On 2025/12/1 17:44, Sun Shaojie wrote:
> Hi, Ridong,
>
> On Thu, 27 Nov 2025 09:55:21, Chen Ridong wrote:
>> I have to admit that I prefer the current implementation.
>>
>> At the very least, it ensures that all partitions are treated fairly[1].
>> Relaxing this rule would
>> make it more difficult for users to understand why the cpuset.cpus they
>> configured do not match the
>> effective CPUs in use, and why different operation orders yield different
>> results.
>
> As for "different operation orders yield different results", Below is an
> example that is not a corner case.
>
> root cgroup
> / \
> A1 B1
>
> #1> echo "0" > A1/cpuset.cpus
> #2> echo "0-1" > B1/cpuset.cpus.exclusive --> return error
>
> #1> echo "0-1" > B1/cpuset.cpus.exclusive
> #2> echo "0" > A1/cpuset.cpus
>
You're looking at one rule, but there's another one—Longman pointed out that
setting cpuset.cpu
should never fail.
>>
>> In another scenario, if we do not invalidate the siblings, new leaf cpusets
>> (marked as member)
>> created under A1 will end up with empty effective CPUs—and this is not a
>> desired behavior.
>>
>> root cgroup
>> |
>> A1
>> / \
>> A2 A3...
>>
>> #1> echo "0-1" > A1/cpuset.cpus
>> #2> echo "root" > A1/cpuset.cpus.partition
>> #3> echo "0-1" > A2/cpuset.cpus
>> #4> echo "root" > A2/cpuset.cpus.partition
>> mkdir A4
>> mkdir A5
>> echo "0" > A4/cpuset.cpus
>> echo $$ > A4/cgroup.procs
>> echo "1" > A5/cpuset.cpus
>> echo $$ > A5/cgroup.procs
>>
>
> If A2...A5 all belong to the same user, and that user wants both A4 and A5
> to have effective CPUs, then the user should also understand that A2 needs
> to be adjusted to "member" instead of "root".
>
> if A2...A5 belong to different users, must satisfying user A4’s requirement
> come at the expense of user A2’s requirement? That is not fair.
>
Regarding cpuset usage with Docker: when binding CPUs at container startup, do
you check the sibling
CPUs in use? Without this check, A2 will not be invalidated.
Your patch has been discussed for a while. It seems to make the rules more
complex.
>>
>> [1]: "B1 is a second-class partition only because it starts later or why is
>> it OK to not fulfill its
>> requirement?" --Michal.
>
> Thanks,
> Sun Shaojie
--
Best regards,
Ridong
