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

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Message-ID: <CAHk-=wgjbNLRtOvcmeEUtBQyJtYYAtvRTROBy9GHeF1Quszfgg@mail.gmail.com>
Date: Thu, 20 Jun 2024 10:11:49 -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 22:07, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> And scx_next_task_picked() isn't pretty - as far as I understand, it's
> because there's only a "class X picked" callback ("pick_next_task()"),
> and no way to tell other classes they weren't picked.

I guess that could be a class callback, something like this:

        p = class->pick_next_task(rq);
        if (p)
        if (p) {
-               scx_next_task_picked(rq, p, class);
+               struct sched_class *prev = last->sched_class;
+               if (class != prev && prev->switch_class)
+                       prev->switch_class(rq);
                return p;
        }

and that would be arguably much prettier. But maybe I've
mis-understood the reason for that scx_next_task_picked() thing.

Tejun?

             Linus