Commit db03f88f authored Aug 18, 2020 by Ming Lei Committed by Jens Axboe Aug 21, 2020

blk-mq: insert request not through ->queue_rq into sw/scheduler queue



c616cbee ("blk-mq: punt failed direct issue to dispatch list") supposed
to add request which has been through ->queue_rq() to the hw queue dispatch
list, however it adds request running out of budget or driver tag to hw queue
too. This way basically bypasses request merge, and causes too many request
dispatched to LLD, and system% is unnecessary increased.

Fixes this issue by adding request not through ->queue_rq into sw/scheduler
queue, and this way is safe because no ->queue_rq is called on this request
yet.

High %system can be observed on Azure storvsc device, and even soft lock
is observed. This patch reduces %system during heavy sequential IO,
meantime decreases soft lockup risk.

Fixes: c616cbee ("blk-mq: punt failed direct issue to dispatch list")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 17bc1030

block/blk-mq.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -2026,7 +2026,8 @@ insert:
		if (bypass_insert)
		return BLK_STS_RESOURCE;

		blk_mq_request_bypass_insert(rq, false, run_queue);
		blk_mq_sched_insert_request(rq, false, run_queue, false);

		return BLK_STS_OK;
		}

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