linux-kernel - Re: [PATCH RFC 01/14] block, bfq: introduce the BFQ-v0 I/O scheduler as an extra scheduler

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Date:   Sun, 5 Mar 2017 17:02:19 +0100
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Tejun Heo <tj@...nel.org>, Fabio Checconi <fchecconi@...il.com>,
        Arianna Avanzini <avanzini.arianna@...il.com>,
        linux-block@...r.kernel.org,
        Linux-Kernal <linux-kernel@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>, broonie@...nel.org
Subject: Re: [PATCH RFC 01/14] block, bfq: introduce the BFQ-v0 I/O scheduler as an extra scheduler


> Il giorno 05 mar 2017, alle ore 16:16, Jens Axboe <axboe@...nel.dk> ha scritto:
> 
> On 03/04/2017 09:01 AM, Paolo Valente wrote:
>> We tag as v0 the version of BFQ containing only BFQ's engine plus
>> hierarchical support. BFQ's engine is introduced by this commit, while
>> hierarchical support is added by next commit. We use the v0 tag to
>> distinguish this minimal version of BFQ from the versions containing
>> also the features and the improvements added by next commits. BFQ-v0
>> coincides with the version of BFQ submitted a few years ago [1], apart
>> from the introduction of preemption, described below.
>> 
>> BFQ is a proportional-share I/O scheduler, whose general structure,
>> plus a lot of code, are borrowed from CFQ.
> 
> I'll take a closer look at this in the coming week.

ok

> But one quick
> comment - don't default to BFQ. Both because it might not be fully
> stable yet, and also because the performance limitation of it is
> quite severe. Whereas deadline doesn't really hurt single queue
> flash at all, BFQ will.
> 

Ok, sorry.  I was doubtful on what to do, but, to not bother you on
every details, I went for setting it as default, because I thought
people would have preferred to test it, even from boot, in this
preliminary stage.  I reset elevator.c in the submission, unless you
want me to do it even before receiving your and others' reviews.

> Generally, I think that sort of logic should go into a udev rule. If
> a device is rotational it should default to BFQ once the dust has
> settled.
> 

ok

Looking forward for your feedback,
Paolo

> -- 
> Jens Axboe
>