linux-kernel - Re: [PATCH v10 2/9] cpuset: Add new v2 cpuset.sched.domain

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Message-ID: <20180620142735.GM2494@hirez.programming.kicks-ass.net>
Date:   Wed, 20 Jun 2018 16:27:35 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Tejun Heo <tj@...nel.org>, 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 v10 2/9] cpuset: Add new v2 cpuset.sched.domain_root flag

On Mon, Jun 18, 2018 at 12:14:01PM +0800, Waiman Long wrote:
> +  cpuset.sched.domain_root

Why are we calling this a domain_root and not a partition?

> +	A read-write single value file which exists on non-root
> +	cpuset-enabled cgroups.  It is a binary value flag that accepts
> +	either "0" (off) or "1" (on).  This flag is set by the parent
> +	and is not delegatable.

You still haven't answered:

  https://lkml.kernel.org/r/20180531094943.GG12180@hirez.programming.kicks-ass.net

the question stands.

> +	If set, it indicates that the current cgroup is the root of a
> +	new scheduling domain or partition that comprises itself and
> +	all its descendants except those that are scheduling domain
> +	roots themselves and their descendants.  The root cgroup is
> +	always a scheduling domain root.
> +
> +	There are constraints on where this flag can be set.  It can
> +	only be set in a cgroup if all the following conditions are true.
> +
> +	1) The "cpuset.cpus" is not empty and the list of CPUs are
> +	   exclusive, i.e. they are not shared by any of its siblings.
> +	2) The "cpuset.cpus" is also a proper subset of the parent's
> +	   "cpuset.cpus.effective".
> +	3) The parent cgroup is a scheduling domain root.
> +	4) There is no child cgroups with cpuset enabled.  This is
> +	   for eliminating corner cases that have to be handled if such
> +	   a condition is allowed.
> +
> +	Setting this flag will take the CPUs away from the effective
> +	CPUs of the parent cgroup.  Once it is set, this flag cannot be
> +	cleared if there are any child cgroups with cpuset enabled.
> +
> +	A parent scheduling domain root cgroup cannot distribute
> +	all its CPUs to its child scheduling domain root cgroups.
> +	There must be at least one cpu left in the parent scheduling
> +	domain root cgroup.