linux-kernel - Re: [PATCH v3 0/9] cgroup/cpuset: Add new cpuset partition type & empty effecitve cpus

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Message-ID: <YRGwXw3KW8eFhEa8@mtj.duckdns.org>
Date:   Mon, 9 Aug 2021 12:46:55 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Waiman Long <llong@...hat.com>
Cc:     Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Shuah Khan <shuah@...nel.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>, Phil Auld <pauld@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Michal Koutný <mkoutny@...e.com>
Subject: Re: [PATCH v3 0/9] cgroup/cpuset: Add new cpuset partition type &
 empty effecitve cpus

Hello, Waiman. Sorry about the delay. Was off for a while.

On Tue, Jul 27, 2021 at 05:14:27PM -0400, Waiman Long wrote:
> However, if we have a complicated partition setup with multiple child
> partitions. Invalid cpuset.cpus change in a parent partition will cause all
> the child partitions to become invalid too. That is the scenario that I
> don't want to happen inadvertently. Alternatively, we can restrict those

I don't think there's anything fundamentally wrong with it given the
requirement that userland has to monitor invalid state transitions.
The same mass transition can happen through cpu hotplug operations,
right?

> invalid changes if a child partition exist and let it pass through and make
> it invalid if it is a standalone partition.
> 
> Please let me know which approach do you want me to take.

I think it'd be best if we can stick to some principles rather than
trying to adjust it for specific scenarios. e.g.:

* If a given state can be reached through cpu hot [un]plug, any
  configuration attempt which reaches the same state should be allowed
  with the same end result as cpu hot [un]plug.

* If a given state can't ever be reached in whichever way, the
  configuration attempting to reach such state should be rejected.

Thanks.

-- 
tejun