[PATCH 08/14] sched: trig ILB on an idle buddy

[vincent.guittot@linaro.org (Vincent Guittot)]

If the buddy CPU is not full and currently idle, we trigger an Idle Load
Balance to give it the opportunity to pull more tasks.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
 kernel/sched/fair.c |   24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 874f330..954adfd 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5776,6 +5776,26 @@ end:
 	clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu));
 }
 
+static int check_nohz_buddy(int cpu)
+{
+	int buddy = per_cpu(sd_pack_buddy, cpu);
+
+	if (sysctl_sched_packing_mode != SCHED_PACKING_FULL)
+		return false;
+
+	/* No pack buddy for this CPU */
+	if (buddy == -1)
+		return false;
+
+	if (is_buddy_full(buddy))
+		return false;
+
+	if (cpumask_test_cpu(buddy, nohz.idle_cpus_mask))
+		return true;
+
+	return false;
+}
+
 /*
  * Current heuristic for kicking the idle load balancer in the presence
  * of an idle cpu is the system.
@@ -5813,6 +5833,10 @@ static inline int nohz_kick_needed(struct rq *rq, int cpu)
 	if (rq->nr_running >= 2)
 		goto need_kick;
 
+	/* the buddy is idle and not busy so we can pack */
+	if (check_nohz_buddy(cpu))
+		goto need_kick;
+
 	rcu_read_lock();
 	for_each_domain(cpu, sd) {
 		struct sched_group *sg = sd->groups;
-- 
1.7.9.5