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

[Chen, Yu C]

Hi Aaron,

On 10/24/2025 5:32 PM, Aaron Lu wrote:
> 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?

You are right, I think we should check the candidate group's first
CPU rather than the env->src_cpu. Will fix it in the next version.
Thanks a lot!

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