[PATCH 1/1] sched: Consider CPU contention in frequency & load-balance busiest CPU selection

[Dietmar Eggemann]

Use new cpu_boosted_util_cfs() instead of cpu_util_cfs().

The former returns max(util_avg, runnable_avg) capped by max CPU
capacity. CPU contention is thereby considered through runnable_avg.

The change in load-balance only affects migration type `migrate_util`.

Suggested-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
---
 kernel/sched/cpufreq_schedutil.c |  3 ++-
 kernel/sched/fair.c              |  2 +-
 kernel/sched/sched.h             | 19 +++++++++++++++++++
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index e3211455b203..728b186cd367 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -158,7 +158,8 @@ static void sugov_get_util(struct sugov_cpu *sg_cpu)
 	struct rq *rq = cpu_rq(sg_cpu->cpu);
 
 	sg_cpu->bw_dl = cpu_bw_dl(rq);
-	sg_cpu->util = effective_cpu_util(sg_cpu->cpu, cpu_util_cfs(sg_cpu->cpu),
+	sg_cpu->util = effective_cpu_util(sg_cpu->cpu,
+					  cpu_boosted_util_cfs(sg_cpu->cpu),
 					  FREQUENCY_UTIL, NULL);
 }
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bc358dc4faeb..5ae36224a1c2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10481,7 +10481,7 @@ static struct rq *find_busiest_queue(struct lb_env *env,
 			break;
 
 		case migrate_util:
-			util = cpu_util_cfs(i);
+			util = cpu_boosted_util_cfs(i);
 
 			/*
 			 * Don't try to pull utilization from a CPU with one
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 060616944d7a..f42c859579d9 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2994,6 +2994,25 @@ static inline unsigned long cpu_util_cfs(int cpu)
 	return min(util, capacity_orig_of(cpu));
 }
 
+/*
+ * cpu_boosted_util_cfs() - Estimates the amount of CPU capacity used by
+ *                          CFS tasks.
+ *
+ * Similar to cpu_util_cfs() but also take possible CPU contention into
+ * consideration.
+ */
+static inline unsigned long cpu_boosted_util_cfs(int cpu)
+{
+	unsigned long runnable;
+	struct cfs_rq *cfs_rq;
+
+	cfs_rq = &cpu_rq(cpu)->cfs;
+	runnable = READ_ONCE(cfs_rq->avg.runnable_avg);
+	runnable = min(runnable, capacity_orig_of(cpu));
+
+	return max(cpu_util_cfs(cpu), runnable);
+}
+
 static inline unsigned long cpu_util_rt(struct rq *rq)
 {
 	return READ_ONCE(rq->avg_rt.util_avg);
-- 
2.25.1