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

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Message-ID: <0584faee6e0d5d7ca47c8ab5608caed3b9cb15dc.camel@linux.intel.com>
Date: Mon, 27 Oct 2025 15:59:27 -0700
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: K Prateek Nayak <kprateek.nayak@....com>, Peter Zijlstra	
 <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, "Gautham R .
 Shenoy"	 <gautham.shenoy@....com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>, Juri Lelli	
 <juri.lelli@...hat.com>, Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel
 Gorman <mgorman@...e.de>,  Valentin Schneider	 <vschneid@...hat.com>,
 Madadi Vineeth Reddy <vineethr@...ux.ibm.com>, Hillf Danton
 <hdanton@...a.com>, Shrikanth Hegde <sshegde@...ux.ibm.com>, Jianyong Wu	
 <jianyong.wu@...look.com>, Yangyu Chen <cyy@...self.name>, Tingyin Duan	
 <tingyin.duan@...il.com>, Vern Hao <vernhao@...cent.com>, Len Brown	
 <len.brown@...el.com>, Aubrey Li <aubrey.li@...el.com>, Zhao Liu	
 <zhao1.liu@...el.com>, Chen Yu <yu.chen.surf@...il.com>, Chen Yu	
 <yu.c.chen@...el.com>, Libo Chen <libo.chen@...cle.com>, Adam Li	
 <adamli@...amperecomputing.com>, Tim Chen <tim.c.chen@...el.com>, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 12/19] sched/fair: Add migrate_llc_task migration type
 for cache-aware balancing

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;