diff options
| -rw-r--r-- | block/bfq-cgroup.c | 3 | ||||
| -rw-r--r-- | block/bfq-iosched.c | 73 | ||||
| -rw-r--r-- | block/bfq-iosched.h | 3 |
3 files changed, 73 insertions, 6 deletions
diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c index c6113af31960..2a74a3f2a8f7 100644 --- a/block/bfq-cgroup.c +++ b/block/bfq-cgroup.c @@ -578,7 +578,8 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq, bfqg_and_blkg_get(bfqg); if (bfq_bfqq_busy(bfqq)) { - bfq_pos_tree_add_move(bfqd, bfqq); + if (unlikely(!bfqd->nonrot_with_queueing)) + bfq_pos_tree_add_move(bfqd, bfqq); bfq_activate_bfqq(bfqd, bfqq); } diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index f59efee7a601..b957e9db87d8 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -595,7 +595,16 @@ static bool bfq_too_late_for_merging(struct bfq_queue *bfqq) bfq_merge_time_limit); } -void bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq) +/* + * The following function is not marked as __cold because it is + * actually cold, but for the same performance goal described in the + * comments on the likely() at the beginning of + * bfq_setup_cooperator(). Unexpectedly, to reach an even lower + * execution time for the case where this function is not invoked, we + * had to add an unlikely() in each involved if(). + */ +void __cold +bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq) { struct rb_node **p, *parent; struct bfq_queue *__bfqq; @@ -1849,8 +1858,9 @@ static void bfq_add_request(struct request *rq) /* * Adjust priority tree position, if next_rq changes. + * See comments on bfq_pos_tree_add_move() for the unlikely(). */ - if (prev != bfqq->next_rq) + if (unlikely(!bfqd->nonrot_with_queueing && prev != bfqq->next_rq)) bfq_pos_tree_add_move(bfqd, bfqq); if (!bfq_bfqq_busy(bfqq)) /* switching to busy ... */ @@ -1990,7 +2000,9 @@ static void bfq_remove_request(struct request_queue *q, bfqq->pos_root = NULL; } } else { - bfq_pos_tree_add_move(bfqd, bfqq); + /* see comments on bfq_pos_tree_add_move() for the unlikely() */ + if (unlikely(!bfqd->nonrot_with_queueing)) + bfq_pos_tree_add_move(bfqd, bfqq); } if (rq->cmd_flags & REQ_META) @@ -2075,7 +2087,12 @@ static void bfq_request_merged(struct request_queue *q, struct request *req, */ if (prev != bfqq->next_rq) { bfq_updated_next_req(bfqd, bfqq); - bfq_pos_tree_add_move(bfqd, bfqq); + /* + * See comments on bfq_pos_tree_add_move() for + * the unlikely(). + */ + if (unlikely(!bfqd->nonrot_with_queueing)) + bfq_pos_tree_add_move(bfqd, bfqq); } } } @@ -2358,6 +2375,46 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, struct bfq_queue *in_service_bfqq, *new_bfqq; /* + * Do not perform queue merging if the device is non + * rotational and performs internal queueing. In fact, such a + * device reaches a high speed through internal parallelism + * and pipelining. This means that, to reach a high + * throughput, it must have many requests enqueued at the same + * time. But, in this configuration, the internal scheduling + * algorithm of the device does exactly the job of queue + * merging: it reorders requests so as to obtain as much as + * possible a sequential I/O pattern. As a consequence, with + * the workload generated by processes doing interleaved I/O, + * the throughput reached by the device is likely to be the + * same, with and without queue merging. + * + * Disabling merging also provides a remarkable benefit in + * terms of throughput. Merging tends to make many workloads + * artificially more uneven, because of shared queues + * remaining non empty for incomparably more time than + * non-merged queues. This may accentuate workload + * asymmetries. For example, if one of the queues in a set of + * merged queues has a higher weight than a normal queue, then + * the shared queue may inherit such a high weight and, by + * staying almost always active, may force BFQ to perform I/O + * plugging most of the time. This evidently makes it harder + * for BFQ to let the device reach a high throughput. + * + * Finally, the likely() macro below is not used because one + * of the two branches is more likely than the other, but to + * have the code path after the following if() executed as + * fast as possible for the case of a non rotational device + * with queueing. We want it because this is the fastest kind + * of device. On the opposite end, the likely() may lengthen + * the execution time of BFQ for the case of slower devices + * (rotational or at least without queueing). But in this case + * the execution time of BFQ matters very little, if not at + * all. + */ + if (likely(bfqd->nonrot_with_queueing)) + return NULL; + + /* * Prevent bfqq from being merged if it has been created too * long ago. The idea is that true cooperating processes, and * thus their associated bfq_queues, are supposed to be @@ -2986,8 +3043,10 @@ static void __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq) bfq_requeue_bfqq(bfqd, bfqq, true); /* * Resort priority tree of potential close cooperators. + * See comments on bfq_pos_tree_add_move() for the unlikely(). */ - bfq_pos_tree_add_move(bfqd, bfqq); + if (unlikely(!bfqd->nonrot_with_queueing)) + bfq_pos_tree_add_move(bfqd, bfqq); } /* @@ -5051,6 +5110,9 @@ static void bfq_update_hw_tag(struct bfq_data *bfqd) bfqd->hw_tag = bfqd->max_rq_in_driver > BFQ_HW_QUEUE_THRESHOLD; bfqd->max_rq_in_driver = 0; bfqd->hw_tag_samples = 0; + + bfqd->nonrot_with_queueing = + blk_queue_nonrot(bfqd->queue) && bfqd->hw_tag; } static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd) @@ -5882,6 +5944,7 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e) INIT_HLIST_HEAD(&bfqd->burst_list); bfqd->hw_tag = -1; + bfqd->nonrot_with_queueing = blk_queue_nonrot(bfqd->queue); bfqd->bfq_max_budget = bfq_default_max_budget; diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h index 26869cfbbfa9..829730b96fb2 100644 --- a/block/bfq-iosched.h +++ b/block/bfq-iosched.h @@ -497,6 +497,9 @@ struct bfq_data { /* number of requests dispatched and waiting for completion */ int rq_in_driver; + /* true if the device is non rotational and performs queueing */ + bool nonrot_with_queueing; + /* * Maximum number of requests in driver in the last * @hw_tag_samples completed requests. |