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Message-ID: <a252d963-aedd-c9fe-e507-2b8fea8d375d@redhat.com>
Date:   Thu, 28 Jul 2022 11:35:26 -0400
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Subject: Re: [PATCH 1/2] cgroup/cpuset: Keep current cpus list if cpus
 affinity was explicitly set
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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>
 <20220728144420.GA27407@blackbody.suse.cz>
 <a58852b4-313a-9271-f31d-f79a91ec188b@redhat.com>
 <20220728152355.GB25894@blackbody.suse.cz>
From:   Waiman Long <longman@redhat.com>
In-Reply-To: <20220728152355.GB25894@blackbody.suse.cz>
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On 7/28/22 11:23, Michal Koutný wrote:
> On Thu, Jul 28, 2022 at 10:59:01AM -0400, Waiman Long <longman@redhat.com> wrote:
>> Cgroup v1 doesn't have this problem.
> v1 analogy would be:
>
> 	echo 2-3 >$dst/cpuset.cpus
> 	# job runs in $dst
> 	# one task T in $dst sets affinity just to one cpu
> 	# I rethink my config, I want to allow $dst more space
> 	echo 2-5 >$dst/cpuset.cpus
>
> Most tasks in $dst happily utilize the new cpus but it breaks affinity
> for T -- this must have been broken since ever.
>
> (Or I'd argue that per-thread affinities are just recommendations, if I
> have a task for nohz CPU, I should enforce its placement with cpuset
> from the beginning.)

I should have clarified that what I meant is systemd on a cgroup v1 
environment doesn't cause this cpu list reset to happen. It doesn't mean 
that cgroup v1 has no similar problem. Sorry for the confusion.

Cheers,
Longman