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