[PATCH 5.4 105/214] blk-mq: insert request not through ->queue_rq into sw/scheduler queue

Greg Kroah-Hartman
2020-09-01T16:22:40Z

From: Ming Lei <ming.lei@redhat.com>

[ 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 | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index ae7d31cb5a4e1..8f67f0f16ec2e 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1869,7 +1869,8 @@ 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;
}

--
2.25.1