linux-kernel - Re: [PATCH V2 00/22] Replace the CFQ I/O Scheduler with BFQ

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Message-id: <17539224.xnQ9OR2lcz@amdc1976>
Date:   Mon, 05 Sep 2016 17:56:35 +0200
From:   Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Mark Brown <broonie@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        Paolo Valente <paolo.valente@...aro.org>,
        linux-block@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Omar Sandoval <osandov@...com>
Subject: Re: [PATCH V2 00/22] Replace the CFQ I/O Scheduler with BFQ

Hi,

On Thursday, September 01, 2016 10:39:46 AM Linus Walleij wrote:
> On Thu, Sep 1, 2016 at 12:09 AM, Mark Brown <broonie@...nel.org> wrote:
> 
> >  - Do some benchmarks on the current status of the various branches on
> >    relevant hardware (including trying to convert some of these slower
> >    devices to blk-mq and seeing what happens).  Linus has been working
> >    on this already in the context of MMC.
> 
> I'm trying to do a patch switching MMC to use blk-mq, so I can
> benchmark performance before/after this.
> 
> While we expect mq to perform worse on single-hardware-queue
> devices like these, we don't know until we tried, so I'm trying.

I did this (switched MMC to blk-mq) some time ago.  Patches are
extremely ugly and hacky (basically the whole MMC block layer
glue code needs to be re-done) so I'm rather reluctant to
sharing them yet (to be honest I would like to rewrite them
completely before posting).

I only did linear read tests (using dd) so far and results that
I got were mixed (BTW the hardware I'm doing this work on is
Odroid-XU3).  Pure block performance under maximum CPU frequency
was slightly worse (5-12%) but the CPU consumption was reduced so
when CPU was scaled down manually (or ondemand CPUfreq governor
was used) blk-mq mode results were better then vanilla ones (up
to 10% when CPU was scaled down to minimum frequency and even
up to 50% when using ondemand governor - this finding is very
interesting and needs to be investigated further).

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics