[Patch v4 13/22] sched/cache: Add migrate_llc_task migration type for cache-aware balancing

Tim Chen
2026-04-01T21:47:09Z

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.

Co-developed-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---

Notes:
v3->v4:
No change.

kernel/sched/fair.c | 38 +++++++++++++++++++++++++++++++++++++-
1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c032eeebe191..e0e618cd4e15 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9768,7 +9768,8 @@ enum migration_type {
migrate_load = 0,
migrate_util,
migrate_task,
- migrate_misfit
+ migrate_misfit,
+ migrate_llc_task
};

#define LBF_ALL_PINNED 0x01
@@ -10382,6 +10383,10 @@ static int detach_tasks(struct lb_env *env)

env->imbalance = 0;
break;
+
+ case migrate_llc_task:
+ env->imbalance--;
+ break;
}

detach_task(p, env);
@@ -12022,6 +12027,15 @@ 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
@@ -12328,7 +12342,10 @@ 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 __maybe_unused busiest_pref_llc = 0;
+ struct sched_domain __maybe_unused *sd_tmp;
unsigned int busiest_nr = 0;
+ int __maybe_unused dst_llc;
int i;

for_each_cpu_and(i, sched_group_span(group), env->cpus) {
@@ -12456,6 +12473,23 @@ static struct rq *sched_balance_find_src_rq(struct lb_env *env,

break;

+ case migrate_llc_task:
+#ifdef CONFIG_SCHED_CACHE
+ sd_tmp = rcu_dereference_all(rq->sd);
+ dst_llc = llc_id(env->dst_cpu);
+
+ if (valid_llc_buf(sd_tmp, dst_llc)) {
+ unsigned int this_pref_llc =
+ sd_tmp->llc_counts[dst_llc];
+
+ if (busiest_pref_llc < this_pref_llc) {
+ busiest_pref_llc = this_pref_llc;
+ busiest = rq;
+ }
+ }
+#endif
+ break;
+
}
}

@@ -12619,6 +12653,8 @@ 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