Hi, Longman, On Mon, 24 Nov 2025 17:30:47, Waiman Long wrote: >On 11/19/25 5:57 AM, Sun Shaojie 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 >> >> 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". >> >> All other cases remain unaffected. For example, cgroup-v1. > >This patch is relatively simple. As others have pointed out, there are >inconsistency depending on the operation ordering. > >In the example above, the final configuration is A1:0-1 & B1:1-2. As the >cpu lists overlap, we can't have both of them as valid partition roots. >So either one of A1 or B1 is valid or they are both invalid. The current >code makes them both invalid no matter the operation ordering. This >patch will make one of them valid given the operation ordering above. To >minimize partition invalidation, we will have to live with the fact that >it will be first-come first-serve as noted by Michal. I am not against >this, we just have to document it. However, the following operation >order will still make both of them invalid: > ># echo "0-1" >A1/cpuset.cpus # echo "2" > B1/cpuset.cpus # echo "1-2" > >B1/cpuset.cpus # echo "root" > A1/cpuset.cpus.partition # echo "root" > >B1/cpuset.cpus.partition > >To follow the "first-come first-serve" rule, A1 should be valid and B1 >invalid. That is the inconsistency with your current patch. To fix that, >we still need to relax the overlap checking rule similar to your v4 patch.
Thank you for your suggestion! Will update. Thanks, Sun Shaojie
