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Message-ID: <8e0a41e6-8d03-b0ad-02b5-04449c49c470@redhat.com>
Date:   Thu, 28 Jul 2022 10:49:21 -0400
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Subject: Re: [PATCH 2/2] cgroup: Skip subtree root in
 cgroup_update_dfl_csses()
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To:     =?UTF-8?Q?Michal_Koutn=c3=bd?= <mkoutny@suse.com>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20220728005815.1715522-1-longman@redhat.com>
 <20220728005815.1715522-2-longman@redhat.com>
 <20220728144426.GA26631@blackbody.suse.cz>
From:   Waiman Long <longman@redhat.com>
In-Reply-To: <20220728144426.GA26631@blackbody.suse.cz>
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On 7/28/22 10:44, Michal Koutný wrote:
> On Wed, Jul 27, 2022 at 08:58:15PM -0400, Waiman Long <longman@redhat.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@suse.com>
>
Thanks for the review.

Cheers,
Longman