linux-kernel - Re: [GIT PULL] Block pull request for- 4.11-rc1

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Message-ID: <20170222215058.GA291@x4>
Date:   Wed, 22 Feb 2017 22:50:58 +0100
From:   Markus Trippelsdorf <markus@...ppelsdorf.de>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] Block pull request for- 4.11-rc1

On 2017.02.22 at 11:44 -0700, Jens Axboe wrote:
> On 02/22/2017 11:42 AM, Linus Torvalds wrote:
> > On Wed, Feb 22, 2017 at 10:26 AM, Linus Torvalds
> > <torvalds@...ux-foundation.org> wrote:
> >>
> >> And dammit, IF YOU DON'T EVEN KNOW, WHY THE HELL ARE YOU ASKING THE POOR USER?
> > 
> > Basically, I'm pushing back on config options that I can't personally
> > even sanely answer.
> 
> I got that much, and I don't disagree on that part.
> 
> > If it's a config option about "do I have a particular piece of
> > hardware", it makes sense. But these new ones were just complete
> > garbage.
> > 
> > The whole "default IO scheduler" thing is a disease. We should stop
> > making up these shit schedulers and then say "we don't know which one
> > works best for you".
> > 
> > All it does is encourage developers to make shortcuts and create crap
> > that isn't generically useful, and then blame the user and say "well,
> > you should have picked a different scheduler" when they say "this does
> > not work well for me".
> > 
> > We have had too many of those kinds of broken choices.  And when the
> > new Kconfig options get so confusing and so esoteric that I go "Hmm, I
> > have no idea if my hardware does a single queue or not", I put my foot
> > down.
> > 
> > When the IO scheduler questions were about a generic IO scheduler for
> > everything, I can kind of understand them. I think it was still a
> > mistake (for the reasons outline above), but at least it was a
> > comprehensible question to ask.
> > 
> > But when it gets to "what should I do about a single-queue version of
> > a MQ scheduler", the question is no longer even remotely sensible. The
> > question should simply NOT EXIST. There is no possible valid reason to
> > ask that kind of crap.
> 
> OK, so here's what I'll do:
> 
> 1) We'll kill the default scheduler choices. sq blk-mq will default to
>    mq-deadline, mq blk-mq will default to "none" (at least for now, until
>    the new scheduler is done).

But what about e.g. SATA SSDs? Wouldn't they be better off without any
scheduler? 
So perhaps setting "none" for queue/rotational==0 and mq-deadline for
spinning drives automatically in the sq blk-mq case?

-- 
Markus