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

[Ming Lei]

On Mon, Jan 29, 2018 at 12:56:30PM -0800, James Bottomley wrote:
> On Mon, 2018-01-29 at 23:46 +0800, Ming Lei wrote:
> [...]
> > 2. When to enable SCSI_MQ at default again?
> 
> I'm not sure there's much to discuss ... I think the basic answer is as
> soon as Christoph wants to try it again.

I guess Christoph still need to evaluate if there are existed issues or
blockers before trying it again. And more input may be got from F2F
discussion, IMHO.

> 
> > 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.
> 
> Is the blocker bug just not closed because no-one thought to do it:
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=178381
> 
> (we have confirmed that this issue is now fixed with the original
> reporter?)

>From a developer view, this issue is fixed by the following commit:
3a0a52997(block, scsi: Make SCSI quiesce and resume work reliably),
and it is verified by kernel list reporter.

> 
> And did the Huawei guy (Jonathan Cameron) confirm his performance issue
> was fixed (I don't think I saw email that he did)?

Last time I talked with John Garry about the issue, and the merged .get_budget
based patch improves much on the IO performance, but there is still a bit gap
compared with legacy path. Seems a driver specific issue, remembered that removing
a driver's lock can improve performance much.

Garry, could you provide further update on this issue?

Thanks,
Ming