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

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>
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>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index fd06ae8555613f0bff0ad53a3993d3f5d4a23800..df9447b35026e4fcfd54e63e27a13bf9770fd143 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1055,6 +1055,10 @@ static void update_wall_time(void)
 #else
        offset = (clock->read(clock) - clock->cycle_last) & clock->mask;
 #endif
+       /* Check if there's really nothing to do */
+       if (offset < timekeeper.cycle_interval)
+               goto out;
+
        timekeeper.xtime_nsec = (s64)timekeeper.xtime.tv_nsec <<
                                                timekeeper.shift;