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: <18ae1739-fe2f-4cd0-a7ea-35b908b42737@intel.com>
Date: Tue, 16 Dec 2025 08:52:52 +0800
From: "Chen, Yu C" <yu.c.chen@...el.com>
To: Peter Zijlstra <peterz@...radead.org>, 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>, 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 12/10/2025 9:32 PM, Peter Zijlstra wrote:
> 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!

OK, will fix the order.

Thanks,
Chenyu