linux-kernel - Re: [PATCH 1/2] cgroup/cpuset: Make cpuset hotplug processing synchronous

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Date: Wed, 3 Apr 2024 11:10:37 -0400
From: Waiman Long <longman@...hat.com>
To: Michal Koutný <mkoutny@...e.com>
Cc: Valentin Schneider <vschneid@...hat.com>, Tejun Heo <tj@...nel.org>,
 Zefan Li <lizefan.x@...edance.com>, Johannes Weiner <hannes@...xchg.org>,
 Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>, Len Brown <len.brown@...el.com>,
 Pavel Machek <pavel@....cz>, Shuah Khan <shuah@...nel.org>,
 linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
 linux-pm@...r.kernel.org, linux-kselftest@...r.kernel.org,
 Frederic Weisbecker <frederic@...nel.org>,
 "Paul E. McKenney" <paulmck@...nel.org>, Ingo Molnar <mingo@...nel.org>,
 Anna-Maria Behnsen <anna-maria@...utronix.de>, Alex Shi <alexs@...nel.org>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Barry Song <song.bao.hua@...ilicon.com>
Subject: Re: [PATCH 1/2] cgroup/cpuset: Make cpuset hotplug processing
 synchronous

On 4/3/24 10:56, Michal Koutný wrote:
> On Wed, Apr 03, 2024 at 10:47:33AM -0400, Waiman Long <longman@...hat.com> wrote:
>> should be rare these days as it will only apply in the case of cgroup
>> v1 under certain condtion,
> Could the migration be simply omitted it those special cases?
>
> (Tasks remain in cpusets with empty cpusets -- that already happens in
> with the current patch before workqueue is dispatched.)

The tasks should not be runnable if there is no CPUs left in their v1 
cpuset. Migrating them to a parent with runnable CPUs is the current way 
which I don't want to break. Alternatively, we could force it to fall 
back to cgroup v2 behavior using the CPUs in their parent cpuset.

Cheers,
Longman

>
> Michal