[tip:timers/core] timers: Only wake softirq if necessary

[tip-bot for Thomas Gleixner]

Commit-ID:  4e85876a9d2a977b4a07389da8c07edf76d10825
Gitweb:     http://git.kernel.org/tip/4e85876a9d2a977b4a07389da8c07edf76d10825
Author:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Mon, 4 Jul 2016 09:50:37 +0000
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 7 Jul 2016 10:35:11 +0200

timers: 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@xxxxxxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxx>
Cc: Chris Mason <clm@xxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: George Spelvin <linux@xxxxxxxxxxxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Len Brown <lenb@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: rt@xxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20160704094342.607650550@xxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/time/timer.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 9339d71..8d830f1 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1608,7 +1608,18 @@ static void run_timer_softirq(struct softirq_action *h)
  */
 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);
 }