Re: [PATCH v13 06/13] sched/core: Try to use a preferred CPU in is_cpu_allowed

[Peter Zijlstra]

On Wed, Sep 09, 2026 at 07:26:10PM +0530, Shrikanth Hegde wrote:

> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index a689a0cea4eb..b4ef2e92d786 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2504,6 +2504,23 @@ static inline bool rq_has_pinned_tasks(struct rq *rq)
>  	return rq->nr_pinned;
>  }
>  
> +static inline bool task_can_sched_on_preferred(int cpu, struct task_struct *p)

(somehow those arguments feel backwards)

> +{
> +	if (cpu_preferred(cpu))
> +		return false;

FWIW, this reads very weird. task_can_sched_on_preferred() returning
false when task is on a preferred cpu.

The question really is more like: can we migrate to a preferred CPU, and
in that context it makes more sense. No point in migrating if we are
already on one.

Perhaps a comment on top of the function can clarify?

> +	/* Only FAIR tasks honor preferred CPU state */
> +	if (unlikely(p->sched_class != &fair_sched_class))
> +		return false;
> +
> +	/* Ignore preferred state if task affinity is changing */
> +	if (unlikely(!cpumask_test_cpu(task_cpu(p), p->cpus_ptr)))
> +		return false;
> +
> +	return cpumask_intersects_and(p->cpus_ptr, cpu_preferred_mask,
> +				      task_cpu_possible_mask(p));
> +}