sched/fair: Do not call cpufreq hook unless util changed

There's no reason to call the cpufreq hook if the root cfs_rq
utilization has not been modified.

Signed-off-by: Steve Muckle <smuckle@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Juri Lelli <Juri.Lelli@arm.com>
Cc: Michael Turquette <mturquette@baylibre.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Link: http://lkml.kernel.org/r/1458606068-7476-2-git-send-email-smuckle@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/fair.c

@@ -2879,20 +2879,21 @@ static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
 {
 	struct sched_avg *sa = &cfs_rq->avg;
 	struct rq *rq = rq_of(cfs_rq);
-	int decayed, removed = 0;
+	int decayed, removed_load = 0, removed_util = 0;
 	int cpu = cpu_of(rq);
 
 	if (atomic_long_read(&cfs_rq->removed_load_avg)) {
 		s64 r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
 		sa->load_avg = max_t(long, sa->load_avg - r, 0);
 		sa->load_sum = max_t(s64, sa->load_sum - r * LOAD_AVG_MAX, 0);
-		removed = 1;
+		removed_load = 1;
 	}
 
 	if (atomic_long_read(&cfs_rq->removed_util_avg)) {
 		long r = atomic_long_xchg(&cfs_rq->removed_util_avg, 0);
 		sa->util_avg = max_t(long, sa->util_avg - r, 0);
 		sa->util_sum = max_t(s32, sa->util_sum - r * LOAD_AVG_MAX, 0);
+		removed_util = 1;
 	}
 
 	decayed = __update_load_avg(now, cpu, sa,
@@ -2903,7 +2904,8 @@ static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
 	cfs_rq->load_last_update_time_copy = sa->last_update_time;
 #endif
 
-	if (cpu == smp_processor_id() && &rq->cfs == cfs_rq) {
+	if (cpu == smp_processor_id() && &rq->cfs == cfs_rq &&
+	    (decayed || removed_util)) {
 		unsigned long max = rq->cpu_capacity_orig;
 
 		/*
@@ -2926,7 +2928,7 @@ static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
 				    min(sa->util_avg, max), max);
 	}
 
-	return decayed || removed;
+	return decayed || removed_load;
 }
 
 /* Update task and its cfs_rq load average */