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

[Tim Chen <tim.c.chen@linux.intel.com>]

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@linux.intel.com>
---
 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 8469ec528cb1..bec6354d7841 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9504,7 +9504,8 @@ enum migration_type {
 	migrate_load = 0,
 	migrate_util,
 	migrate_task,
-	migrate_misfit
+	migrate_misfit,
+	migrate_llc_task
 };
 
 #define LBF_ALL_PINNED	0x01
@@ -10082,6 +10083,10 @@ 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;
@@ -11733,6 +11738,15 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
 		return;
 	}
 
+#ifdef CONFIG_SCHED_CACHE
+	if (busiest->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
@@ -12041,6 +12055,10 @@ 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) {
@@ -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_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;
@@ -12331,6 +12359,8 @@ 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