linux-kernel - Re: [PATCH v2 12/23] sched/cache: Add migrate_llc_task migration type for cache-aware balancing

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Message-ID: <20251210133252.GU3707891@noisy.programming.kicks-ass.net>
Date: Wed, 10 Dec 2025 14:32:52 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Tim Chen <tim.c.chen@...ux.intel.com>
Cc: Ingo Molnar <mingo@...hat.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	"Gautham R . Shenoy" <gautham.shenoy@....com>,
	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>, Vern Hao <haoxing990@...il.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>,
	Adam Li <adamli@...amperecomputing.com>,
	Aaron Lu <ziqianlu@...edance.com>, Tim Chen <tim.c.chen@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 12/23] sched/cache: Add migrate_llc_task migration
 type for cache-aware balancing

On Wed, Dec 03, 2025 at 03:07:31PM -0800, Tim Chen wrote:
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index db555c11b5b8..529adf342ce0 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9547,7 +9547,8 @@ enum migration_type {
>  	migrate_load = 0,
>  	migrate_util,
>  	migrate_task,
> -	migrate_misfit
> +	migrate_misfit,
> +	migrate_llc_task
>  };
>  
>  #define LBF_ALL_PINNED	0x01
> @@ -10134,6 +10135,10 @@ static int detach_tasks(struct lb_env *env)
>  			env->imbalance -= util;
>  			break;
>  
> +		case migrate_llc_task:
> +			env->imbalance--;
> +			break;
> +
>  		case migrate_task:
>  			env->imbalance--;
>  			break;

> @@ -12181,6 +12199,16 @@ static struct rq *sched_balance_find_src_rq(struct lb_env *env,
>  			}
>  			break;
>  
> +		case migrate_llc_task:
> +#ifdef CONFIG_SCHED_CACHE
> +			dst_llc = llc_id(env->dst_cpu);
> +			if (dst_llc >= 0 &&
> +			    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;
> @@ -12363,6 +12391,8 @@ static void update_lb_imbalance_stat(struct lb_env *env, struct sched_domain *sd
>  	case migrate_misfit:
>  		__schedstat_add(sd->lb_imbalance_misfit[idle], env->imbalance);
>  		break;
> +	case migrate_llc_task:
> +		break;
>  	}
>  }

The enum and all switch statements had the same order; you wrecked it!