Re: [PATCH 10/19] sched/fair: Prioritize tasks preferring destination LLC during balancing

[Aaron Lu]

Hi Tim,

On Sat, Oct 11, 2025 at 11:24:47AM -0700, Tim Chen wrote:
> @@ -10849,11 +10849,45 @@ static void record_sg_llc_stats(struct lb_env *env,
>  	if (unlikely(READ_ONCE(sd_share->capacity) != sgs->group_capacity))
>  		WRITE_ONCE(sd_share->capacity, sgs->group_capacity);
>  }
> +
> +/*
> + * Do LLC balance on sched group that contains LLC, and have tasks preferring
> + * to run on LLC in idle dst_cpu.
> + */
> +static inline bool llc_balance(struct lb_env *env, struct sg_lb_stats *sgs,
> +			       struct sched_group *group)
> +{
> +	struct sched_domain *child = env->sd->child;
> +	int llc;
> +
> +	if (!sched_cache_enabled())
> +		return false;
> +
> +	if (env->sd->flags & SD_SHARE_LLC)
> +		return false;
> +
> +	/* only care about task migration among LLCs */
> +	if (child && !(child->flags & SD_SHARE_LLC))
> +		return false;
> +
> +	llc = llc_idx(env->dst_cpu);
> +	if (sgs->nr_pref_llc[llc] > 0 &&
> +	    can_migrate_llc(env->src_cpu, env->dst_cpu, 0, true) == mig_llc)

llc_balance() is called from update_sg_lb_stats() and at that time,
env->src_cpu is not determined yet so should not be used here?

> +		return true;
> +
> +	return false;
> +}