linux-kernel - Re: [PATCH 06/31] sched: Add sched_class->switching_to() and expose check_class

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Date:   Mon, 12 Dec 2022 12:28:29 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     torvalds@...ux-foundation.org, mingo@...hat.com,
        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, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH 06/31] sched: Add sched_class->switching_to() and expose
 check_class_changing/changed()

On Tue, Nov 29, 2022 at 10:22:48PM -1000, Tejun Heo wrote:
> When a task switches to a new sched_class, the prev and new classes are
> notified through ->switched_from() and ->switched_to(), respectively, after
> the switching is done. However, a new sched_class needs to prepare the task
> state before it is enqueued on the new class for the first time.

How and why isn't sched_fork() sufficient?