[patch V3 20/22] timer: Only wake softirq if necessary

From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Eric Dumazet <edumazet@google.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Chris Mason <clm@fb.com>, Arjan van de Ven <arjan@infradead.org>,
	rt@linutronix.de, Rik van Riel <riel@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	George Spelvin <linux@sciencehorizons.net>,
	Len Brown <lenb@kernel.org>,
	Josh Triplett <josh@joshtriplett.org>
Subject: [patch V3 20/22] timer: Only wake softirq if necessary
Date: Fri, 24 Jun 2016 14:32:20 -0000	[thread overview]
Message-ID: <20160624141723.098625019@linutronix.de> (raw)
In-Reply-To: 20160624140325.554996200@linutronix.de

[-- Attachment #1: timer--Only-wake-softirq-if-necessary.patch --]
[-- Type: text/plain, Size: 802 bytes --]

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>
---
 kernel/time/timer.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1599,7 +1599,18 @@ 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);
 }
 
