Re: [PATCH v2.5 3/6] scsi_debug: add multiple queue support

[Hannes Reinecke <hare@suse.de>]

On 05/01/2016 04:44 AM, Douglas Gilbert wrote:
> Add submit_queue parameter (minimum and default: 1; maximum:
> nr_cpu_ids) that controls how many queues are built, each with
> their own lock and in_use bit vector. Add statistics parameter
> which is default on.
> 
> Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
> ---
>  drivers/scsi/scsi_debug.c | 680 +++++++++++++++++++++++++++++-----------------
>  1 file changed, 426 insertions(+), 254 deletions(-)
> 
Two general questions for this:

- Why do you get rid of the embedded command payload?
  Where's the benefit of allocating the commands yourself?
- Wouldn't it be better to move to a per-cpu structure per queue?
  Each queue will be tacked to a CPU anyway, so you could be using
  per-cpu structures. Otherwise you'll run into synchronization
  issues, and any performance gain you might get from scsi-mq is
  lost as you to synchronize on the lower level.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
--
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html