[tip:sched/core] sched/fair: Defer calling scaling functions

[tip-bot for Dietmar Eggemann]

Commit-ID:  6f2b04524f0b38bfbb8413f98d2d6af234508309
Gitweb:     http://git.kernel.org/tip/6f2b04524f0b38bfbb8413f98d2d6af234508309
Author:     Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
AuthorDate: Mon, 7 Sep 2015 14:57:22 +0100
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Sun, 13 Sep 2015 09:53:01 +0200

sched/fair: Defer calling scaling functions

Do not call the scaling functions in case time goes backwards or the
last update of the sched_avg structure has happened less than 1024ns
ago.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Juri Lelli <Juri.Lelli@xxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: daniel.lezcano@xxxxxxxxxx <daniel.lezcano@xxxxxxxxxx>
Cc: mturquette@xxxxxxxxxxxx <mturquette@xxxxxxxxxxxx>
Cc: pang.xunlei@xxxxxxxxxx <pang.xunlei@xxxxxxxxxx>
Cc: rjw@xxxxxxxxxxxxx <rjw@xxxxxxxxxxxxx>
Cc: sgurrappadi@xxxxxxxxxx <sgurrappadi@xxxxxxxxxx>
Cc: vincent.guittot@xxxxxxxxxx <vincent.guittot@xxxxxxxxxx>
Cc: yuyang.du@xxxxxxxxx <yuyang.du@xxxxxxxxx>
Link: http://lkml.kernel.org/r/55EDA2E9.8040900@xxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/sched/fair.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c3c5585..fc835fa 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2552,8 +2552,7 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa,
 	u64 delta, scaled_delta, periods;
 	u32 contrib;
 	unsigned int delta_w, scaled_delta_w, decayed = 0;
-	unsigned long scale_freq = arch_scale_freq_capacity(NULL, cpu);
-	unsigned long scale_cpu = arch_scale_cpu_capacity(NULL, cpu);
+	unsigned long scale_freq, scale_cpu;
 
 	delta = now - sa->last_update_time;
 	/*
@@ -2574,6 +2573,9 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa,
 		return 0;
 	sa->last_update_time = now;
 
+	scale_freq = arch_scale_freq_capacity(NULL, cpu);
+	scale_cpu = arch_scale_cpu_capacity(NULL, cpu);
+
 	/* delta_w is the amount already accumulated against our next period */
 	delta_w = sa->period_contrib;
 	if (delta + delta_w >= 1024) {
--
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