On 2025/11/15 0:15, Michal Koutný wrote:
> On Fri, Nov 14, 2025 at 02:24:48PM +0800, Sun Shaojie <[email protected]>
> wrote:
>> The desired outcome is that after step #5, although B1 writes "0-3" to
>> cpuset.cpus, A1 can still remain as "root", and B1 ends up with effective
>> CPUs of 2-3. In summary, We want to avoid A1's invalidation when B1
>> changes its cpuset.cpus. Because cgroup v2 allows the effective CPU mask
>> of a cpuset to differ from its requested mask.
>
> So the new list of reasons why configured cpuset's cpus change are:
> - hotplug,
> - ancestor's config change,
> - stealing by a sibling (new).
>
> IIUC, the patch proposes this behavior:
>
> echo root >A1.cpuset.partition
> echo 0-1 >A1.cpuset.cpus
>
> echo root >B1.cpuset.partition
> echo 1-2 >B1.cpuset.cpus # invalidates A1
>
> echo 0-1 >A1.cpuset.cpus # invalidates B1
>
> ping-pong over CPU 1 ad libitum
>
> I think the right (tm) behavior would be not to depend on the order in
> which config is applied to siblings, i.e.
>
> echo root >A1.cpuset.partition
> echo 0-1 >A1.cpuset.cpus
>
> echo root >B1.cpuset.partition
> echo 1-2 >B1.cpuset.cpus # invalidates both A1 and B1
>
> echo 0-1 >A1.cpuset.cpus # no change anymore
>
> (I hope my example sheds some light on my understanding of the situation
> and desired behavior.)
Before applying the patch, the behavior I got:
# cd /sys/fs/cgroup/
# mkdir A1
# mkdir B1
# echo root > A1/cpuset.cpus.partition
# echo 0-1 > A1/cpuset.cpus
# cat A1/cpuset.cpus.partition
root
# echo root > B1/cpuset.cpus.partition
# echo 1-2 > B1/cpuset.cpus # A1 is exclusive, invalidate both A1 and
B1
# cat A1/cpuset.cpus.partition
root invalid
# cat B1/cpuset.cpus.partition
root invalid (cpuset.cpus and cpuset.cpus.exclusive are empty)
# echo root > B1/cpuset.cpus.partition
# cat B1/cpuset.cpus.partition
root invalid (Cpu list in cpuset.cpus not exclusive)
# echo root > A1/cpuset.cpus.partition
# cat A1/cpuset.cpus.partition
root invalid (Cpu list in cpuset.cpus not exclusive)
#
After applying the patch, the behavior I got:
# cd /sys/fs/cgroup/
# mkdir A1
# mkdir B1
# echo root > A1/cpuset.cpus.partition
# echo 0-1 > A1/cpuset.cpus
# cat A1/cpuset.cpus.partition
root
# echo root > B1/cpuset.cpus.partition
# echo 1-2 > B1/cpuset.cpus # A1 is exclusive, B1 is going to be
exclusive
# cat A1/cpuset.cpus.partition
root
# cat B1/cpuset.cpus.partition # A1 and B1 should be invalid.
root
# echo member > B1/cpuset.cpus.partition
# echo root > B1/cpuset.cpus.partition
# cat A1/cpuset.cpus.partition
root
# cat B1/cpuset.cpus.partition
root invalid (Cpu list in cpuset.cpus not exclusive)
# echo member > A1/cpuset.cpus.partition
# echo root > B1/cpuset.cpus.partition
# echo root > A1/cpuset.cpus.partition
# cat A1/cpuset.cpus.partition
root invalid (Cpu list in cpuset.cpus not exclusive)
# cat B1/cpuset.cpus.partition
root
After applying the patch, The result is unexpected.
--
Best regards,
Ridong
