On Mon, Jan 29, 2018 at 03:40:31PM -0500, Mike Snitzer wrote:

On Mon, Jan 29 2018 at 10:46am -0500,
Ming Lei [off-list ref] wrote:
 

quoted

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
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