Re: [PATCH V10 0/8] blk-mq-sched: improve sequential I/O performance

[Ming Lei]

On Sat, Oct 14, 2017 at 09:39:21AM -0600, Jens Axboe wrote:
> On 10/14/2017 03:22 AM, Ming Lei wrote:
> > Hi Jens,
> > 
> > In Red Hat internal storage test wrt. blk-mq scheduler, we found that I/O
> > performance is much bad with mq-deadline, especially about sequential I/O
> > on some multi-queue SCSI devcies(lpfc, qla2xxx, SRP...)
> > 
> > Turns out one big issue causes the performance regression: requests are
> > still dequeued from sw queue/scheduler queue even when ldd's queue is
> > busy, so I/O merge becomes quite difficult to make, then sequential IO
> > performance degrades a lot.
> > 
> > This issue becomes one of mains reasons for reverting default SCSI_MQ
> > in V4.13.
> > 
> > This 8 patches improve this situation, and brings back performance loss.
> > 
> > With this change, SCSI-MQ sequential I/O performance is improved much, Paolo
> > reported that mq-deadline performance improved much[2] in his dbench test
> > wrt V2. Also performance improvement on lpfc/qla2xx was observed with V1.[1]
> 
> Looks good to me, and the kyber fix looks obviously correct to me. I have
> applied this series for 4.15. Thanks Ming.

That is great, thanks for making this patchset in!

-- 
Ming