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Subject[tip:timers/urgent] time: Avoid making adjustments if we haven' t accumulated anything
Commit-ID:  bf2ac312195155511a0f79325515cbb61929898a
Gitweb: http://git.kernel.org/tip/bf2ac312195155511a0f79325515cbb61929898a
Author: John Stultz <john.stultz@linaro.org>
AuthorDate: Tue, 21 Aug 2012 20:30:49 -0400
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Wed, 22 Aug 2012 10:42:13 +0200

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

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>
---
kernel/time/timekeeping.c | 4 ++++
1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index a5a9389..0c1485e 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1152,6 +1152,10 @@ static void update_wall_time(void)
offset = (clock->read(clock) - clock->cycle_last) & clock->mask;
#endif

+ /* Check if there's really nothing to do */
+ if (offset < tk->cycle_interval)
+ goto out;
+
/*
* 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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