Date: Fri, 16 May 2008 21:30:42 +0200 From: Volker Jahns <volker@thalreit.de> To: Bruce Cran <bruce@cran.org.uk> Cc: freebsd-questions@freebsd.org Subject: Re: time drift Message-ID: <482DE0E2.8020101@thalreit.de> In-Reply-To: <482D549F.9050300@thalreit.de> References: <20080515185758.GA12709@ikarus.thalreit> <597571FB-C72D-4603-B379-A59A435843BE@mac.com> <20080515195302.GA13531@ikarus.thalreit> <20080515203728.GA14284@ikarus.thalreit> <482CA8EE.7040906@cran.org.uk> <482D549F.9050300@thalreit.de>
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Volker Jahns wrote: > Bruce Cran wrote: >> Volker Jahns wrote: >>> On Thu, May 15, 2008 at 09:53:02PM +0200, Volker Jahns wrote: >>>> On Thu, May 15, 2008 at 12:18:57PM -0700, Chuck Swiger wrote: >>>>> On May 15, 2008, at 11:57 AM, Volker Jahns wrote: >>>>>> FreeBSD 6.2 running on X86 hardware (FSC) shows a remarkable >>>>>> time drift >>>>>> >>>>>> running ntpdate every half hour shows that the system looses >>>>>> about 10-14 sec each time. >>>>>> 15 May 10:06:48 ntpdate[7200]: step time server 192.53.103.108 >>>>>> offset -13.799602 sec >>>>>> 15 May 10:36:48 ntpdate[7515]: step time server 192.53.103.108 >>>>>> offset -12.813941 sec >>>>>> 15 May 11:06:48 ntpdate[7879]: step time server 192.53.103.108 >>>>>> offset -13.651921 sec >>>>>> 15 May 11:36:50 ntpdate[8079]: step time server 192.53.103.108 >>>>>> offset -11.109298 sec >>>>>> 15 May 12:06:50 ntpdate[8289]: step time server 192.53.103.108 >>>>>> offset -11.836499 sec >>>>> You should also take a look at the output of "sysctl >>>>> kern.timecounter", and possibly switch to a different mechanism, >>>>> if the existing choice doesn't work out well for your machine... >>>> Thanks for the hint. >>> A few years ago a time drift problem had been observed by a German >>> freebsd >>> user (http://www.freebsd.de/rachive/de-bsd-questions.200304/0643.html). >>> Time drift 15 sec every half hour, ntpd dies away running on his >>> machine. >>> Setting kern.timecounter.hardware to TSC had been recommended as >>> a solution. >> >> There's also a FreeBSD PR open about this problem: >> http://www.freebsd.org/cgi/query-pr.cgi?pr=i386/123462 >> >> > sysctl -w kern.timecounter.hardware=TSC and then this: > 16 May 08:37:01 ntpdate[28819]: adjust time server 192.53.103.108 > offset -0.347027 sec > 16 May 09:07:00 ntpdate[29258]: adjust time server 192.53.103.108 > offset -0.313608 sec > 16 May 09:37:00 ntpdate[29492]: adjust time server 192.53.103.108 > offset -0.314357 sec > 16 May 10:07:00 ntpdate[29826]: adjust time server 192.53.103.108 > offset -0.313694 sec > > > (Please note the use of ntpdate is for debugging purposes only, this > is _not_ an ntp issue) > Finally I want to come back to the time drift issue and howto improve it. Setting kern.timecounter.hardware: i8254 machdep.i8254_freq: 1193182 16 May 12:07:01 ntpdate[31752]: adjust time server 192.53.103.108 offset -0.404453 sec 16 May 12:37:00 ntpdate[32425]: adjust time server 192.53.103.108 offset -0.396156 sec 16 May 13:07:01 ntpdate[32787]: adjust time server 192.53.103.108 offset -0.383712 sec 16 May 13:37:01 ntpdate[33126]: adjust time server 192.53.103.108 offset -0.387233 sec Clock is too slow, frequency must be increased. Corrected machdep.i8254_freq from 1193182 to 1193448 16 May 17:37:00 ntpdate[36310]: adjust time server 192.53.103.108 offset -0.033320 sec 16 May 18:07:01 ntpdate[36632]: adjust time server 192.53.103.108 offset -0.053532 sec 16 May 18:37:00 ntpdate[37011]: adjust time server 192.53.103.108 offset -0.043264 sec 16 May 19:07:01 ntpdate[37361]: adjust time server 192.53.103.108 offset -0.055725 sec Time drift is now only about 50 millisecs per half an hour. -- Volker Jahns, volker@thalreit.de
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