linux-kernel - Re: [PATCH v2 09/10] sched/psi: per-cgroup PSI stats disable/re-enable interface

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Date:   Fri, 12 Aug 2022 12:14:44 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Chengming Zhou <zhouchengming@...edance.com>
Cc:     hannes@...xchg.org, tj@...nel.org, corbet@....net,
        surenb@...gle.com, mingo@...hat.com, peterz@...radead.org,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, cgroups@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        songmuchun@...edance.com
Subject: Re: [PATCH v2 09/10] sched/psi: per-cgroup PSI stats
 disable/re-enable interface

Hello Chengming.

On Mon, Aug 08, 2022 at 07:03:40PM +0800, Chengming Zhou <zhouchengming@...edance.com> wrote:
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index dd84e34bc051..ade40506ab80 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -968,6 +968,13 @@ All cgroup core files are prefixed with "cgroup."
>  	killing cgroups is a process directed operation, i.e. it affects
>  	the whole thread-group.
>  
> +  cgroup.psi
> +	A read-write single value file that allowed values are "0" and "1".
> +	The default is "1".
> +
> +	Writing "0" to the file will disable the cgroup PSI stats accounting.
> +	Writing "1" to the file will re-enable the cgroup PSI stats accounting.
> +

I'd suggest explaining here explicitely, this control attribute is not
hierarchical (i.e. PSI accounting in a cgroup does not affect accounting
in descendants and doesn't need pass enablement via ancestors from
root). And the purpose that it "saves" cycles (where).

Regards,
Michal