linux-kernel - Re: [PATCH v4 7/9] sched/fair: allow changing cgroup of new forked task

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Message-ID: <Yvq2ZiQL/iHNAaLh@slm.duckdns.org>
Date:   Mon, 15 Aug 2022 11:11:02 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Chengming Zhou <zhouchengming@...edance.com>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 7/9] sched/fair: allow changing cgroup of new forked
 task

On Mon, Aug 08, 2022 at 08:57:43PM +0800, Chengming Zhou wrote:
> commit 7dc603c9028e ("sched/fair: Fix PELT integrity for new tasks")
> introduce a TASK_NEW state and an unnessary limitation that would fail
> when changing cgroup of new forked task.
> 
> Because at that time, we can't handle task_change_group_fair() for new
> forked fair task which hasn't been woken up by wake_up_new_task(),
> which will cause detach on an unattached task sched_avg problem.
> 
> This patch delete this unnessary limitation by adding check before do
> detach or attach in task_change_group_fair().
> 
> So cpu_cgrp_subsys.can_attach() has nothing to do for fair tasks,
> only define it in #ifdef CONFIG_RT_GROUP_SCHED.
> 
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>

I don't know cfs enough to review this but it'd be really great to remove
this restriction.

Thanks.

-- 
tejun