[ntp:questions] Re: Windows timekeeping - sudden degradation - why?

Danny Mayer mayer at ntp.isc.org
Fri Dec 16 02:31:19 UTC 2005

John Allen wrote:
> John Allen wrote:
>> Richard B. Gilbert wrote:
>>  >My guess would be that your local clock has a frequency error well in
>>  >excess of 500 parts per million!   If that is the case, you will
>>  >probably have to replace the mother board to fix it.
>> As you say, the hopeless inaccuracy of the system clock might be cured
>> only by a new motherboard, although it seems strange that for more
>> than a year it seemed to work fairly well.
> I really was going to give up on this when I made what could be a useful
> discovery. While reading of recurrent problems with system clocks on
> nForce2 motherboards, eg these threads:
> http://www.nforcershq.com/forum/1-vt19631.html
> http://kerneltrap.org/node/4872
> I found references to possibly using a different HAL (Hardware
> Abstraction Layer). I then did what was probably not wise, which was to
> change from
> "ACPI Uniprocessor PC" to "Advanced Configuration and Power Interface
> (ACPI) PC". I also set the BIOS option "FSB Spread Spectrum" to "disabled".
> By good fortune this did not stop the PC working but it has had the
> result that the system clock has been very stable for 24 hours and NTP
> is now working properly, with offsets of no more than 7 ms (from the NTP
> server on my LAN) over long periods:
>>ntpq -c "rv 0"
> assID=0 status=4644 leap_add_sec, sync_ntp, 4 events, event_peer/strat_chg,
> version="ntpd  2004 May 07 8:37:39  (1)"?, processor="unknown",
> system="WINDOWS/NT", leap=01, stratum=4, precision=-20,
> rootdelay=58.614, rootdispersion=153.312, peer=7996, refid=,
> reftime=c74ae7bc.223db21c  Wed, Dec 14 2005 19:49:32.133, poll=9,
> clock=0xc74ae8e7.5bfd448c, state=4, offset=-7.045, frequency=-7.005,
> noise=3.010, jitter=0.955, stability=1.529
> It may be that this HAL change only works because it disables the APIC
> (Advanced Programmable Interrupt Controller); at any rate, it has made
> me realise how far one can go from what initially appeared to be an NTP
> issue.
> I've noticed that some other threads in this newsgroup have concerned
> PCs with nForce2 motherboards, so this could be a useful hint. However,
> changing HALs should not be done without careful reflection and a
> willingness to reinstall Windows if something goes wrong.
> This site (in German) gives some more information:
> http://www.planet3dnow.de/artikel/diverses/nf2config/3.shtml#config_apic
> as does this:
> http://support.microsoft.com/?kbid=821893
> Moral of the story: if NTP seems to stop working properly and you have
> an nForce2 motherboard (a) the problem is quite possibly not NTP and (b)
> you may not need a new motherboard...

Can you add this to the our Support Twiki? It's always useful to have
this kind of thing easily available and not to have to stumble across it.


> John
> -- 
> John Allen
> Bofferdange, Luxembourg
> allen{at}vo{dot}lu
> http://www.homepages.lu/allen

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