[tip:timers/urgent] time: Avoid making adjustments if we haven't accumulated anything

[tip-bot for John Stultz]

Commit-ID:  bf2ac312195155511a0f79325515cbb61929898a
Gitweb:     http://git.kernel.org/tip/bf2ac312195155511a0f79325515cbb61929898a
Author:     John Stultz <john.stultz@xxxxxxxxxx>
AuthorDate: Tue, 21 Aug 2012 20:30:49 -0400
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
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@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>
---
 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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