blk-mq: insert request not through ->queue_rq into sw/scheduler queue
authorMing Lei <ming.lei@redhat.com>
Tue, 18 Aug 2020 09:07:28 +0000 (17:07 +0800)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Thu, 3 Sep 2020 09:26:54 +0000 (11:26 +0200)
commit872a2b3182ee94e772ae81f2a10f3118f7b36ffe
tree4e5750ad9cdbd24e7ebd180e07eb295ec5fecb00
parent9054d58440927f08efa71c3da211acbdd18e634a
blk-mq: insert request not through ->queue_rq into sw/scheduler queue

[ Upstream commit db03f88fae8a2c8007caafa70287798817df2875 ]

c616cbee97ae ("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: c616cbee97ae ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
block/blk-mq.c