[RFC PATCH v3 5/6] sched: pack the idle load balance

[Vincent Guittot <vincent.guittot@linaro.org>]

Look for an idle CPU close to the pack buddy CPU whenever possible.
The goal is to prevent the wake up of a CPU which doesn't share the power
domain of the pack buddy CPU.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Morten Rasmussen <morten.rasmussen@arm.com>
---
 kernel/sched/fair.c |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b636199..52a7736 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5455,7 +5455,25 @@ static struct {
 
 static inline int find_new_ilb(int call_cpu)
 {
+	struct sched_domain *sd;
 	int ilb = cpumask_first(nohz.idle_cpus_mask);
+	int buddy = per_cpu(sd_pack_buddy, call_cpu);
+
+	/*
+	 * If we have a pack buddy CPU, we try to run load balance on a CPU
+	 * that is close to the buddy.
+	 */
+	if (buddy != -1)
+		for_each_domain(buddy, sd) {
+			if (sd->flags & SD_SHARE_CPUPOWER)
+				continue;
+
+			ilb = cpumask_first_and(sched_domain_span(sd),
+					nohz.idle_cpus_mask);
+
+			if (ilb < nr_cpu_ids)
+				break;
+		}
 
 	if (ilb < nr_cpu_ids && idle_cpu(ilb))
 		return ilb;
-- 
1.7.9.5