Re: [PATCH v3] sched: Store restrict_cpus_allowed_ptr() call state

[Peter Zijlstra]

On Thu, Jan 26, 2023 at 08:55:27PM -0500, Waiman Long wrote:
> The user_cpus_ptr field was originally added by commit b90ca8badbd1
> ("sched: Introduce task_struct::user_cpus_ptr to track requested
> affinity"). It was used only by arm64 arch due to possible asymmetric
> CPU setup.
> 
> Since commit 8f9ea86fdf99 ("sched: Always preserve the user requested
> cpumask"), task_struct::user_cpus_ptr is repurposed to store user
> requested cpu affinity specified in the sched_setaffinity().
> 
> This results in a slight performance regression on an arm64
> system when booted with "allow_mismatched_32bit_el0"

Dude, how can you still call this a slight performance regression after
Will told you time and time again that's not the problem.

It clearly is a behavioural problem.