linux-kernel - Re: [PATCH v11 7/9] cpuset: Expose cpus.effective and mems.effective on cgroup v2 root

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Date:   Thu, 19 Jul 2018 10:04:54 -0400
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>, Tejun Heo <tj@...nel.org>
Cc:     Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Ingo Molnar <mingo@...hat.com>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        kernel-team@...com, pjt@...gle.com, luto@...capital.net,
        Mike Galbraith <efault@....de>, torvalds@...ux-foundation.org,
        Roman Gushchin <guro@...com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [PATCH v11 7/9] cpuset: Expose cpus.effective and mems.effective
 on cgroup v2 root

On 07/19/2018 09:52 AM, Peter Zijlstra wrote:
> On Tue, Jul 03, 2018 at 08:58:23AM -0700, Tejun Heo wrote:
>> Hello, Waiman.
>>
>> On Tue, Jul 03, 2018 at 08:41:31AM +0800, Waiman Long wrote:
>>>> So, effective changing when enabling partition on a child feels wrong
>>>> to me.  It's supposed to contain what's actually allowed to the cgroup
>>>> from its parent and that shouldn't change regardless of how those
>>>> resources are used.  It's still given to the cgroup from its parent.
>>> Another way to work around this issue is to expose the reserved_cpus in
>>> the parent for holding CPUs that can taken by a chid partition. That
>>> will require adding one more cpuset file for those cgroups that are
>>> partition roots.
>> Yeah, that should work.
>>
>>> I don't mind restricting that to the first level children for now. That
>>> does restrict where we can put the container root if we want a separate
>>> partition for a container. Let's hear if others have any objection about
>>> that.
>> As currently implemented, partioning locks away the cpus which should
>> be a system level decision, not container level, so it makes sense to
>> me that it is only available to system root.
> I'm terribly confused, what?!
>
> Why would a container not be allowed to create partitions for its
> various RT workloads?

As far as I understand, Tejun has some concern about the way that
partitioning works is inconsistent with how other resources are being
managed by cgroup v2 controllers. I adds an incremental patch to
temporarily disable the creation of partition below the first level
children to buy us time so that we can reach a compromise later on what
to do. We can always add features, but taking away features after they
are made available will be hard.

I am fine either way. It is up to you and Tejun to figure out what
should be made available to the users.

Cheers,
Longman