Re: [PATCH 12/19] sched/fair: Add migrate_llc_task migration type for cache-aware balancing

[Tim Chen]

On Mon, 2025-10-27 at 14:34 +0530, K Prateek Nayak wrote:
> Hello Tim,
> 
> On 10/11/2025 11:54 PM, Tim Chen wrote:
> > @@ -12149,6 +12167,16 @@ static struct rq *sched_balance_find_src_rq(struct lb_env *env,
> >  			}
> >  			break;
> >  
> > +		case migrate_llc_task:
> > +#ifdef CONFIG_SCHED_CACHE
> > +			dst_llc = llc_idx(env->dst_cpu);
> > +			if (!cpus_share_cache(env->dst_cpu, rq->cpu) &&
> 
> Busiest group is always a non-local group right? Can cpus_share_cache()
> ever happen given we are looking at groups of first !SD_LLC_SHARE
> domain for "migrate_llc_task"?

That's a good point. We should have already checked that busiest
and local are not in the same LLC when we mark migrate_llc_task.
We shouldn't need to do cpus_share_cache() check here.

Tim


> 
> > +			    busiest_pref_llc < rq->nr_pref_llc[dst_llc]) {
> > +				busiest_pref_llc = rq->nr_pref_llc[dst_llc];
> > +				busiest = rq;
> > +			}
> > +#endif
> > +			break;
> >  		case migrate_task:
> >  			if (busiest_nr < nr_running) {
> >  				busiest_nr = nr_running;