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

[Ming Lei <ming.lei@redhat.com>]

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