-iosched.c | 204 | ||||
| -rw-r--r-- | block/bfq-iosched.h | 6 | ||||
| -rw-r--r-- | block/bfq-wf2q.c | 2 |
3 files changed, 118 insertions, 94 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index f30d1cb887d4..2eb587fe7c1a 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -629,12 +629,19 @@ void bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq) } /* - * The following function returns true if every queue must receive the - * same share of the throughput (this condition is used when deciding - * whether idling may be disabled, see the comments in the function - * bfq_better_to_idle()). + * The following function returns false either if every active queue + * must receive the same share of the throughput (symmetric scenario), + * or, as a special case, if bfqq must receive a share of the + * throughput lower than or equal to the share that every other active + * queue must receive. If bfqq does sync I/O, then these are the only + * two cases where bfqq happens to be guaranteed its share of the + * throughput even if I/O dispatching is not plugged when bfqq remains + * temporarily empty (for more details, see the comments in the + * function bfq_better_to_idle()). For this reason, the return value + * of this function is used to check whether I/O-dispatch plugging can + * be avoided. * - * Such a scenario occurs when: + * The above first case (symmetric scenario) occurs when: * 1) all active queues have the same weight, * 2) all active queues belong to the same I/O-priority class, * 3) all active groups at the same level in the groups tree have the same @@ -654,30 +661,36 @@ void bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq) * support or the cgroups interface are not enabled, thus no state * needs to be maintained in this case. */ -static bool bfq_symmetric_scenario(struct bfq_data *bfqd) +static bool bfq_asymmetric_scenario(struct bfq_data *bfqd, + struct bfq_queue *bfqq) { + bool smallest_weight = bfqq && + bfqq->weight_counter && + bfqq->weight_counter == + container_of( + rb_first_cached(&bfqd->queue_weights_tree), + struct bfq_weight_counter, + weights_node); + /* * For queue weights to differ, queue_weights_tree must contain * at least two nodes. */ - bool varied_queue_weights = !RB_EMPTY_ROOT(&bfqd->queue_weights_tree) && - (bfqd->queue_weights_tree.rb_node->rb_left || - bfqd->queue_weights_tree.rb_node->rb_right); + bool varied_queue_weights = !smallest_weight && + !RB_EMPTY_ROOT(&bfqd->queue_weights_tree.rb_root) && + (bfqd->queue_weights_tree.rb_root.rb_node->rb_left || + bfqd->queue_weights_tree.rb_root.rb_node->rb_right); bool multiple_classes_busy = (bfqd->busy_queues[0] && bfqd->busy_queues[1]) || (bfqd->busy_queues[0] && bfqd->busy_queues[2]) || (bfqd->busy_queues[1] && bfqd->busy_queues[2]); - /* - * For queue weights to differ, queue_weights_tree must contain - * at least two nodes. - */ - return !(varied_queue_weights || multiple_classes_busy + return varied_queue_weights || multiple_classes_busy #ifdef CONFIG_BFQ_GROUP_IOSCHED || bfqd->num_groups_with_pending_reqs > 0 #endif - ); + ; } /* @@ -694,10 +707,11 @@ static bool bfq_symmetric_scenario(struct bfq_data *bfqd) * should be low too. */ void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq, - struct rb_root *root) + struct rb_root_cached *root) { struct bfq_entity *entity = &bfqq->entity; - struct rb_node **new = &(root->rb_node), *parent = NULL; + struct rb_node **new = &(root->rb_root.rb_node), *parent = NULL; + bool leftmost = true; /* * Do not insert if the queue is already associated with a @@ -726,8 +740,10 @@ void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq, } if (entity->weight < __counter->weight) new = &((*new)->rb_left); - else + else { new = &((*new)->rb_right); + leftmost = false; + } } bfqq->weight_counter = kzalloc(sizeof(struct bfq_weight_counter), @@ -736,7 +752,7 @@ void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq, /* * In the unlucky event of an allocation failure, we just * exit. This will cause the weight of queue to not be - * considered in bfq_symmetric_scenario, which, in its turn, + * considered in bfq_asymmetric_scenario, which, in its turn, * causes the scenario to be deemed wrongly symmetric in case * bfqq's weight would have been the only weight making the * scenario asymmetric. On the bright side, no unbalance will @@ -750,7 +766,8 @@ void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq, bfqq->weight_counter->weight = entity->weight; rb_link_node(&bfqq->weight_counter->weights_node, parent, new); - rb_insert_color(&bfqq->weight_counter->weights_node, root); + rb_insert_color_cached(&bfqq->weight_counter->weights_node, root, + leftmost); inc_counter: bfqq->weight_counter->num_active++; @@ -765,7 +782,7 @@ inc_counter: */ void __bfq_weights_tree_remove(struct bfq_data *bfqd, struct bfq_queue *bfqq, - struct rb_root *root) + struct rb_root_cached *root) { if (!bfqq->weight_counter) return; @@ -774,7 +791,7 @@ void __bfq_weights_tree_remove(struct bfq_data *bfqd, if (bfqq->weight_counter->num_active > 0) goto reset_entity_pointer; - rb_erase(&bfqq->weight_counter->weights_node, root); + rb_erase_cached(&bfqq->weight_counter->weights_node, root); kfree(bfqq->weight_counter); reset_entity_pointer: @@ -889,7 +906,7 @@ static unsigned long bfq_serv_to_charge(struct request *rq, struct bfq_queue *bfqq) { if (bfq_bfqq_sync(bfqq) || bfqq->wr_coeff > 1 || - !bfq_symmetric_scenario(bfqq->bfqd)) + bfq_asymmetric_scenario(bfqq->bfqd, bfqq)) return blk_rq_sectors(rq); return blk_rq_sectors(rq) * bfq_async_charge_factor; @@ -2543,7 +2560,7 @@ static void bfq_arm_slice_timer(struct bfq_data *bfqd) * queue). */ if (BFQQ_SEEKY(bfqq) && bfqq->wr_coeff == 1 && - bfq_symmetric_scenario(bfqd)) + !bfq_asymmetric_scenario(bfqd, bfqq)) sl = min_t(u64, sl, BFQ_MIN_TT); else if (bfqq->wr_coeff > 1) sl = max_t(u32, sl, 20ULL * NSEC_PER_MSEC); @@ -3500,8 +3517,9 @@ static bool idling_boosts_thr_without_issues(struct bfq_data *bfqd, } /* - * There is a case where idling must be performed not for - * throughput concerns, but to preserve service guarantees. + * There is a case where idling does not have to be performed for + * throughput concerns, but to preserve the throughput share of + * the process associated with bfqq. * * To introduce this case, we can note that allowing the drive * to enqueue more than one request at a time, and hence @@ -3517,77 +3535,83 @@ static bool idling_boosts_thr_without_issues(struct bfq_data *bfqd, * concern about per-process throughput distribution, and * makes its decisions only on a per-request basis. Therefore, * the service distribution enforced by the drive's internal - * scheduler is likely to coincide with the desired - * device-throughput distribution only in a completely - * symmetric scenario where: - * (i) each of these processes must get the same throughput as - * the others; - * (ii) the I/O of each process has the same properties, in - * terms of locality (sequential or random), direction - * (reads or writes), request sizes, greediness - * (from I/O-bound to sporadic), and so on. - * In fact, in such a scenario, the drive tends to treat - * the requests of each of these processes in about the same - * way as the requests of the others, and thus to provide - * each of these processes with about the same throughput - * (which is exactly the desired throughput distribution). In - * contrast, in any asymmetric scenario, device idling is - * certainly needed to guarantee that bfqq receives its - * assigned fraction of the device throughput (see [1] for - * details). - * The problem is that idling may significantly reduce - * throughput with certain combinations of types of I/O and - * devices. An important example is sync random I/O, on flash - * storage with command queueing. So, unless bfqq falls in the - * above cases where idling also boosts throughput, it would - * be important to check conditions (i) and (ii) accurately, - * so as to avoid idling when not strictly needed for service - * guarantees. + * scheduler is likely to coincide with the desired throughput + * distribution only in a completely symmetric, or favorably + * skewed scenario where: + * (i-a) each of these processes must get the same throughput as + * the others, + * (i-b) in case (i-a) does not hold, it holds that the process + * associated with bfqq must receive a lower or equal + * throughput than any of the other processes; + * (ii) the I/O of each process has the same properties, in + * terms of locality (sequential or random), direction + * (reads or writes), request sizes, greediness + * (from I/O-bound to sporadic), and so on; + + * In fact, in such a scenario, the drive tends to treat the requests + * of each process in about the same way as the requests of the + * others, and thus to provide each of these processes with about the + * same throughput. This is exactly the desired throughput + * distribution if (i-a) holds, or, if (i-b) holds instead, this is an + * even more convenient distribution for (the process associated with) + * bfqq. + * + * In contrast, in any asymmetric or unfavorable scenario, device + * idling (I/O-dispatch plugging) is certainly needed to guarantee + * that bfqq receives its assigned fraction of the device throughput + * (see [1] for details). + * + * The problem is that idling may significantly reduce throughput with + * certain combinations of types of I/O and devices. An important + * example is sync random I/O on flash storage with command + * queueing. So, unless bfqq falls in cases where idling also boosts + * throughput, it is important to check conditions (i-a), i(-b) and + * (ii) accurately, so as to avoid idling when not strictly needed for + * service guarantees. * - * Unfortunately, it is extremely difficult to thoroughly - * check condition (ii). And, in case there are active groups, - * it becomes very difficult to check condition (i) too. In - * fact, if there are active groups, then, for condition (i) - * to become false, it is enough that an active group contains - * more active processes or sub-groups than some other active - * group. More precisely, for condition (i) to hold because of - * such a group, it is not even necessary that the group is - * (still) active: it is sufficient that, even if the group - * has become inactive, some of its descendant processes still - * have some request already dispatched but still waiting for - * completion. In fact, requests have still to be guaranteed - * their share of the throughput even after being - * dispatched. In this respect, it is easy to show that, if a - * group frequently becomes inactive while still having - * in-flight requests, and if, when this happens, the group is - * not considered in the calculation of whether the scenario - * is asymmetric, then the group may fail to be guaranteed its - * fair share of the throughput (basically because idling may - * not be performed for the descendant processes of the group, - * but it had to be). We address this issue with the - * following bi-modal behavior, implemented in the function - * bfq_symmetric_scenario(). + * Unfortunately, it is extremely difficult to thoroughly check + * condition (ii). And, in case there are active groups, it becomes + * very difficult to check conditions (i-a) and (i-b) too. In fact, + * if there are active groups, then, for conditions (i-a) or (i-b) to + * become false 'indirectly', it is enough that an active group + * contains more active processes or sub-groups than some other active + * group. More precisely, for conditions (i-a) or (i-b) to become + * false because of such a group, it is not even necessary that the + * group is (still) active: it is sufficient that, even if the group + * has become inactive, some of its descendant processes still have + * some request already dispatched but still waiting for + * completion. In fact, requests have still to be guaranteed their + * share of the throughput even after being dispatched. In this + * respect, it is easy to show that, if a group frequently becomes + * inactive while still having in-flight requests, and if, when this + * happens, the group is not considered in the calculation of whether + * the scenario is asymmetric, then the group may fail to be + * guaranteed its fair share of the throughput (basically because + * idling may not be performed for the descendant processes of the + * group, but it had to be). We address this issue with the following + * bi-modal behavior, implemented in the function + * bfq_asymmetric_scenario(). * * If there are groups with requests waiting for completion * (as commented above, some of these groups may even be * already inactive), then the scenario is tagged as * asymmetric, conservatively, without checking any of the - * conditions (i) and (ii). So the device is idled for bfqq. + * conditions (i-a), (i-b) or (ii). So the device is idled for bfqq. * This behavior matches also the fact that groups are created * exactly if controlling I/O is a primary concern (to * preserve bandwidth and latency guarantees). * - * On the opposite end, if there are no groups with requests - * waiting for completion, then only condition (i) is actually - * controlled, i.e., provided that condition (i) holds, idling - * is not performed, regardless of whether condition (ii) - * holds. In other words, only if condition (i) does not hold, - * then idling is allowed, and the device tends to be - * prevented from queueing many requests, possibly of several - * processes. Since there are no groups with requests waiting - * for completion, then, to control condition (i) it is enough - * to check just whether all the queues with requests waiting - * for completion also have the same weight. + * On the opposite end, if there are no groups with requests waiting + * for completion, then only conditions (i-a) and (i-b) are actually + * controlled, i.e., provided that conditions (i-a) or (i-b) holds, + * idling is not performed, regardless of whether condition (ii) + * holds. In other words, only if conditions (i-a) and (i-b) do not + * hold, then idling is allowed, and the device tends to be prevented + * from queueing many requests, possibly of several processes. Since + * there are no groups with requests waiting for completion, then, to + * control conditions (i-a) and (i-b) it is enough to check just + * whether all the queues with requests waiting for completion also + * have the same weight. * * Not checking condition (ii) evidently exposes bfqq to the * risk of getting less throughput than its fair share. @@ -3639,7 +3663,7 @@ static bool idling_boosts_thr_without_issues(struct bfq_data *bfqd, * compound condition that is checked below for deciding * whether the scenario is asymmetric. To explain this * compound condition, we need to add that the function - * bfq_symmetric_scenario checks the weights of only + * bfq_asymmetric_scenario checks the weights of only * non-weight-raised queues, for efficiency reasons (see * comments on bfq_weights_tree_add()). Then the fact that * bfqq is weight-raised is checked explicitly here. More @@ -3667,7 +3691,7 @@ static bool idling_needed_for_service_guarantees(struct bfq_data *bfqd, return (bfqq->wr_coeff > 1 && bfqd->wr_busy_queues < bfq_tot_busy_queues(bfqd)) || - !bfq_symmetric_scenario(bfqd); + bfq_asymmetric_scenario(bfqd, bfqq); } /* @@ -5505,7 +5529,7 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e) HRTIMER_MODE_REL); bfqd->idle_slice_timer.function = bfq_idle_slice_timer; - bfqd->queue_weights_tree = RB_ROOT; + bfqd->queue_weights_tree = RB_ROOT_CACHED; bfqd->num_groups_with_pending_reqs = 0; INIT_LIST_HEAD(&bfqd->active_list); diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h index 062e1c4787f4..81cabf51a87e 100644 --- a/block/bfq-iosched.h +++ b/block/bfq-iosched.h @@ -450,7 +450,7 @@ struct bfq_data { * weight-raised @bfq_queue (see the comments to the functions * bfq_weights_tree_[add|remove] for further details). */ - struct rb_root queue_weights_tree; + struct rb_root_cached queue_weights_tree; /* * Number of groups with at least one descendant process that @@ -898,10 +898,10 @@ void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq, bool is_sync); struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic); void bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq); void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq, - struct rb_root *root); + struct rb_root_cached *root); void __bfq_weights_tree_remove(struct bfq_data *bfqd, struct bfq_queue *bfqq, - struct rb_root *root); + struct rb_root_cached *root); void bfq_weights_tree_remove(struct bfq_data *bfqd, struct bfq_queue *bfqq); void bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq, diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c index a11bef75483d..51ef1f00df80 100644 --- a/block/bfq-wf2q.c +++ b/block/bfq-wf2q.c @@ -737,7 +737,7 @@ __bfq_entity_update_weight_prio(struct bfq_service_tree *old_st, struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity); unsigned int prev_weight, new_weight; struct bfq_data *bfqd = NULL; - struct rb_root *root; + struct rb_root_cached *root; #ifdef CONFIG_BFQ_GROUP_IOSCHED struct bfq_sched_data *sd; struct bfq_group *bfqg; |