From: Ingo Molnar <mingo@elte.hu>
Date: Mon, 12 May 2008 13:43:53 +0000 (+0200)
Subject: nohz: reduce jiffies polling overhead
X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=7a14ce1d8c1d3a6118d406e64eaf9aa70375e085;p=deliverable%2Flinux.git

nohz: reduce jiffies polling overhead

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index b854a895591e..cb75394ed00e 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -48,6 +48,13 @@ static void tick_do_update_jiffies64(ktime_t now)
 	unsigned long ticks = 0;
 	ktime_t delta;
 
+	/*
+	 * Do a quick check without holding xtime_lock:
+	 */
+	delta = ktime_sub(now, last_jiffies_update);
+	if (delta.tv64 < tick_period.tv64)
+		return;
+
 	/* Reevalute with xtime_lock held */
 	write_seqlock(&xtime_lock);