Re: [QUESTION/REGRESSION] Unbound kthreads scheduled on nohz_full CPUs after commit 041ee6f3727a

[sheviks]

Frederic Weisbecker <frederic@xxxxxxxxxx> 於 2026年3月24日週二 上午5:32寫道：
> "ps -o cpuid" tells where the task is currently running or, if sleeping, where
> it ran last.
>
> The cpuids that belong to isolated CPUs you're observing on some kthreads are there
> because those tasks have slept the whole time since the cpuset isolated
> partition was created. Yet they have been correctly migrated to CPU 0 and that
> will be displayed on "ps -o cpuid" the next time those kthreads are woken up.
>
> Use taskset for more accurate information as to where a task is allowed to run.
>

Thank you very much for the clarification regarding ps vs taskset.

I have re-tested the system using taskset as you suggested.
I can confirm that the affinity masks are indeed updated correctly and
immediately across all kthreads as soon as the cgroup v2 isolated
partition is toggled.

My previous observation was indeed misled by the "last ran CPU" shown
in ps while the threads were sleeping.
This perfectly clears up my confusion.
I appreciate you taking the time to explain this technical nuance!

Best regards,
Sheviks