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@linutronix.de>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Chris Mason <clm@fb.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: George Spelvin <linux@sciencehorizons.net>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Len Brown <lenb@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20160704094342.607650550@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 9339d71ee998..8d830f1f6a6a 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);
 }