Re: [RFC PATCH 3/5] sched/fair: Update overloaded mask in presence of pushable task

[K Prateek Nayak <kprateek.nayak@amd.com>]

Hello Shrikanth,

On 4/21/2025 1:33 PM, Shrikanth Hegde wrote:
>>> I was getting below error when compiling. Noticed that overloaded_mask is a local update and it wouldn't
>>> update the actual overloaded_mask.
>>
>> Interesting! Question: Do you have "CONFIG_CPUMASK_OFFSTACK" enabled in
>> your config? (me makes a note to test this too in the next iteration)
>> Looking at the arch specific Kconfigs, there is a slight difference in
>> how this is toggled on x86 vs powerpc and I'm wondering if that is why
>> I haven't seen this warning in my testing.
>>
> 
> Yes, that's the reason you didn't run into.
> for me, CONFIG_CPUMASK_OFFSTACK is not set.

Thank you for confirming!

> 
>>>
>>> Compilation Error:
>>> kernel/sched/fair.c: In function ‘update_overloaded_mask’:
>>> kernel/sched/fair.c:8570:25: error: assignment to expression with array type
>>>   8570 |         overloaded_mask = sd_share->overloaded_mask;
>>>        |                         ^
>>> kernel/sched/fair.c:8571:13: warning: the address of ‘overloaded_mask’ will always evaluate as ‘true’ [-Waddress]
>>>   8571 |         if (!overloaded_mask)
>>>
>>>
>>>
>>> Made the below change. Also you would need rcu protection for sd_share i think.
> 
> Or you need to use like below. This also works (Not tested on x86)
> 
> struct cpumask*  overloaded_mask;

Ack! Perhaps that is the way to go. I'll take some inspiration from
other cpumask usage in kernel and adjust this accordingly. Thanks a ton
for testing.

> 
>>
>> You are right! Thank you for the pointers and spotting my oversight.
>> Aaron too pointed some shortcomings here. I'll make sure to test
>> these bits more next time (LOCKDEP, hotplug, and
>> !CONFIG_CPUMASK_OFFSTACK)

-- 
Thanks and Regards,
Prateek