Fix RTC updates from ntp (rhbz 985522)

1 files changed, 44 insertions, 0 deletions

diff --git a/ntp-Make-periodic-RTC-update-more-reliable.patch b/ntp-Make-periodic-RTC-update-more-reliable.patch
new file mode 100644
index 000000000..59179e719
--- /dev/null
+++ b/ntp-Make-periodic-RTC-update-more-reliable.patch
@@ -0,0 +1,44 @@
+From a97ad0c4b447a132a322cedc3a5f7fa4cab4b304 Mon Sep 17 00:00:00 2001
+From: Miroslav Lichvar <mlichvar@redhat.com>
+Date: Thu, 1 Aug 2013 19:31:35 +0200
+Subject: [PATCH] ntp: Make periodic RTC update more reliable
+
+The current code requires that the scheduled update of the RTC happens
+in the closest tick to the half of the second. This seems to be
+difficult to achieve reliably. The scheduled work may be missing the
+target time by a tick or two and be constantly rescheduled every second.
+
+Relax the limit to 10 ticks. As a typical RTC drifts in the 11-minute
+update interval by several milliseconds, this shouldn't affect the
+overall accuracy of the RTC much.
+
+Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
+Signed-off-by: John Stultz <john.stultz@linaro.org>
+---
+ kernel/time/ntp.c |    3 ++-
+ 1 file changed, 2 insertions(+), 1 deletion(-)
+
+diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
+index 8f5b3b9..ab1fa7c 100644
+--- a/kernel/time/ntp.c
++++ b/kernel/time/ntp.c
+@@ -475,6 +475,7 @@ static void sync_cmos_clock(struct work_struct *work)
+ 	 * called as close as possible to 500 ms before the new second starts.
+ 	 * This code is run on a timer.  If the clock is set, that timer
+ 	 * may not expire at the correct time.  Thus, we adjust...
++	 * We want the clock to be within a couple of ticks from the target.
+ 	 */
+ 	if (!ntp_synced()) {
+ 		/*
+@@ -485,7 +486,7 @@ static void sync_cmos_clock(struct work_struct *work)
+ 	}
+ 
+ 	getnstimeofday(&now);
+-	if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2) {
++	if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec * 5) {
+ 		struct timespec adjust = now;
+ 
+ 		fail = -ENODEV;
+-- 
+1.7.9.5
+