Re: [PATCH V4] scsi: core: only re-run queue in scsi_end_request() if device queue is busy

[Hannes Reinecke <hare@suse.de>]

On 8/17/20 12:08 PM, Ming Lei wrote:
> Now the request queue is run in scsi_end_request() unconditionally if both
> target queue and host queue is ready. We should have re-run request queue
> only after this device queue becomes busy for restarting this LUN only.
> 
> Recently Long Li reported that cost of run queue may be very heavy in
> case of high queue depth. So improve this situation by only running
> the request queue when this LUN is busy.
> 
> Cc: Ewan D. Milne <emilne@redhat.com>
> Cc: Kashyap Desai <kashyap.desai@broadcom.com>
> Cc: Hannes Reinecke <hare@suse.de>
> Cc: Bart Van Assche <bvanassche@acm.org>
> Cc: Long Li <longli@microsoft.com>
> Cc: John Garry <john.garry@huawei.com>
> Cc: linux-block@vger.kernel.org
> Reported-by: Long Li <longli@microsoft.com>
> Tested-by: Kashyap Desai <kashyap.desai@broadcom.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
> V4:
> 	- fix one race reported by Kashyap, and simplify the implementation
> 	a bit; also pass Kashyap's both function and performance test
> V3:
> 	- add one smp_mb() in scsi_mq_get_budget() and comment
> 
> V2:
> 	- commit log change, no any code change
> 	- add reported-by tag
> 
>   drivers/scsi/scsi_lib.c    | 51 +++++++++++++++++++++++++++++++++++---
>   include/scsi/scsi_device.h |  1 +
>   2 files changed, 49 insertions(+), 3 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
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