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 15:52:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Waiman Long <longman@...hat.com>, 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 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?