time: Avoid making adjustments if we haven't accumulated anything

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
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>
Cc: stable@vger.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: Willy Tarreau <w@1wt.eu>

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 85d51c4707e7153c9563f9bd9bcae4cf86c03b28..b451c9376f446166eb0aad87c692132ce4a107eb 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -807,6 +807,10 @@ 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;
 
        /* normally this loop will run just once, however in the