linux-kernel - Re: [External] Re: [PATCH v2 04/10] sched/fair: remove redundant cpu_cgrp

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Message-ID: <00d2373c-4b80-64a7-740c-dae87a565fe3@bytedance.com>
Date:   Thu, 14 Jul 2022 21:06:04 +0800
From:   Chengming Zhou <zhouchengming@...edance.com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>, mingo@...hat.com,
        peterz@...radead.org, vincent.guittot@...aro.org,
        rostedt@...dmis.org, bsegall@...gle.com, vschneid@...hat.com
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH v2 04/10] sched/fair: remove redundant
 cpu_cgrp_subsys->fork()

On 2022/7/14 20:31, Dietmar Eggemann wrote:
> On 13/07/2022 06:04, Chengming Zhou wrote:
>> We use cpu_cgrp_subsys->fork() to set task group for the new fair task
>> in cgroup_post_fork().
>>
>> Since commit b1e8206582f9 ("sched: Fix yet more sched_fork() races")
>> has already set task group for the new fair task in sched_cgroup_fork(),
>> so cpu_cgrp_subsys->fork() can be removed.
>>
>>   cgroup_can_fork()	--> pin parent's sched_task_group
>>   sched_cgroup_fork()
> 
> Don't we set the task group (`p->sched_task_group = tg`) now directly in
> sched_cgroup_fork() and not in __set_task_cpu()?

Correct, it's my fault, what I want to say is "__set_task_cpu() --> set_task_rq()".
I will fix it next version.

> 
>>     __set_task_cpu	--> set task group
>>   cgroup_post_fork()
>>     ss->fork() := cpu_cgroup_fork()	--> set again
> 
> nit pick:
> 
> cpu_cgroup_fork() -> sched_change_group(..., TASK_SET_GROUP)

Ok, will add this.

Thanks.

> 
>> After this patch's change, task_change_group_fair() only need to
>> care about task cgroup migration, make the code much simplier.
>>
>> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
>> Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
> 
> LGTM too.
> 
> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>
> 
> [...]