Re: [PATCH 02/19] sched/fair: Record per-LLC utilization to guide cache-aware scheduling decisions

[Peter Zijlstra]

On Sat, Oct 11, 2025 at 11:24:39AM -0700, Tim Chen wrote:
> +static void record_sg_llc_stats(struct lb_env *env,
> +				struct sg_lb_stats *sgs,
> +				struct sched_group *group)
> +{
> +	/*
> +	 * Find the child domain on env->dst_cpu. This domain
> +	 * is either the domain that spans this group(if the
> +	 * group is a local group), or the sibling domain of
> +	 * this group.
> +	 */
> +	struct sched_domain *sd = env->sd->child;
> +	struct sched_domain_shared *sd_share;
> +
> +	if (!sched_feat(SCHED_CACHE) || env->idle == CPU_NEWLY_IDLE)
> +		return;
> +
> +	/* only care about sched domains spanning a LLC */
> +	if (sd != rcu_dereference(per_cpu(sd_llc, env->dst_cpu)))
> +		return;
> +
> +	/*
> +	 * At this point we know this group spans a LLC domain.
> +	 * Record the statistic of this group in its corresponding
> +	 * shared LLC domain.
> +	 */
> +	sd_share = rcu_dereference(per_cpu(sd_llc_shared,
> +					   cpumask_first(sched_group_span(group))));

Isn't this sd->shared ? Or did I loose the plot somewhere?

> +	if (!sd_share)
> +		return;
> +
> +	if (READ_ONCE(sd_share->util_avg) != sgs->group_util)
> +		WRITE_ONCE(sd_share->util_avg, sgs->group_util);
> +
> +	if (unlikely(READ_ONCE(sd_share->capacity) != sgs->group_capacity))
> +		WRITE_ONCE(sd_share->capacity, sgs->group_capacity);
> +}