On Wed, Nov 19, 2025 at 06:57:49PM +0800, Sun Shaojie <[email protected]> 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) 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
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