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

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Message-ID: <4bc5ae54-4abb-426d-bcf9-708eeb6b34dd@amd.com>
Date: Mon, 27 Oct 2025 14:34:00 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Tim Chen <tim.c.chen@...ux.intel.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

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"?

> +			    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;

-- 
Thanks and Regards,
Prateek