[PATCH] scsi_debug: Use scsi-mq if it has been enabled

[PATCH] scsi_debug: Use scsi-mq if it has been enabled

[Bart Van Assche]

Since we want to remove the single queue code from the SCSI core
at the appropriate time and since scsi-mq performs better than
scsi-sq even when using only a single hardware queue, use scsi-mq
if it has been enabled.

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Douglas Gilbert <dgilbert@interlog.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Christoph Hellwig <hch@lst.de>
---
 drivers/scsi/scsi_debug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index a5986dae9020..40df3eea72c8 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -5782,7 +5782,7 @@ static int sdebug_driver_probe(struct device * dev)
 	}
 	/* Decide whether to tell scsi subsystem that we want mq */
 	/* Following should give the same answer for each host */
-	sdebug_mq_active = shost_use_blk_mq(hpnt) && (submit_queues > 1);
+	sdebug_mq_active = shost_use_blk_mq(hpnt);
 	if (sdebug_mq_active)
 		hpnt->nr_hw_queues = submit_queues;
 
-- 
2.15.1

Re: [PATCH] scsi_debug: Use scsi-mq if it has been enabled

[Douglas Gilbert]

On 2018-01-23 07:39 PM, Bart Van Assche wrote:
> Since we want to remove the single queue code from the SCSI core
> at the appropriate time and since scsi-mq performs better than
> scsi-sq even when using only a single hardware queue, use scsi-mq
> if it has been enabled.
> 
> Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
> Cc: Douglas Gilbert <dgilbert@interlog.com>
> Cc: Hannes Reinecke <hare@suse.com>
> Cc: Christoph Hellwig <hch@lst.de>

Acked: Douglas Gilbert <dgilbert@interlog.com>

> ---
>   drivers/scsi/scsi_debug.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
> index a5986dae9020..40df3eea72c8 100644
> --- a/drivers/scsi/scsi_debug.c
> +++ b/drivers/scsi/scsi_debug.c
> @@ -5782,7 +5782,7 @@ static int sdebug_driver_probe(struct device * dev)
>   	}
>   	/* Decide whether to tell scsi subsystem that we want mq */
>   	/* Following should give the same answer for each host */
> -	sdebug_mq_active = shost_use_blk_mq(hpnt) && (submit_queues > 1);
> +	sdebug_mq_active = shost_use_blk_mq(hpnt);
>   	if (sdebug_mq_active)
>   		hpnt->nr_hw_queues = submit_queues;
>   
> 

Re: [PATCH] scsi_debug: Use scsi-mq if it has been enabled

[Christoph Hellwig]

On Tue, Jan 23, 2018 at 04:39:58PM -0800, Bart Van Assche wrote:
> Since we want to remove the single queue code from the SCSI core
> at the appropriate time and since scsi-mq performs better than
> scsi-sq even when using only a single hardware queue, use scsi-mq
> if it has been enabled.

scsi_debug already always uses scsi-mq if enabled.  The somewhat
misnamed sdebug_mq_active variable is only used for decoding
multiqueue tags.  That being said the blk_mq_unique_tag* helpers
should be safe to use even without blk-mq, so the variable could
probably just be removed entirely.

Re: [PATCH] scsi_debug: Use scsi-mq if it has been enabled

[Bart Van Assche]

On Fri, 2018-01-26 at 08:58 +0100, Christoph Hellwig wrote:
> scsi_debug already always uses scsi-mq if enabled.  The somewhat
> misnamed sdebug_mq_active variable is only used for decoding
> multiqueue tags.  That being said the blk_mq_unique_tag* helpers
> should be safe to use even without blk-mq, so the variable could
> probably just be removed entirely.

Hello Christoph,

Removing sdebug_mq_active sounds like a good idea to me. I will rework this
patch.

Bart.