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

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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@xxxxxxxxxx>
Cc: Kashyap Desai <kashyap.desai@xxxxxxxxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxx>
Cc: Bart Van Assche <bvanassche@xxxxxxx>
Cc: Long Li <longli@xxxxxxxxxxxxx>
Cc: John Garry <john.garry@xxxxxxxxxx>
Cc: linux-block@xxxxxxxxxxxxxxx
Reported-by: Long Li <longli@xxxxxxxxxxxxx>
Tested-by: Kashyap Desai <kashyap.desai@xxxxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
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@xxxxxxx>

Cheers,

Hannes
--
Dr. Hannes Reinecke                Kernel Storage Architect
hare@xxxxxxx                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer



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