Re: [PATCH v8 5/6] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst

[Waiman Long <longman@redhat.com>]

On 12/1/21 09:13, Michal Koutný wrote:
> On Tue, Nov 30, 2021 at 10:56:34PM -0500, Waiman Long <longman@redhat.com> wrote:
>>>>       A valid parent partition may distribute out all its CPUs to
>>>>       its child partitions as long as it is not the root cgroup and
>>>>       there is no task associated with it.
>>> A valid parent partition which isn't root never has tasks in them to begin
>>> with.
>> I believe there is some corner cases where it is possible to put task in an
>> intermediate partition. That is why I put down this statement.
> Just mind the threads -- cpuset controller is threaded and having tasks
> in inner cgroup nodes is a real scenario. I wouldn't consider it a
> corner case.
>
> [ Actually, the paragraph could IMO be simplified:
Right, I shouldn't say corner cases. Having task in an intermediate 
partition is possible depending on event sequence. I am aware that there 
are code in the cpuset code to prevent that, but it didn't block all cases.
>> A valid parent partition may distribute out all its CPUs to
>>   its child partitions as long as there is no task associated with it.
> Assuming there's always at least one kernel thread in the root cgroup
> that can't be migrated anyway.]

I am aware of that. That is why I said root cgroup must have at least 
one cpu in its "cpuset.cpus.effective".

Cheers,
Longman