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

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Message-Id: <5CC62643-A46B-4BD5-B6ED-AD767926643B@linaro.org>
Date:   Mon, 5 Sep 2016 22:29:25 +0200
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        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


Il giorno 05/set/2016, alle ore 17:56, Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com> ha scritto:

> 
> 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).
> 

IMO, another important figure of merit is application- and
system-level latency (e.g., application/system responsiveness or frame
drop rate with audio/video playback/streaming, while the device
happens to be busy with furhter I/O). Scripts to measure it can be
found, e.g., here [1] for desktop systems. If I can, I'm willing to
help in any respect.

Thanks,
Paolo

[1] https://github.com/Algodev-github/S

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