[RFCv3 PATCH 44/48] sched: Tipping point from energy-aware to conventional load balancing

[Morten Rasmussen]

From: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>

Energy-aware load balancing bases on cpu usage so the upper bound of its
operational range is a fully utilized cpu. Above this tipping point it
makes more sense to use weighted_cpuload to preserve smp_nice.
This patch implements the tipping point detection in update_sg_lb_stats
as if one cpu is over-utilized the current energy-aware load balance
operation will fall back into the conventional weighted load based one.

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

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
---
 kernel/sched/fair.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6b79603..4849bad 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6723,6 +6723,10 @@ static inline void update_sg_lb_stats(struct lb_env *env,
 		sgs->sum_weighted_load += weighted_cpuload(i);
 		if (idle_cpu(i))
 			sgs->idle_cpus++;
+
+		/* If cpu is over-utilized, bail out of ea */
+		if (env->use_ea && cpu_overutilized(i, env->sd))
+			env->use_ea = false;
 	}
 
 	/* Adjust by relative CPU capacity of the group */
-- 
1.9.1

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