Re: [PATCH v14 04/13] cpumask: Introduce cpu_preferred_mask

[Mete Durlu <meted@linux.ibm.com>]

On 28/09/2026 07:37, Shrikanth Hegde wrote:
> Provide the preferred CPU infrastructure. Define get/set macros
> which could be used to get/set CPU state as preferred.
> 
> CONFIG_PREFERRED_CPU will be selected by the driver which handles
> steal time values. It is going to set/clear preferred CPU state.
> This driver will be called steal_governor and it is introduced in
> subsequent patches. It periodically computes the steal ratio and
> decides on preferred CPU state.
> 
> A CPU is set to preferred when it becomes active. Later it may be
> marked as non-preferred depending on steal ratio by the steal_governor.
> 
> Always maintain design construct of preferred is subset of active.
> i.e. preferred ⊆ active ⊆ online ⊆ present ⊆ possible
> 
> With CONFIG_PREFERRED_CPU=n, ensure set_cpu_preferred is a nop and get
> method returns the active state in that case.
> 
> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> ---
>   include/linux/cpumask.h | 24 ++++++++++++++++++++++++
>   kernel/Kconfig.preempt  |  4 ++++
>   kernel/cpu.c            |  6 ++++++
>   kernel/sched/core.c     |  5 +++++
>   4 files changed, 39 insertions(+)

[..snip..]

>   
>   #define cpu_is_offline(cpu)	unlikely(!cpu_online(cpu))
> diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
> index 985aea617cfe..edc067a0c422 100644
> --- a/kernel/Kconfig.preempt
> +++ b/kernel/Kconfig.preempt
> @@ -194,3 +194,7 @@ config SCHED_CLASS_EXT
>   	  For more information:
>   	    Documentation/scheduler/sched-ext.rst
>   	    https://github.com/sched-ext/scx
> +
> +config PREFERRED_CPU
> +	bool
> +	depends on SMP && PARAVIRT
FWICT, PREFERRED_CPU mechanism can work perfectly fine without PARAVIRT
selected. It would be annoying to enable it and implement a dummy
paravirt_steal_clock() just for that.

Shrikanth, would it be possible to drop that dependency?

Thanks!
-Mete