Re: [PATCH v4 03/20] kconfig: Provide PREFERRED_CPU option

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

Hi Yury, thanks for reviewing the patches.

On 6/18/26 6:21 AM, Yury Norov wrote:
> On Wed, Jun 17, 2026 at 11:11:22PM +0530, Shrikanth Hegde wrote:
>> Introduce a new config named PREFERRED_CPU.
>>
>> This helps to:
>> - Avoid the code bloat when PREFERRED_CPU=n. In that cases preferred
>>    is same as active.
>> - Avoid the ifdeffery around PREFERRED_CPU in many files.
>>
>> Since paravirtulized use case is the main driving force of this
>> feature, make it default for kernels with PARAVIRT=y
>>
>> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
>> ---
>>   kernel/Kconfig.preempt | 13 +++++++++++++
>>   1 file changed, 13 insertions(+)
>>
>> diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
>> index 88c594c6d7fc..0995f5ba66eb 100644
>> --- a/kernel/Kconfig.preempt
>> +++ b/kernel/Kconfig.preempt
>> @@ -192,3 +192,16 @@ config SCHED_CLASS_EXT
>>   	  For more information:
>>   	    Documentation/scheduler/sched-ext.rst
>>   	    https://github.com/sched-ext/scx
>> +
>> +config PREFERRED_CPU
>> +	bool "Dynamic vCPU management based on steal time"
>> +	default y if PARAVIRT && SMP
>> +	help
>> +	This feature helps to reduce the steal time in paravirtualised
>> +	environment, there by reducing vCPU preemption. Reducing vCPU
>> +	preemption provides improved lock holder preemption and reduces
>> +	cost of vCPU preemption in the host.
> 
> If it doesn't make sense for non-paravirt kernels, then
> 
>          depends on PARAVIRT && SMP
>          default y
> 

Ok.
Yes paravirt is the only use case today.

>> +
>> +	By default preferred CPUs will be same as active CPUs. Depending
>> +	on the steal time when steal monitor is enabled, preferred CPUs
>> +	could become subset of active CPUs.
>> -- 
>> 2.47.3