[ntp:questions] Re: Regular 16ms jump of NTP on Windows XP SP2

Terje Mathisen terje.mathisen at hda.hydro.com
Thu Sep 7 13:59:39 UTC 2006


Bert Gøtterup Petersen wrote:
> Hi
> 
> I didn't think NTP used old timers like that...

NTP isn't!

This is an OS/Windows HAL layer bug.

> Any idea on how to avoid this?

Replace the OS?
:-)

Terje
> 
> Bert
> 
> "Terje Mathisen" <terje.mathisen at hda.hydro.com> wrote in message 
> news:c4p4t3-ivr.ln1 at osl016lin.hda.hydro.com...
>> Bert Gøtterup Petersen wrote:
>>> When running Windows I see a spike of about 16ms in the loopstats-files 
>>> on all the Windows nodes. The peculiar thing is that the spike occurs 
>>> every 24 hours and 15 minutes per machine, but not at the same time on 
>>> different machines.
>> Hmmm. Could this be an internal windows OS counter wrapping around?
>>
>> 24 hours + 15 min = 86400 + 900 = 87300 s
>>
>> The original keyboard timer chip which generates the Dos 55 ms timer tick 
>> had a 64 K period which was close to but not exactly one hour...
>>
>> 87300 / (24 * 65536) = 0.055038
>>
>> Yes! This is the original DOS timer tick period which Windows is still 
>> emulating for anything running inside a Dos box, as well as programs using 
>> very old Windows APIs.
>>
>> I'm willing to bet that the spike is caused by a once/day fixup of any 
>> residual errors caused by the fact that this emulation isn't totally 
>> accurate!
>>
>> Terje
>> -- 
>> - <Terje.Mathisen at hda.hydro.com>
>> "almost all programming can be viewed as an exercise in caching" 
> 
> 


-- 
- <Terje.Mathisen at hda.hydro.com>
"almost all programming can be viewed as an exercise in caching"




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