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[2/3] 3.2.y: time: Avoid making adjustments if we haven't accumulated anything

Message ID 1347402926-34813-3-git-send-email-john.stultz@linaro.org
State Accepted
Headers show

Commit Message

John Stultz Sept. 11, 2012, 10:35 p.m. UTC 
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>
---
 kernel/time/timekeeping.c |    4 ++++
 1 file changed, 4 insertions(+)
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Patch

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 36440c88..59544dc 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1033,6 +1033,10 @@  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)
+		return;
+
 	timekeeper.xtime_nsec = (s64)xtime.tv_nsec << timekeeper.shift;
 
 	/*