Re: [PATCH v3 09/20] sched/rt: Select a preferred CPU for wakeup and pulling rt task

[Peter Zijlstra <peterz@infradead.org>]

On Thu, May 14, 2026 at 08:51:53PM +0530, Shrikanth Hegde wrote:
> For RT class,
> - During wakeup choose a preferred CPU.
> - For push_rt framework, limit pushing to preferred CPUs
> - Pull the rt task only if CPU is preferred.

So this one might have the potential to break things. Preferring a
preferred cpu, sure, but to the exclusion of active, perhaps not.

Also, where are the DL changes?

> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> ---
>  kernel/sched/cpupri.c | 1 +
>  kernel/sched/rt.c     | 4 ++++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/kernel/sched/cpupri.c b/kernel/sched/cpupri.c
> index 8f2237e8b484..24eb26ea9a91 100644
> --- a/kernel/sched/cpupri.c
> +++ b/kernel/sched/cpupri.c
> @@ -103,6 +103,7 @@ static inline int __cpupri_find(struct cpupri *cp, struct task_struct *p,
>  	if (lowest_mask) {
>  		cpumask_and(lowest_mask, &p->cpus_mask, vec->mask);
>  		cpumask_and(lowest_mask, lowest_mask, cpu_active_mask);
> +		cpumask_and(lowest_mask, lowest_mask, cpu_preferred_mask);
>  
>  		/*
>  		 * We have to ensure that we have at least one bit
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 4ee8faf01441..62c53f10de24 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -2262,6 +2262,10 @@ static void pull_rt_task(struct rq *this_rq)
>  	if (likely(!rt_overload_count))
>  		return;
>  
> +	/* No point in pulling the load, just to push it next tick again */
> +	if (!cpu_preferred(this_cpu))
> +		return;
> +
>  	/*
>  	 * Match the barrier from rt_set_overloaded; this guarantees that if we
>  	 * see overloaded we must also see the rto_mask bit.
> -- 
> 2.47.3
>