Re: dm-multipath test scripts

[Hannes Reinecke <hare@suse.de>]

On 02/20/2016 07:12 AM, Mike Snitzer wrote:
> On Fri, Feb 19 2016 at  2:42pm -0500,
> Mike Snitzer <snitzer@redhat.com> wrote:
>
>> On Fri, Feb 19 2016 at  3:37am -0500,
>> Junichi Nomura <j-nomura@ce.jp.nec.com> wrote:
>>
>>> On 02/19/16 09:33, Nomura Junichi wrote:
>>>> On 02/19/16 02:17, Mike Snitzer wrote:
>>>>> What is the last kernel version that your scripts have worked on?
>>>>
>>>> v4.4 worked fine. I'll check with v4.5-rc4 when I get a machine.
>>>
>>> v4.5-rc4 works fine, too.
>>
>> Have you been running with blk-mq?
>> Either by setting CONFIG_DM_MQ_DEFAULT or:
>> echo Y > /sys/module/dm_mod/parameters/use_blk_mq
>>
>> I'm seeing test_02_sdev_delete fail with blk-mq enabled.
>
> I only see failure if I stack dm-mq ontop of old non-mq scsi devices with:
>
> echo N > /sys/module/scsi_mod/parameters/use_blk_mq
> echo Y > /sys/module/dm_mod/parameters/use_blk_mq
>
> If I use scsi-mq for the underlying devices all works fine (been testing
> the latest dm-4.6 branch though, I'll go back and try stock 4.5-rc4 just
> to double check).
>
> But this makes me think the novelty of having dm-mq support stacking on
> non-blk-mq devices was misplaced.  It is a senseless config.  I'll
> probably remove support for such stacking soon (next week).

Hmm. I must admit I really, really don't like these 'once-and-for-all'
parameter.

ATM the only SCSI driver to support SCSI-mq properly are lpfc, virtio, 
and fnic. None of the other driver have been modified, and I suspect the 
performance might be less than stellar.

So there will be configurations where one might want to run scsi-mq 
alongside non-mq HBAs.

I would really love to see to make that more granular so that these 
configurations can run efficiently.
I know Christoph is violently against it, but I don't really see any 
solution presenting itself at the moment.

Maybe a good topic for LSF ...

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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