sched/cpufreq: Optimize cpufreq update kicker to avoid update multiple times

Sometimes delta_exec is 0 due to update_curr() is called multiple times,
this is captured by:

	u64 delta_exec = rq_clock_task(rq) - curr->se.exec_start;

This patch optimizes the cpufreq update kicker by bailing out when nothing
changed, it will benefit the upcoming schedutil, since otherwise it will
(over)react to the special util/max combination.

Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1461316044-9520-1-git-send-email-wanpeng.li@hotmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index c41ea7ac1764..19e13060fcd5 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -953,14 +953,14 @@ static void update_curr_rt(struct rq *rq)
         if (curr->sched_class != &rt_sched_class)
                 return;
 
-        /* Kick cpufreq (see the comment in linux/cpufreq.h). */
-        if (cpu_of(rq) == smp_processor_id())
-                cpufreq_trigger_update(rq_clock(rq));
-
         delta_exec = rq_clock_task(rq) - curr->se.exec_start;
         if (unlikely((s64)delta_exec <= 0))
                 return;
 
+        /* Kick cpufreq (see the comment in linux/cpufreq.h). */
+        if (cpu_of(rq) == smp_processor_id())
+                cpufreq_trigger_update(rq_clock(rq));
+
         schedstat_set(curr->se.statistics.exec_max,
                       max(curr->se.statistics.exec_max, delta_exec));