Re: iSER multi-queue configuration

[Ming Lin <mlin-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

On Sun, 2016-05-01 at 05:53 +0300, Sagi Grimberg wrote:
> > Hi Sagi,
> 
> Hi Ming,
> 
> > I'm looking at why there is only 1 HW queue for iser.
> > 
> > 2185 int scsi_mq_setup_tags(struct Scsi_Host *shost)
> > 2186 {
> > ...
> > 2199         shost->tag_set.nr_hw_queues = shost->nr_hw_queues ? :
> > 1;
> > 
> > 
> > It seems because iser code does not set shost->nr_hw_queues at all.
> > 
> > Why?
> 
> The iscsi driver has not yet been converted to scsi_mq and iser as
> an iscsi transport still does not use multi-queue.

I'm going to compare performance between NVMe over RDMA and SCSI over
RDMA. SRP supports scsi_mq, so I'd use SRP to do the apples-to-apples
comparison.

> 
> In iscsi, a hw queue maps to an iscsi session. In order to support
> multi-queue we need to have iscsi open multiple sessions and map
> a session to a queue.
> 
> I had some preliminary works on this (joint with Mike Christie) but I
> didn't have time thus far to implement a full conversion to scsi-mq.

I'd happy to test it once you done.
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