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

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Message-ID: <c1d07f31-40e7-0fb0-7251-24067564a0ad@kernel.dk>
Date:   Wed, 22 Feb 2017 11:44:41 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "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 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).
2) The individual schedulers will be y/m/n selectable, just like any
   other driver.

I hope that works for everyone.

-- 
Jens Axboe