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

Waiman Long
2023-01-30T19:06:31Z

On 1/30/23 06:56, Peter Zijlstra wrote:
> 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.

I am trying to figure out if this behavioral problem is a result of my
scheduler patch or just as a result of cgroup v1 current behavior as I
don't see how my patch will cause this behavioral change if it is not an
existing problem.

Cheers,
Longman