[RFCv3 PATCH 42/48] sched: Introduce energy awareness into find_busiest_queue

[Morten Rasmussen]

From: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>

In case that after the gathering of sched domain statistics the current
load balancing operation is still in energy-aware mode and a least
efficient sched group has been found, detect the least efficient cpu by
comparing the cpu efficiency (ratio between cpu usage and cpu energy
consumption) among all cpus of the least efficient sched group.

cc: Ingo Molnar <mingo@xxxxxxxxxx>
cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
---
 kernel/sched/fair.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 199ffff..48cd5b5 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7216,6 +7216,37 @@ static struct rq *find_busiest_queue(struct lb_env *env,
 	unsigned long busiest_load = 0, busiest_capacity = 1;
 	int i;
 
+	if (env->use_ea) {
+		struct rq *costliest = NULL;
+		unsigned long costliest_usage = 1024, costliest_energy = 1;
+
+		for_each_cpu_and(i, sched_group_cpus(group), env->cpus) {
+			unsigned long usage = get_cpu_usage(i);
+			struct rq *rq = cpu_rq(i);
+			struct sched_domain *sd = rcu_dereference(rq->sd);
+			struct energy_env eenv = {
+				.sg_top = sd->groups,
+				.usage_delta    = 0,
+				.src_cpu        = -1,
+				.dst_cpu        = -1,
+			};
+			unsigned long energy = sched_group_energy(&eenv);
+
+			/*
+			 * We're looking for the minimal cpu efficiency
+			 * min(u_i / e_i), crosswise multiplication leads to
+			 * u_i * e_j < u_j * e_i with j as previous minimum.
+			 */
+			if (usage * costliest_energy < costliest_usage * energy) {
+				costliest_usage = usage;
+				costliest_energy = energy;
+				costliest = rq;
+			}
+		}
+
+		return costliest;
+	}
+
 	for_each_cpu_and(i, sched_group_cpus(group), env->cpus) {
 		unsigned long capacity, wl;
 		enum fbq_type rt;
-- 
1.9.1

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