linux-kernel - [PATCH v2 3/3] blk-mq: optimise *end

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Date:   Wed, 13 Oct 2021 09:57:13 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Christoph Hellwig <hch@...radead.org>, asml.silence@...il.com
Subject: [PATCH v2 3/3] blk-mq: optimise *end_request non-stat path

We already have a blk_mq_need_time_stamp() check in
__blk_mq_end_request() to get a timestamp, hide all the statistics
accounting under it. It cuts some cycles for requests that don't need
stats, and is free otherwise.

Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
---
 block/blk-mq.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 38e6651d8b94..3dd3b22bc280 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -572,20 +572,18 @@ void blk_mq_free_plug_rqs(struct blk_plug *plug)
 
 inline void __blk_mq_end_request(struct request *rq, blk_status_t error)
 {
-	u64 now = 0;
+	if (blk_mq_need_time_stamp(rq)) {
+		u64 now = ktime_get_ns();
 
-	if (blk_mq_need_time_stamp(rq))
-		now = ktime_get_ns();
+		if (rq->rq_flags & RQF_STATS) {
+			blk_mq_poll_stats_start(rq->q);
+			blk_stat_add(rq, now);
+		}
 
-	if (rq->rq_flags & RQF_STATS) {
-		blk_mq_poll_stats_start(rq->q);
-		blk_stat_add(rq, now);
+		blk_mq_sched_completed_request(rq, now);
+		blk_account_io_done(rq, now);
 	}
 
-	blk_mq_sched_completed_request(rq, now);
-
-	blk_account_io_done(rq, now);
-
 	if (rq->end_io) {
 		rq_qos_done(rq->q, rq);
 		rq->end_io(rq, error);
-- 
2.33.0