[PATCH 2/3] 3.4.y: time: Avoid making adjustments if we haven't accumulated anything

From: John Stultz
Date: Tue Sep 11 2012 - 15:05:39 EST

This is a -stable backport of bf2ac312195155511a0f79325515cbb61929898a

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

Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
Cc: Prarit Bhargava <prarit@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1345595449-34965-5-git-send-email-john.stultz@xxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Linux Kernel <linux-kernel@xxxxxxxxxxxxxxx>
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
kernel/time/timekeeping.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index dd31d0e..104d549 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1057,9 +1057,12 @@ static void update_wall_time(void)
offset = (clock->read(clock) - clock->cycle_last) & clock->mask;
+ /* Check if there's really nothing to do */
+ if (offset < timekeeper.cycle_interval)
+ goto out;
timekeeper.xtime_nsec = (s64)timekeeper.xtime.tv_nsec <<
* With NO_HZ we may have to accumulate many cycle_intervals
* (think "ticks") worth of time at once. To do this efficiently,

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