[v2.6.34-stable 03/77] time: Avoid making adjustments if we haven't accumulated anything

Paul Gortmaker
2013-01-08T23:51:14Z

From: John Stultz <john.stultz@linaro.org>

-------------------
This is a commit scheduled for the next v2.6.34 longterm release.
http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
If you see a problem with using this for longterm, please comment.
-------------------

commit bf2ac312195155511a0f79325515cbb61929898a upstream.

If update_wall_time() is called and the current offset isn't large
enough to accumulate, avoid re-calling timekeeping_adjust which may
change the clock freq and can cause 1ns inconsistencies with
CLOCK_REALTIME_COARSE/CLOCK_MONOTONIC_COARSE.

Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Link: http://lkml.kernel.org/r/1345595449-34965-5-git-send-email-john.stultz@linaro.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
kernel/time/timekeeping.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 0d59077..bbdad71 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -849,6 +849,10 @@ void update_wall_time(void)
#else
offset = timekeeper.cycle_interval;
#endif
+ /* Check if there's really nothing to do */
+ if (offset < timekeeper.cycle_interval)
+ return;
+
timekeeper.xtime_nsec = (s64)xtime.tv_nsec << timekeeper.shift;

/*
--
1.7.12.1