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

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Message-ID: <9f6e0c1e-fe62-9898-d074-edc05310cebe@kernel.dk>
Date:   Wed, 22 Feb 2017 11:58:58 -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 11:56 AM, Linus Torvalds wrote:
> On Wed, Feb 22, 2017 at 10:52 AM, Jens Axboe <axboe@...nel.dk> wrote:
>>>
>>> It's that simple.
>>
>> No, it's not that simple at all. Fact is, some optimizations make sense
>> for some workloads, and some do not.
> 
> Are you even listening?
> 
> I'm saying no user can ever give a sane answer to your question. The
> question is insane and wrong.
> 
> I already said you can have a dynamic configuration (and maybe even an
> automatic heuristic - like saying that a ramdisk gets NOOP by default,
> real hardware does not).
> 
> But asking a user at kernel config time for a default is insane. If
> *you* cannot answer it, then the user sure as hell cannot.
> 
> Other configuration questions have problems too, but at least the
> question about "should I support ext4" is something a user (or distro)
> can sanely answer. So your comparisons are pure bullshit.

As per the previous email, this was my proposed solution:

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.

Any further settings on that can be done at runtime, through sysfs.

-- 
Jens Axboe