[tip:sched/core] sched/fair: Defer calculation of 'prev_eff_load' in wake_affine_weight() until needed

[tip-bot for Mel Gorman]

Commit-ID:  eeb60398639143c11ff2c8b509e3a471411bb5d3
Gitweb:     https://git.kernel.org/tip/eeb60398639143c11ff2c8b509e3a471411bb5d3
Author:     Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
AuthorDate: Tue, 13 Feb 2018 13:37:26 +0000
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 21 Feb 2018 08:49:07 +0100

sched/fair: Defer calculation of 'prev_eff_load' in wake_affine_weight() 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@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Giovanni Gherdovich <ggherdovich@xxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20180213133730.24064-3-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 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 0132572..ae3e6f8 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;