linux-kernel - [PATCH 2/4] sched/fair: Defer calculation of prev_eff_load in wake

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Message-Id: <20180212145857.8056-3-mgorman@techsingularity.net>
Date:   Mon, 12 Feb 2018 14:58:55 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Mike Galbraith <efault@....de>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 2/4] sched/fair: Defer calculation of prev_eff_load in wake_affine until needed

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@...hsingularity.net>
---
 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 4b3e86eb2222..c1091cb023c4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5724,7 +5724,6 @@ 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);
@@ -5742,6 +5741,7 @@ 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;
-- 
2.15.1