linux-kernel - Re: [PATCHSET v6] sched: Implement BPF extensible scheduler class

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Date: Wed, 19 Jun 2024 15:55:46 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Tejun Heo <tj@...nel.org>, mingo@...hat.com, peterz@...radead.org, 
	juri.lelli@...hat.com, vincent.guittot@...aro.org, dietmar.eggemann@....com, 
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com, 
	vschneid@...hat.com, ast@...nel.org, daniel@...earbox.net, andrii@...nel.org, 
	martin.lau@...nel.org, joshdon@...gle.com, brho@...gle.com, pjt@...gle.com, 
	derkling@...gle.com, haoluo@...gle.com, dvernet@...a.com, 
	dschatzberg@...a.com, dskarlat@...cmu.edu, riel@...riel.com, 
	changwoo@...lia.com, himadrics@...ia.fr, memxor@...il.com, 
	andrea.righi@...onical.com, joel@...lfernandes.org, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCHSET v6] sched: Implement BPF extensible scheduler class

On Wed, 19 Jun 2024 at 15:27, Thomas Gleixner <tglx@...utronix.de> wrote:
>
> On Wed, Jun 19 2024 at 15:10, Linus Torvalds wrote:
> >
> > The thing is, I have seen absolutely _nothing_ in the last 9 months or
> > so.
>
> Right, but that applies to both sides, no?

But Thomas, this isn't a "both sides" issue.

This is a "people want to do new code and features, and the scheduler
people ARE ACTIVELY HOLDING IT UP" issue.

Yes, part of that "actively holding it up" is trying to make rules for
"you need to do this other XYZ thing to make us happy".

But no, then "not doing XYZ" does *NOT* make it some "but but other side" issue.

This, btw, is not some new thing. It's something that has been
discussed multiple times over the years at the maintainer summit for
different maintainers. When people come in and propose feature X, it's
not kosher to then say "you have to do Y first".

And yes, maybe everybody even agrees that Y would be a good thing, and
yes, wouldn't it be lovely if somebody did it. But the people who
wanted X didn't care about Y, and trying to get Y done by then gating
X is simply not ok.

Now, if there was some technical argument against X itself, that would
be one thing. But the arguments I've heard have basically fallen into
two camps: the political one ("We don't want to do X because we simply
don't want an extensible scheduler, because we want people to work on
_our_ scheduler") and the tying one ("X is ok but we want Y solved
first").

I was hoping the tying argument would get solved. I saw a couple of
half-hearted emails to that effect, and Rik at some point saying
"maybe the problems are solvable", referring to his work from a couple
of years ago, but again, nothing actually happened.

And I don't see the argument that the way to make something happen is
to continue to do nothing.

    https://www.youtube.com/watch?v=lOTyUfOHgas

Because if you are serious about making forward progress *with* the
BPF extensions, why not merge them and actually work with that as the
base?

IOW, what is the argument for _not_ merging it?

                        Linus