From 95ed0c5b1292fb90fe100af88541a7bef6ba44ec Mon Sep 17 00:00:00 2001 From: Pavel Begunkov Date: Fri, 29 Nov 2019 00:11:55 +0300 Subject: [PATCH] blk-mq: optimise blk_mq_flush_plug_list() Instead of using list_del_init() in a loop, that generates a lot of unnecessary memory read/writes, iterate from the first request of a batch and cut out a sublist with list_cut_before(). Apart from removing the list node initialisation part, this is more register-friendly, and the assembly uses the stack less intensively. list_empty() at the beginning is done with hope, that the compiler can optimise out the same check in the following list_splice_init(). Signed-off-by: Pavel Begunkov Signed-off-by: Jens Axboe --- block/blk-mq.c | 57 +++++++++++++++++--------------------------------- 1 file changed, 19 insertions(+), 38 deletions(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index f32a3cfdd34e..3c71d52b6401 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1678,14 +1678,10 @@ static int plug_rq_cmp(void *priv, struct list_head *a, struct list_head *b) 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_queue *this_q; - struct request *rq; LIST_HEAD(list); - LIST_HEAD(rq_list); - unsigned int depth; + if (list_empty(&plug->mq_list)) + return; list_splice_init(&plug->mq_list, &list); if (plug->rq_count > 2 && plug->multiple_queues) @@ -1693,42 +1689,27 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule) plug->rq_count = 0; - this_q = NULL; - this_hctx = NULL; - this_ctx = NULL; - depth = 0; - - while (!list_empty(&list)) { - rq = list_entry_rq(list.next); - list_del_init(&rq->queuelist); - BUG_ON(!rq->q); - if (rq->mq_hctx != this_hctx || rq->mq_ctx != this_ctx) { - if (this_hctx) { - trace_block_unplug(this_q, depth, !from_schedule); - blk_mq_sched_insert_requests(this_hctx, this_ctx, - &rq_list, - from_schedule); - } - - this_q = rq->q; - this_ctx = rq->mq_ctx; - this_hctx = rq->mq_hctx; - depth = 0; + do { + struct list_head rq_list; + struct request *rq, *head_rq = list_entry_rq(list.next); + struct list_head *pos = &head_rq->queuelist; /* skip first */ + struct blk_mq_hw_ctx *this_hctx = head_rq->mq_hctx; + struct blk_mq_ctx *this_ctx = head_rq->mq_ctx; + unsigned int depth = 1; + + list_for_each_continue(pos, &list) { + rq = list_entry_rq(pos); + BUG_ON(!rq->q); + if (rq->mq_hctx != this_hctx || rq->mq_ctx != this_ctx) + break; + depth++; } - depth++; - list_add_tail(&rq->queuelist, &rq_list); - } - - /* - * If 'this_hctx' is set, we know we have entries to complete - * on 'rq_list'. Do those. - */ - if (this_hctx) { - trace_block_unplug(this_q, depth, !from_schedule); + list_cut_before(&rq_list, &list, pos); + trace_block_unplug(head_rq->q, depth, !from_schedule); blk_mq_sched_insert_requests(this_hctx, this_ctx, &rq_list, from_schedule); - } + } while(!list_empty(&list)); } static void blk_mq_bio_to_request(struct request *rq, struct bio *bio, -- GitLab