Re: [LSF/MM TOPIC] Two blk-mq related topics

[Ming Lei <ming.lei@redhat.com>]

On Mon, Jan 29, 2018 at 03:40:31PM -0500, Mike Snitzer wrote:
> On Mon, Jan 29 2018 at 10:46am -0500,
> Ming Lei <ming.lei@redhat.com> wrote:
>  
> > 2. When to enable SCSI_MQ at default again?
> > 
> > SCSI_MQ is enabled on V3.17 firstly, but disabled at default. In V4.13-rc1,
> > it is enabled at default, but later the patch is reverted in V4.13-rc7, and
> > becomes disabled at default too.
> > 
> > Now both the original reported PM issue(actually SCSI quiesce) and the
> > sequential IO performance issue have been addressed. And MQ IO schedulers
> > are ready too for traditional disks. Are there other issues to be addressed
> > for enabling SCSI_MQ at default? When can we do that again?
> > 
> > Last time, the two issues were reported during V4.13 dev cycle just when it is
> > enabled at default, that seems if SCSI_MQ isn't enabled at default, it wouldn't
> > be exposed to run/tested completely & fully.  
> > 
> > So if we continue to disable it at default, maybe it can never be exposed to
> > full test/production environment.
> 
> I was going to propose revisiting this as well.
> 
> I'd really like to see all the old .request_fn block core code removed.

Yeah, that should be a final goal, but may take a bit long.

> 
> But maybe we take a first step of enabling:
> CONFIG_SCSI_MQ_DEFAULT=Y
> CONFIG_DM_MQ_DEFAULT=Y

Maybe you can remove legacy path from DM_RQ first, and take your
original approach to allow DM/MQ over legacy underlying driver,
seems we discussed this topic before, :-)

Thanks,
Ming