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

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Date:   Sat, 14 Oct 2017 09:39:21 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Ming Lei <ming.lei@...hat.com>, linux-block@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>
Cc:     Bart Van Assche <bart.vanassche@...disk.com>,
        Laurence Oberman <loberman@...hat.com>,
        Paolo Valente <paolo.valente@...aro.org>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Tom Nguyen <tom81094@...il.com>, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, Omar Sandoval <osandov@...com>,
        John Garry <john.garry@...wei.com>
Subject: Re: [PATCH V10 0/8] blk-mq-sched: improve sequential I/O performance

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.

-- 
Jens Axboe