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

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Message-Id: <ab44d75ad69b81b669cbab41695c0e89407c6feb.1764801860.git.tim.c.chen@linux.intel.com>
Date: Wed,  3 Dec 2025 15:07:31 -0800
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	"Gautham R . Shenoy" <gautham.shenoy@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>
Cc: Tim Chen <tim.c.chen@...ux.intel.com>,
	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: [PATCH v2 12/23] sched/cache: Add migrate_llc_task migration type for cache-aware balancing

Introduce a new migration type, migrate_llc_task, to support
cache-aware load balancing.

After identifying the busiest sched_group (having the most tasks
preferring the destination LLC), mark migrations with this type.
During load balancing, each runqueue in the busiest sched_group is
examined, and the runqueue with the highest number of tasks preferring
the destination CPU is selected as the busiest runqueue.

Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
---

Notes:
    v1->v2: Remove unnecessary cpus_share_cache() check in
            sched_balance_find_src_rq() (K Prateek Nayak)

 kernel/sched/fair.c | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

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;
@@ -11766,6 +11771,15 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
 		return;
 	}
 
+#ifdef CONFIG_SCHED_CACHE
+	if (busiest->group_type == group_llc_balance) {
+		/* Move a task that prefer local LLC */
+		env->migration_type = migrate_llc_task;
+		env->imbalance = 1;
+		return;
+	}
+#endif
+
 	if (busiest->group_type == group_imbalanced) {
 		/*
 		 * In the group_imb case we cannot rely on group-wide averages
@@ -12073,6 +12087,10 @@ static struct rq *sched_balance_find_src_rq(struct lb_env *env,
 	struct rq *busiest = NULL, *rq;
 	unsigned long busiest_util = 0, busiest_load = 0, busiest_capacity = 1;
 	unsigned int busiest_nr = 0;
+#ifdef CONFIG_SCHED_CACHE
+	unsigned int busiest_pref_llc = 0;
+	int dst_llc;
+#endif
 	int i;
 
 	for_each_cpu_and(i, sched_group_span(group), env->cpus) {
@@ -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;
 	}
 }
 
-- 
2.32.0