linux-kernel - [PATCH 3.14 018/140] tick-sched: Dont call update_wall_time() when delta is lesser than tick

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Date:	Wed, 28 May 2014 21:32:37 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Viresh Kumar <viresh.kumar@...aro.org>,
	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linaro-kernel@...ts.linaro.org, fweisbec@...il.com,
	Arvind.Chauhan@....com, linaro-networking@...aro.org
Subject: [PATCH 3.14 018/140] tick-sched: Dont call update_wall_time() when delta is lesser than tick_period

3.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Viresh Kumar <viresh.kumar@...aro.org>

commit 03e6bdc5c4d0fc166bfd5d3cf749a5a0c1b5b1bd upstream.

In tick_do_update_jiffies64() we are processing ticks only if delta is
greater than tick_period. This is what we are supposed to do here and
it broke a bit with this patch:

commit 47a1b796 (tick/timekeeping: Call update_wall_time outside the
jiffies lock)

With above patch, we might end up calling update_wall_time() even if
delta is found to be smaller that tick_period. Fix this by returning
when the delta is less than tick period.

[ tglx: Made it a 3 liner and massaged changelog ]

Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
Cc: linaro-kernel@...ts.linaro.org
Cc: fweisbec@...il.com
Cc: Arvind.Chauhan@....com
Cc: linaro-networking@...aro.org
Cc: John Stultz <john.stultz@...aro.org>
Link: http://lkml.kernel.org/r/80afb18a494b0bd9710975bcc4de134ae323c74f.1397537987.git.viresh.kumar@linaro.org
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/time/tick-sched.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -84,6 +84,9 @@ static void tick_do_update_jiffies64(kti
 
 		/* Keep the tick_next_period variable up to date */
 		tick_next_period = ktime_add(last_jiffies_update, tick_period);
+	} else {
+		write_sequnlock(&jiffies_lock);
+		return;
 	}
 	write_sequnlock(&jiffies_lock);
 	update_wall_time();


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