From: "Michal Koutný" <mkoutny@suse.com>
To: Waiman Long <longman@redhat.com>
Cc: Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Jonathan Corbet <corbet@lwn.net>, Shuah Khan <shuah@kernel.org>,
cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Roman Gushchin <guro@fb.com>, Phil Auld <pauld@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Frederic Weisbecker <frederic@kernel.org>,
Marcelo Tosatti <mtosatti@redhat.com>
Subject: Re: [PATCH v8 5/6] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst
Date: Tue, 16 Nov 2021 18:54:11 +0100 [thread overview]
Message-ID: <20211116175411.GA50019@blackbody.suse.cz> (raw)
In-Reply-To: <8f68692b-bd8f-33fd-44ae-f6f83bf2dc00@redhat.com>
On Mon, Nov 15, 2021 at 04:10:29PM -0500, Waiman Long <longman@redhat.com> wrote:
> > On Mon, Oct 18, 2021 at 10:36:18AM -0400, Waiman Long <longman@redhat.com> wrote:
> > > + scheduler. Tasks in such a partition must be explicitly bound
> > > + to each individual CPU.
> [...]
>
> It can be a problem when one is trying to move from one cgroup to another
> cgroup with non-overlapping cpus laterally. However, if a task is initially
> from a parent cgroup with affinity mask that include cpus in the isolated
> child cgroup, I believe it should be able to move to the isolated child
> cgroup without problem. Otherwise, it is a bug that needs to be fixed.
app_root cpuset.cpus=0-3
`- non_rt cpuset.cpus=0-1 cpuset.cpus.partition=member
`- rt cpuset.cpus=2-3 cpuset.cpus.partition=isolated
The app_root would have cpuset.cpus.effective=0-1 so even the task in
app_root can't sched_setaffinity() to cpus 2-3.
But AFAICS, the migration calls set_cpus_allowed_ptr() anyway, so the
task in the isolated partition needn't to bind explicitly with
sched_setaffinity(). (It'd have two cpus available, so one more
sched_setaffinity() or migration into a single-cpu list is desirable.)
All in all, I think the behavior is OK and the explicit binding of tasks
in an isolated cpuset is optional (not a must as worded currently).
> I think the wording may be confusing. What I meant is none of the requested
> cpu can be granted. So if there is at least one granted, the effective cpus
> won't be empty.
Ack.
> You currently cannot make change to cpuset.cpus that violates the cpu
> exclusivity rule. The above constraints will not disallow you to make the
> change. They just affect the validity of the partition root.
Sibling exclusivity should be a validity condition regardless of whether
transition is allowed or not. (At least it looks simpler to me.)
> > > + Changing a partition root to "member" is always allowed.
> > > + If there are child partition roots underneath it, however,
> > > + they will be forced to be switched back to "member" too and
> > > + lose their partitions. So care must be taken to double check
> > > + for this condition before disabling a partition root.
> > (Or is this how delegation is intended?) However, AFAICS, parent still
> > can't remove cpuset.cpus even when the child is a "member". Otherwise,
> > I agree with the back-switch.
> There are only 2 possibilities here. Either we force the child partitions to
> be become members or invalid partition root.
My point here was mostly about preempting the cpus (as a v2 specific
feature). (I'm rather indifferent whether children turn into invalid
roots or members.)
Thanks,
Michal
next prev parent reply other threads:[~2021-11-16 17:54 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-18 14:36 [PATCH v8 0/6] cgroup/cpuset: Add new cpuset partition type & empty effecitve cpus Waiman Long
2021-10-18 14:36 ` [PATCH v8 1/6] cgroup/cpuset: Allow no-task partition to have empty cpuset.cpus.effective Waiman Long
2021-10-18 14:36 ` [PATCH v8 2/6] cgroup/cpuset: Refining features and constraints of a partition Waiman Long
2021-10-18 14:36 ` [PATCH v8 3/6] cgroup/cpuset: Add a new isolated cpus.partition type Waiman Long
2021-10-18 14:36 ` [PATCH v8 4/6] cgroup/cpuset: Show invalid partition reason string Waiman Long
2021-10-18 14:36 ` [PATCH v8 5/6] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst Waiman Long
2021-11-15 19:31 ` Michal Koutný
2021-11-15 20:11 ` Tejun Heo
2021-11-15 21:27 ` Waiman Long
2021-11-15 21:10 ` Waiman Long
2021-11-16 17:54 ` Michal Koutný [this message]
2021-11-30 15:35 ` Waiman Long
2021-11-30 17:11 ` Tejun Heo
2021-12-01 3:56 ` Waiman Long
2021-12-01 14:13 ` Michal Koutný
2021-12-01 14:56 ` Waiman Long
2021-12-01 16:39 ` Tejun Heo
2021-12-01 17:49 ` Waiman Long
2021-12-01 14:26 ` Waiman Long
2021-12-01 16:46 ` Tejun Heo
2021-12-01 18:05 ` Waiman Long
2021-12-02 1:28 ` Waiman Long
2021-12-03 18:25 ` Michal Koutný
2021-12-03 19:27 ` Waiman Long
2021-10-18 14:36 ` [PATCH v8 6/6] kselftest/cgroup: Add cpuset v2 partition root state test Waiman Long
2021-10-27 23:05 ` [PATCH v8 0/6] cgroup/cpuset: Add new cpuset partition type & empty effecitve cpus Waiman Long
2021-11-10 11:13 ` Felix Moessbauer
2021-11-10 13:21 ` Marcelo Tosatti
2021-11-10 13:56 ` Michal Koutný
2021-11-10 15:21 ` Moessbauer, Felix
2021-11-10 16:10 ` Marcelo Tosatti
2021-11-10 16:14 ` Marcelo Tosatti
2021-11-10 16:15 ` Jan Kiszka
2021-11-10 17:29 ` Marcelo Tosatti
2021-11-10 18:30 ` Waiman Long
2021-11-10 17:52 ` Michal Koutný
2021-11-10 18:04 ` Jan Kiszka
2021-11-10 18:15 ` Michal Koutný
2021-11-10 15:20 ` Waiman Long
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