linux-kernel - [tip:timers/urgent] tick-sched: Don't call update_wall_time() when delta is lesser than tick

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Date:	Tue, 15 Apr 2014 11:45:44 -0700
From:	tip-bot for Viresh Kumar <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, john.stultz@...aro.org,
	hpa@...or.com, mingo@...nel.org, viresh.kumar@...aro.org,
	tglx@...utronix.de
Subject: [tip:timers/urgent] tick-sched: Don't call update_wall_time()
  when delta is lesser than tick_period

Commit-ID:  03e6bdc5c4d0fc166bfd5d3cf749a5a0c1b5b1bd
Gitweb:     http://git.kernel.org/tip/03e6bdc5c4d0fc166bfd5d3cf749a5a0c1b5b1bd
Author:     Viresh Kumar <viresh.kumar@...aro.org>
AuthorDate: Tue, 15 Apr 2014 10:54:40 +0530
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Tue, 15 Apr 2014 20:26:45 +0200

tick-sched: Don't call update_wall_time() when delta is lesser than tick_period

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>
Cc: <stable@...r.kernel.org> # v3.14+
Link: http://lkml.kernel.org/r/80afb18a494b0bd9710975bcc4de134ae323c74f.1397537987.git.viresh.kumar@linaro.org
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/time/tick-sched.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 9f8af69..e947d96 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -84,6 +84,9 @@ static void tick_do_update_jiffies64(ktime_t now)
 
 		/* 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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