On Fri, Nov 14, 2025 at 02:24:48PM +0800, Sun Shaojie sunshaojie@kylinos.cn 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.)
Thanks, Michal