[RFC PATCH 14/16] sched: Use energy model in select_idle_sibling

[Morten Rasmussen <morten.rasmussen@arm.com>]

Make select_idle_sibling() consider energy when picking an idle cpu.

Only idle cpus are still considered. A more aggressive energy conserving
approach could go further and consider partly utilized cpus.

Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
---
 kernel/sched/fair.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5a52467..542c2b2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4644,7 +4644,9 @@ static int select_idle_sibling(struct task_struct *p, int target)
 	struct sched_domain *sd;
 	struct sched_group *sg;
 	int i = task_cpu(p);
+	int target_energy;
 
+#ifndef CONFIG_SCHED_ENERGY
 	if (idle_cpu(target))
 		return target;
 
@@ -4653,6 +4655,8 @@ static int select_idle_sibling(struct task_struct *p, int target)
 	 */
 	if (i != target && cpus_share_cache(i, target) && idle_cpu(i))
 		return i;
+#endif
+	target_energy = energy_diff_task(target, p);
 
 	/*
 	 * Otherwise, iterate the domains and find an elegible idle cpu.
@@ -4666,8 +4670,12 @@ static int select_idle_sibling(struct task_struct *p, int target)
 				goto next;
 
 			for_each_cpu(i, sched_group_cpus(sg)) {
+				int diff;
 				if (i == target || !idle_cpu(i))
 					goto next;
+				diff = energy_diff_task(i, p);
+				if (diff > target_energy)
+					goto next;
 			}
 
 			target = cpumask_first_and(sched_group_cpus(sg),
-- 
1.7.9.5