linux-kernel - Re: [PATCH 2/2] cgroup: Skip subtree root in cgroup_update_dfl

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Date:   Thu, 28 Jul 2022 10:49:21 -0400
From:   Waiman Long <longman@...hat.com>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] cgroup: Skip subtree root in
 cgroup_update_dfl_csses()


On 7/28/22 10:44, Michal Koutný wrote:
> On Wed, Jul 27, 2022 at 08:58:15PM -0400, Waiman Long <longman@...hat.com> wrote:
>> The cgroup_update_dfl_csses() function updates css associations when a
>> cgroup's subtree_control file is modified. Any changes made to a cgroup's
>> subtree_control file, however, will only affect its descendants but not
>> the cgroup itself.
> I find this correct.
>
>> So there is no point in migrating csses associated with that cgroup.
>> We can skip them instead.
> Alone it's not such a big win but it componds with the recent Tejun's
> threadgroup_rwsem elision.
>
It is more an optimization patch trying to not waste cpu time doing 
unnecessary work.
>> ---
>>   kernel/cgroup/cgroup.c | 9 +++++++++
>>   1 file changed, 9 insertions(+)
> Feel free to have
> Reviewed-by: Michal Koutný <mkoutny@...e.com>
>
Thanks for the review.

Cheers,
Longman