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

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

[Ming Lei]

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.

Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Mike Snitzer <snitzer@redhat.com>
Fixes: c616cbee97ae ("blk-mq: punt failed direct issue to dispatch list")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 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 c3856377b961..b356d4d3ca0b 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2016,7 +2016,8 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 	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;
 }
 
-- 
2.25.2

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

[Ming Lei]

On Wed, Jul 29, 2020 at 03:24:49PM +0800, Ming Lei wrote:
> 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.
> 
> Cc: Bart Van Assche <bvanassche@acm.org>
> Cc: Mike Snitzer <snitzer@redhat.com>
> Fixes: c616cbee97ae ("blk-mq: punt failed direct issue to dispatch list")
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  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 c3856377b961..b356d4d3ca0b 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2016,7 +2016,8 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
>  	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;
>  }
>  

Hello Guys,

Ping...


thanks, 
Ming