linux-kernel - Re: [PATCH] block: BFQ default for single queue devices

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Date:   Wed, 03 Oct 2018 08:54:51 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Paolo Valente <paolo.valente@...aro.org>,
        Jens Axboe <axboe@...nel.dk>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        linux-block <linux-block@...r.kernel.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        linux-mtd@...ts.infradead.org, Pavel Machek <pavel@....cz>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Richard Weinberger <richard@....at>,
        Artem Bityutskiy <dedekind1@...il.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Jan Kara <jack@...e.cz>, Andreas Herrmann <aherrmann@...e.com>,
        Mel Gorman <mgorman@...e.com>,
        Chunyan Zhang <zhang.chunyan@...aro.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        'Paolo Valente' via bfq-iosched 
        <bfq-iosched@...glegroups.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH] block: BFQ default for single queue devices

On Wed, 2018-10-03 at 08:29 +0200, Paolo Valente wrote:
> [1] https://lkml.org/lkml/2017/2/21/791
> [2] http://algo.ing.unimo.it/people/paolo/disk_sched/results.php
> [3] https://lwn.net/Articles/763603/

>From [2]: "BFQ loses about 18% with only random readers, because the number
of IOPS becomes so high that the execution time and parallel efficiency of
the schedulers becomes relevant." Since the number of I/O patterns for which
results are available on [2] is limited and since the number of devices for
which test results are available on [2] is limited (e.g. RAID is missing),
there might be other cases in which configuring BFQ as the default would
introduce a regression.

I agree with Jens that it's best to leave it to the Linux distributors to
select a default I/O scheduler.

Bart.