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

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Date:   Thu, 04 Oct 2018 13:09:06 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Alan Cox <gnomes@...rguk.ukuu.org.uk>
Cc:     Paolo Valente <paolo.valente@...aro.org>,
        Jens Axboe <axboe@...nel.dk>,
        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>
Subject: Re: [PATCH] block: BFQ default for single queue devices

On Thu, 2018-10-04 at 20:25 +0100, Alan Cox wrote:
> > I agree with Jens that it's best to leave it to the Linux distributors to
> > select a default I/O scheduler.
> 
> That assumes such a thing exists. The kernel knows what devices it is
> dealing with. The kernel 'default' ought to be 'whatever is usually best
> for this device'. A distro cannot just pick a correct single default
> because NVME and USB sticks are both normal and rather different in needs.

Which I/O scheduler works best also depends which workload the user will run.
BFQ has significant advantages for interactive workloads like video replay
with concurrent background I/O but probably slows down kernel builds. That's
why I'm not sure whether the kernel should select the default I/O scheduler.

Bart.