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From: "Michal Koutný" <firstname.lastname@example.org>
To: Waiman Long <email@example.com>
Cc: Tejun Heo <firstname.lastname@example.org>, Zefan Li <email@example.com>,
Johannes Weiner <firstname.lastname@example.org>,
Jonathan Corbet <email@example.com>, Shuah Khan <firstname.lastname@example.org>,
Andrew Morton <email@example.com>,
Roman Gushchin <firstname.lastname@example.org>, Phil Auld <email@example.com>,
Peter Zijlstra <firstname.lastname@example.org>,
Juri Lelli <email@example.com>,
Frederic Weisbecker <firstname.lastname@example.org>,
Marcelo Tosatti <email@example.com>
Subject: Re: [PATCH v7 5/6] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst
Date: Mon, 30 Aug 2021 19:59:43 +0200 [thread overview]
Message-ID: <YS0cj+0thCHmXw/M@blackbook> (raw)
On Fri, Aug 27, 2021 at 06:50:10PM -0400, Waiman Long <firstname.lastname@example.org> wrote:
> So the new rules will be:
When I followed the thread, it seemed to me you're talking past each
other a bit. I'd suggest the following terminology:
- config space: what's written by the user and saved,
- reality space: what's currently available (primarily subject to
on-/offlinng but I think it'd be helpful to consider here also what's
given by the parent),
- effect space: what's actually possible and happening.
Not all elements of config_space x reality_space (Cartesian product) can
be represented in the effect_space (e.g. root partition with no
IIUC, Waiman's "high bar" is supposed to be defined over transitions in
the config_space. However, there can be independent changes in the
reality_space so the rules should be actually formulated in the
The conditions for being a valid partition root rewritten into the effect
> 1) The "cpuset.cpus" is not empty and the list of CPUs are exclusive.
- effective CPUs are non-empty and exclusive wrt siblings
- (E.g. setting empty cpuset.cpus might be possible but it invalidates
the partition root, same as offlining or removal by an ancestor.)
> 2) The parent cgroup is a partition root (can be an invalid one).
- parent cgroup is a (valid) partition
- (Being valid partition means owning "stolen" cpus from the parent, if
the parent is not valid partition itself, you can't steal what is not
- (And I think it's OK that: "the child partitions will stay invalid
forever unless the parent become a valid partition again" .)
> 3) The "cpuset.cpus" is a subset of the parent's cpuset.cpus.allowed.
- I'm not sure what is the use of this condition (together with the
rewrite of the 1st condition which covers effective cpus). I think it
would make sense if being a valid parition root guaranteed that all
configured cpuset.cpus will be available, however, that's not the case
IIUC (e.g. due to offlining).
> 4) No child cgroup with cpuset enabled.
- A child cgroup with cpuset enabled is OK in the effect space
(achievable by switching first and creating children later).
- For technical reasons this may be a condition on the transitions in
Generally, most config changes should succeed and user should check (or
watch) how they landed in combination with the reality_space.
 This follows the general model where ancestors can "preempt"
resources from their subtree.
next prev parent reply other threads:[~2021-08-30 17:59 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-25 21:37 [PATCH v7 0/6] cgroup/cpuset: Add new cpuset partition type & empty effecitve cpus Waiman Long
2021-08-25 21:37 ` [PATCH v7 1/6] cgroup/cpuset: Properly transition to invalid partition Waiman Long
2021-08-25 21:37 ` [PATCH v7 2/6] cgroup/cpuset: Show invalid partition reason string Waiman Long
2021-08-25 21:37 ` [PATCH v7 3/6] cgroup/cpuset: Add a new isolated cpus.partition type Waiman Long
2021-08-25 21:37 ` [PATCH v7 4/6] cgroup/cpuset: Allow non-top parent partition to distribute out all CPUs Waiman Long
2021-08-25 21:37 ` [PATCH v7 5/6] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst Waiman Long
2021-08-26 17:35 ` Tejun Heo
2021-08-27 3:01 ` Waiman Long
2021-08-27 4:00 ` Tejun Heo
2021-08-27 21:19 ` Waiman Long
2021-08-27 21:27 ` Tejun Heo
2021-08-27 22:50 ` Waiman Long
2021-08-27 23:35 ` Tejun Heo
2021-08-28 1:14 ` Waiman Long
[not found] ` <email@example.com>
2021-10-12 14:39 ` Michal Koutný
2021-10-13 21:45 ` Waiman Long
2021-10-13 22:11 ` Waiman Long
2021-08-30 17:59 ` Michal Koutný [this message]
2021-08-25 21:37 ` [PATCH v7 6/6] kselftest/cgroup: Add cpuset v2 partition root state test Waiman Long
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