47 lines
1.8 KiB
Diff
47 lines
1.8 KiB
Diff
commit 99c392d8ba163e35b9d562dd4bcf7dd476ad3573
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Author: Karel Zak <kzak@redhat.com>
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Date: Tue Mar 20 00:32:37 2007 +0100
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hwclock: fix --systohc sets clock 0.5 seconds slow
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quote from rh150493:
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The kernel code, when setting the BIOS clock notes that the clock time
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ticks to the next second 0.5 seconds after adjusting it (see
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linux/arch/i386/kernel/time.c).
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hwclock --systohc sets the CMOS clock at the 1 second boundry and thus
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causes the clock to be wrong by 500ms each time it is reset. If the
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clock is set every shutdown then the clock will have a reboot-count
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related drift as well as the natural drift problems of the clock. Note
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that this also mucks up the drift calculations, of course.
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Signed-off-by: Karel Zak <kzak@redhat.com>
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diff --git a/hwclock/hwclock.c b/hwclock/hwclock.c
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index 9731dad..820c388 100644
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--- a/hwclock/hwclock.c
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+++ b/hwclock/hwclock.c
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@@ -517,14 +517,19 @@ set_hardware_clock_exact(const time_t sethwtime,
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"Delaying further to reach the next full second.\n"),
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time_diff(beginsystime, refsystime));
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- /* Now delay some more until Hardware Clock time newhwtime arrives */
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+ /*
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+ * Now delay some more until Hardware Clock time newhwtime arrives. The -500
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+ * ms is because the Hardware Clock always sets to your set time plus 500 ms
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+ * (because it is designed to update to the next second precisely 500 ms
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+ * after you finish the setting).
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+ */
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do {
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float tdiff;
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gettimeofday(&nowsystime, NULL);
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tdiff = time_diff(nowsystime, beginsystime);
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if (tdiff < 0)
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goto time_resync; /* probably time was reset */
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- } while (time_diff(nowsystime, refsystime) < newhwtime - sethwtime);
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+ } while (time_diff(nowsystime, refsystime) - 0.5 < newhwtime - sethwtime);
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set_hardware_clock(newhwtime, universal, testing);
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}
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