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

[Shrikanth Hegde]

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@xxxxxxxxxxxxx>
> > ---
> >   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