Re: [PATCH v3 07/21] sched/cache: Introduce per CPU's tasks LLC preference counter

[Peter Zijlstra]

On Tue, Feb 10, 2026 at 02:18:47PM -0800, Tim Chen wrote:
> diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
> index a4e2fb31f2fd..3aa6c101b2e4 100644
> --- a/include/linux/sched/topology.h
> +++ b/include/linux/sched/topology.h
> @@ -102,6 +102,10 @@ struct sched_domain {
>  	u64 max_newidle_lb_cost;
>  	unsigned long last_decay_max_lb_cost;
>  
> +#ifdef CONFIG_SCHED_CACHE
> +	unsigned int *pf;

So I'm all for short names; but perhaps this could be better. When
reading this my brain went page-fault, and then WTF :-)

> +#endif
> +
>  #ifdef CONFIG_SCHEDSTATS
>  	/* sched_balance_rq() stats */
>  	unsigned int lb_count[CPU_MAX_IDLE_TYPES];

> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index ca46b5cf7f78..dae78b5915a7 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c

> @@ -2723,6 +2778,13 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
>  	}
>  	rcu_read_unlock();
>  
> +	/*
> +	 * Ensure we see enlarged sd->pf when we use new llc_ids and
> +	 * bigger max_llcs.
> +	 */
> +	smp_mb();
> +	max_llcs = tl_max_llcs;

This seems wrong. This is *after* cpu_attach_domain() which publishes
@sd. How about you do something like:

struct sched_domain {
	...

	unsigned int llc_max;
	unsigned int *llc_counts __counted_by(llc_max);
}

Then you always carry matching information that is published together.

>  	if (has_asym)
>  		static_branch_inc_cpuslocked(&sched_asym_cpucapacity);
>  
> -- 
> 2.32.0
>