From 8246e7280992a0f605c53518b25f1e2095c7bb90 Mon Sep 17 00:00:00 2001
From: Mel Gorman <mgorman@suse.de>
Date: Tue, 6 Feb 2018 22:25:01 +0000
Subject: [PATCH] sched/fair: Defer calculation of prev_eff_load in wake_affine
 until needed

References: bnc#1064414
Patch-mainline: No, received positive review and expected in v4.17

On sync wakeups, the previous CPU effective load may not be used so delay
the calculation until it's needed.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9037f3c4669d..a7ddf519b600 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5743,7 +5743,6 @@ wake_affine_weight(struct sched_domain *sd, struct task_struct *p,
 	unsigned long task_load;
 
 	this_eff_load = target_load(this_cpu, sd->wake_idx);
-	prev_eff_load = source_load(prev_cpu, sd->wake_idx);
 
 	if (sync) {
 		unsigned long current_load = task_h_load(current);
@@ -5761,6 +5760,7 @@ wake_affine_weight(struct sched_domain *sd, struct task_struct *p,
 		this_eff_load *= 100;
 	this_eff_load *= capacity_of(prev_cpu);
 
+	prev_eff_load = source_load(prev_cpu, sd->wake_idx);
 	prev_eff_load -= task_load;
 	if (sched_feat(WA_BIAS))
 		prev_eff_load *= 100 + (sd->imbalance_pct - 100) / 2;