On 2025/11/19 21:20, Michal Koutný wrote:
On Wed, Nov 19, 2025 at 06:57:49PM +0800, Sun Shaojie sunshaojie@kylinos.cn wrote:
Currently, when setting a cpuset's cpuset.cpus to a value that conflicts with its sibling partition, the sibling's partition state becomes invalid. However, this invalidation is often unnecessary. If the cpuset being modified is exclusive, it should invalidate itself upon conflict.
This patch applies only to the following two cases：
Assume the machine has 4 CPUs (0-3).
root cgroup / \ A1 B1
Case 1: A1 is exclusive, B1 is non-exclusive, set B1's cpuset.cpus
Table 1.1: Before applying this patch Step | A1's prstate | B1's prstate | #1> echo "0-1" > A1/cpuset.cpus | member | member | #2> echo "root" > A1/cpuset.cpus.partition | root | member | #3> echo "0" > B1/cpuset.cpus | root invalid | member |
After step #3, A1 changes from "root" to "root invalid" because its CPUs (0-1) overlap with those requested by B1 (0). However, B1 can actually use CPUs 2-3(from B1's parent), so it would be more reasonable for A1 to remain as "root."
Table 1.2: After applying this patch Step | A1's prstate | B1's prstate | #1> echo "0-1" > A1/cpuset.cpus | member | member | #2> echo "root" > A1/cpuset.cpus.partition | root | member | #3> echo "0" > B1/cpuset.cpus | root | member |
Case 2: Both A1 and B1 are exclusive, set B1's cpuset.cpus
(Thanks for working this out, Shaojie.)
Table 2.1: Before applying this patch Step | A1's prstate | B1's prstate | #1> echo "0-1" > A1/cpuset.cpus | member | member | #2> echo "root" > A1/cpuset.cpus.partition | root | member | #3> echo "2" > B1/cpuset.cpus | root | member | #4> echo "root" > B1/cpuset.cpus.partition | root | root | #5> echo "1-2" > B1/cpuset.cpus | root invalid | root invalid |
After step #4, B1 can exclusively use CPU 2. Therefore, at step #5, regardless of what conflicting value B1 writes to cpuset.cpus, it will always have at least CPU 2 available. This makes it unnecessary to mark A1 as "root invalid".
Table 2.2: After applying this patch Step | A1's prstate | B1's prstate | #1> echo "0-1" > A1/cpuset.cpus | member | member | #2> echo "root" > A1/cpuset.cpus.partition | root | member | #3> echo "2" > B1/cpuset.cpus | root | member | #4> echo "root" > B1/cpuset.cpus.partition | root | root | #5> echo "1-2" > B1/cpuset.cpus | root | root invalid |
In summary, regardless of how B1 configures its cpuset.cpus, there will always be available CPUs in B1's cpuset.cpus.effective. Therefore, there is no need to change A1 from "root" to "root invalid".
Admittedly, I don't like this change because it relies on implicit preference ordering between siblings (here first comes, first served)
Agree. If we only invalidate the latter one, I think regardless of the implementation approach, we may end up with different results depending on the order of operations.
and so the effective config cannot be derived just from the applied values :-/
Do you actually want to achieve this or is it an implementation side-effect of the Case 1 scenario that you want to achieve?
Thanks, Michal