[ntp:questions] Re: Regular 16ms jump of NTP on Windows XP SP2
terje.mathisen at hda.hydro.com
Thu Sep 7 13:59:39 UTC 2006
Bert Gøtterup Petersen wrote:
> I didn't think NTP used old timers like that...
This is an OS/Windows HAL layer bug.
> Any idea on how to avoid this?
Replace the OS?
> "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
>> - <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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