Re: [PATCH] block: check more requests for multiple_queues in blk_attempt_plug_merge
From: Jens Axboe <axboe@kernel.dk>
Date: 2022-03-11 14:16:33
Also in:
linux-block, stable
Subsystem:
block layer, the rest · Maintainers:
Jens Axboe, Linus Torvalds
On 3/10/22 5:07 PM, Jens Axboe wrote:
In any case, just doing larger reads would likely help quite a bit, but would still be nice to get to the bottom of why we're not seeing the level of merging we expect.
Song, can you try this one? It'll do the dispatch in a somewhat saner fashion, bundling identical queues. And we'll keep iterating the plug list for a merge if we have multiple disks, until we've seen a queue match and checked.
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 0e871d4e7cb8..68b623d00db5 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c@@ -1073,12 +1073,20 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio, if (!plug || rq_list_empty(plug->mq_list)) return false; - /* check the previously added entry for a quick merge attempt */ - rq = rq_list_peek(&plug->mq_list); - if (rq->q == q) { - if (blk_attempt_bio_merge(q, rq, bio, nr_segs, false) == - BIO_MERGE_OK) - return true; + rq_list_for_each(&plug->mq_list, rq) { + if (rq->q == q) { + if (blk_attempt_bio_merge(q, rq, bio, nr_segs, false) == + BIO_MERGE_OK) + return true; + break; + } + + /* + * Only keep iterating plug list for merges if we have multiple + * queues + */ + if (!plug->multiple_queues) + break; } return false; }
diff --git a/block/blk-mq.c b/block/blk-mq.c
index bb263abbb40f..9c784262fd6b 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c@@ -2576,13 +2576,36 @@ static void __blk_mq_flush_plug_list(struct request_queue *q, q->mq_ops->queue_rqs(&plug->mq_list); } +static void blk_mq_dispatch_plug_list(struct blk_plug *plug, bool from_sched) +{ + struct blk_mq_hw_ctx *this_hctx = NULL; + struct blk_mq_ctx *this_ctx = NULL; + struct request *requeue_list = NULL; + unsigned int depth = 0; + LIST_HEAD(list); + + do { + struct request *rq = rq_list_pop(&plug->mq_list); + + if (!this_hctx) { + this_hctx = rq->mq_hctx; + this_ctx = rq->mq_ctx; + } else if (this_hctx != rq->mq_hctx || this_ctx != rq->mq_ctx) { + rq_list_add(&requeue_list, rq); + continue; + } + list_add_tail(&rq->queuelist, &list); + depth++; + } while (!rq_list_empty(plug->mq_list)); + + plug->mq_list = requeue_list; + trace_block_unplug(this_hctx->queue, depth, !from_sched); + blk_mq_sched_insert_requests(this_hctx, this_ctx, &list, from_sched); +} + void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule) { - struct blk_mq_hw_ctx *this_hctx; - struct blk_mq_ctx *this_ctx; struct request *rq; - unsigned int depth; - LIST_HEAD(list); if (rq_list_empty(plug->mq_list)) return;
@@ -2618,35 +2641,9 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule) return; } - this_hctx = NULL; - this_ctx = NULL; - depth = 0; do { - rq = rq_list_pop(&plug->mq_list); - - if (!this_hctx) { - this_hctx = rq->mq_hctx; - this_ctx = rq->mq_ctx; - } else if (this_hctx != rq->mq_hctx || this_ctx != rq->mq_ctx) { - trace_block_unplug(this_hctx->queue, depth, - !from_schedule); - blk_mq_sched_insert_requests(this_hctx, this_ctx, - &list, from_schedule); - depth = 0; - this_hctx = rq->mq_hctx; - this_ctx = rq->mq_ctx; - - } - - list_add(&rq->queuelist, &list); - depth++; + blk_mq_dispatch_plug_list(plug, from_schedule); } while (!rq_list_empty(plug->mq_list)); - - if (!list_empty(&list)) { - trace_block_unplug(this_hctx->queue, depth, !from_schedule); - blk_mq_sched_insert_requests(this_hctx, this_ctx, &list, - from_schedule); - } } void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
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Jens Axboe