linux-kernel - Re: [PATCH v4] cpuset: Enable cpuset controller in default hierarchy

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Date:   Fri, 09 Mar 2018 20:40:24 +0100
From:   Mike Galbraith <efault@....de>
To:     Waiman Long <longman@...hat.com>, Tejun Heo <tj@...nel.org>,
        Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, kernel-team@...com, pjt@...gle.com,
        luto@...capital.net, torvalds@...ux-foundation.org,
        Roman Gushchin <guro@...com>
Subject: Re: [PATCH v4] cpuset: Enable cpuset controller in default hierarchy

On Fri, 2018-03-09 at 13:20 -0500, Waiman Long wrote:
> On 03/09/2018 01:17 PM, Mike Galbraith wrote:
> > On Fri, 2018-03-09 at 12:45 -0500, Waiman Long wrote:
> >> On 03/09/2018 11:34 AM, Mike Galbraith wrote:
> >>> On Fri, 2018-03-09 at 10:35 -0500, Waiman Long wrote:
> >>>> Given the fact that thread mode had been merged into 4.14, it is now
> >>>> time to enable cpuset to be used in the default hierarchy (cgroup v2)
> >>>> as it is clearly threaded.
> >>>>
> >>>> The cpuset controller had experienced feature creep since its
> >>>> introduction more than a decade ago. Besides the core cpus and mems
> >>>> control files to limit cpus and memory nodes, there are a bunch of
> >>>> additional features that can be controlled from the userspace. Some of
> >>>> the features are of doubtful usefulness and may not be actively used.
> >>> One rather important features is the ability to dynamically partition a
> >>> box and isolate critical loads.  How does one do that with v2?
> >>>
> >>> In v1, you create two or more exclusive sets, one for generic
> >>> housekeeping, and one or more for critical load(s), RT in my case,
> >>> turning off load balancing in the critical set(s) for obvious reasons.
> >> This patch just serves as a foundation for cpuset support in v2. I am
> >> not excluding the fact that more v1 features will be added in future
> >> patches. We want to start with a clean slate and add on it after careful
> >> consideration. There are some v1 cpuset features that are not used or
> >> rarely used. We certainly want to get rid of them, if possible.
> > If v2 is to ever supersede v1, as is the normal way of things, core
> > functionality really should be on the v2 boat when it sails.  What you
> > left standing on the dock is critical core cpuset functionality.
> >
> > 	-Mike
> 
> From your perspective, what are core functionality that should be
> included in cpuset v2 other than the ability to restrict cpus and memory
> nodes.

Exclusive sets are essential, no?  How else can you manage set wide
properties such as topology (and hopefully soonish nohz).  You clearly
can't have overlapping sets, one having scheduler topology, the other
having none.  Whatever the form, something as core as the capability to
dynamically partition and isolate should IMO be firmly aboard the v2
boat before it sails.

	-Mike