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Date:      Wed, 01 May 2002 13:49:08 +0200
From:      Daniel Rock <D.Rock@t-online.de>
To:        current@freebsd.org
Subject:   clock drift in -CURRENT
Message-ID:  <3CCFD634.6F7D20B1@t-online.de>

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Hi,

after almost 50 days of uptime I suddenly noticed an extreme clock drift
in current. Here is an excerpt from my /var/log/messages (March 8th was my
last reboot time):

Mar  8 18:38:07 gate syslogd: kernel boot file is /boot/kernel/kernel
Mar  8 18:38:07 gate kernel: Copyright (c) 1992-2002 The FreeBSD Project.
[...]
Apr 27 20:03:10 gate ntpd[157]: time reset -0.250532 s
Apr 27 20:18:14 gate ntpd[157]: time reset 0.446208 s
Apr 27 20:39:57 gate ntpd[157]: time reset -0.820100 s
Apr 27 21:11:19 gate ntpd[157]: time reset 0.887949 s
Apr 27 21:25:33 gate ntpd[157]: time reset -0.228488 s
Apr 27 21:54:35 gate ntpd[157]: time reset -0.395676 s
Apr 28 12:59:15 gate ntpd[157]: time reset -0.381327 s
Apr 28 13:19:52 gate ntpd[157]: time reset 0.815323 s
Apr 28 13:31:50 gate ntpd[157]: time reset 0.844171 s
Apr 28 13:58:52 gate ntpd[157]: time reset 1.447538 s
Apr 28 14:14:58 gate ntpd[157]: time reset 0.915263 s
Apr 28 14:36:38 gate ntpd[157]: time reset 0.860966 s
Apr 28 14:47:29 gate ntpd[157]: time reset 0.984839 s
Apr 28 15:06:59 gate ntpd[157]: time reset 1.025584 s
Apr 28 15:27:32 gate ntpd[157]: time reset 1.156623 s
Apr 28 15:48:59 gate ntpd[157]: time reset 0.896726 s
Apr 28 16:00:52 gate ntpd[157]: time reset 0.973291 s
Apr 28 16:24:24 gate ntpd[157]: time reset 1.212415 s
Apr 28 16:37:19 gate ntpd[157]: time reset 0.859379 s
Apr 28 16:56:49 gate ntpd[157]: time reset 0.914863 s
Apr 28 17:13:05 gate ntpd[157]: time reset 1.100234 s
Apr 28 17:35:59 gate ntpd[157]: time reset 1.231416 s
Apr 28 17:59:53 gate ntpd[157]: time reset 1.026558 s
Apr 28 18:11:59 gate ntpd[157]: time reset 0.995554 s
Apr 28 18:34:45 gate ntpd[157]: time reset 1.140261 s
Apr 28 18:54:19 gate ntpd[157]: time reset 0.856611 s
Apr 28 19:07:15 gate ntpd[157]: time reset 1.094226 s
Apr 28 19:22:30 gate ntpd[157]: time reset 0.879816 s
Apr 28 19:47:25 gate ntpd[157]: time reset 1.332108 s
Apr 28 20:06:56 gate ntpd[157]: time reset 0.949128 s
Apr 28 20:28:27 gate ntpd[157]: time reset 0.906657 s
Apr 28 20:41:37 gate ntpd[157]: time reset 0.877976 s
Apr 28 20:57:57 gate ntpd[157]: time reset 1.103012 s
Apr 28 21:28:19 gate ntpd[157]: time reset 1.607870 s
Apr 28 21:59:43 gate ntpd[157]: time reset 1.253603 s
Apr 28 22:14:46 gate ntpd[157]: time reset 1.181729 s
Apr 28 22:47:13 gate ntpd[157]: time reset 1.573263 s
Apr 28 23:07:47 gate ntpd[157]: time reset 0.836291 s
Apr 28 23:20:52 gate ntpd[157]: time reset 1.105955 s
Apr 28 23:35:59 gate ntpd[157]: time reset 0.839469 s
[...]

So the machine is losing a second every 20 minutes. After a reboot everything
was OK again.

The drift began exactly at the moment the counter for clock interrupts got
past the 2^31 mark (I have HZ=500 in the kernel):
500 ticks/s * 49.7 days ~ 2^31 ticks

After a reboot everything went ok again.

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