Re: [PATCH v5 04/24] cpumask: Introduce cpu_preferred_mask

[Shrikanth Hegde <sshegde@linux.ibm.com>]

On 6/26/26 6:48 PM, Yury Norov wrote:
> On Fri, Jun 26, 2026 at 06:39:48PM +0530, Shrikanth Hegde wrote:
>> Hi Peter, Yury.
>>
>> On 6/26/26 3:11 PM, Peter Zijlstra wrote:
>>> On Fri, Jun 26, 2026 at 11:39:01AM +0200, Peter Zijlstra wrote:
>>>> On Thu, Jun 25, 2026 at 06:16:28PM +0530, Shrikanth Hegde wrote:
>>>>
>>>>> diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
>>>>> index 80211900f373..5a643d608ea6 100644
>>>>> --- a/include/linux/cpumask.h
>>>>> +++ b/include/linux/cpumask.h
>>>>> @@ -120,12 +120,20 @@ extern struct cpumask __cpu_enabled_mask;
>>>>>    extern struct cpumask __cpu_present_mask;
>>>>>    extern struct cpumask __cpu_active_mask;
>>>>>    extern struct cpumask __cpu_dying_mask;
>>>>> +
>>>>> +#ifdef CONFIG_PREFERRED_CPU
>>>>> +extern struct cpumask __cpu_preferred_mask;
>>>>> +#else
>>>>> +#define __cpu_preferred_mask __cpu_active_mask
>>>>> +#endif
>>>>
>>>> This is cure, but does it not result in set_cpu_preferred() changing
>>> s/cure/cute/
>>>> active mask, and it that not somewhat unexpected behaviour?
>>> s/it/is/
>>>
>>
>> Yes. I thought about this, but i didn't see anything bad happening apart from
>> setting it twice. But I do agree, it is an eyesore when CONFIG_PREFERRED_CPU=n.
>>
>>> Typing hard, clearly. Also hitting 30C before noon :-(
>>>
>>
>> Take care. Even we should have had monsoon by now.
>> But its bright sunshine :(
>>
>>>
>>
>> For this reason, i had it as a function instead of macro in v4.
>> Do you think we can still fallback to it?
>>
>> only caveat is it won't be a macro. But since it is still compile
>> time optimized due to IS_ENABLED, it should be relatively ok right?
>>
>> +void set_cpu_preferred(unsigned int cpu, bool preferred)
>> +{
>> +	if (!IS_ENABLED(CONFIG_PREFERRED_CPU))
>> +		return;
>> +
>> +	assign_cpu((cpu), &__cpu_preferred_mask, (preferred));
>> +}
> 
>   #ifdef CONFIG_PREFERRED_CPU
>   #define set_cpu_preferred(cpu, preferred) assign_cpu((cpu), &__cpu_preferred_mask, (preferred))
>   #else
>   #define set_cpu_preferred(cpu, preferred) {}
>   #endif
> 

Ah! thanks.