From: Thomas Gleixner <tglx@linutronix.de>
Date: Mon, 4 Jul 2016 09:50:37 +0000
Subject: [PATCH 20/22] timer: Only wake softirq if necessary

With the wheel forwading in place and with the HZ=1000 4ms folding we can
avoid running the softirq at all.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/time/timer.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1623,7 +1623,18 @@ static void run_timer_softirq(struct sof
  */
 void run_local_timers(void)
 {
+	struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
+
 	hrtimer_run_queues();
+	/* Raise the softirq only if required. */
+	if (time_before(jiffies, base->clk)) {
+		if (!IS_ENABLED(CONFIG_NO_HZ_COMMON) || !base->nohz_active)
+			return;
+		/* CPU is awake, so check the deferrable base. */
+		base++;
+		if (time_before(jiffies, base->clk))
+			return;
+	}
 	raise_softirq(TIMER_SOFTIRQ);
 }
 
