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

Tom Smith smith at cag.zko.hp.com
Sun Dec 4 12:46:41 UTC 2005

The high jitter numbers may just be because of that system's
own instability.

Have you checked the current drift rate? That might have gotten
disrupted, especially if there was network activity involved in your
experiment. Try the ntpq command "rv 0" or "ntpdc -c loopinfo" and look
for the frequency. It should have an absolute value of under 100. If it's
several hundred, you may need to re-initialize NTP by stopping it,
deleting the drift file, and then restarting it. In any case,
sample it periodically and see if it is oscillating.

Any network related changes at that time, for example, on a switch? If it's
fast ethernet, maybe you've renegotiated or otherwise acquired a mismatched
speed/mode and you're now suffering packet losses. You might want to look at
"netstat -e -s" and see if you have a significant number of errors or see if
the "reach" output from "ntpq -p" looks different on this system than on others.


David J Taylor wrote:
> Folks,
> I run a number of NTP systems based on Windows, and normally all but the 
> Windows 2000 Workstation keep good time.  In particular, the Windows XP 
> SP2 system kept good time until about 14:00 UTC on Friday 2nd December.
>   http://www.david-taylor.myby.co.uk/mrtg/odin_ntp.html
> I asked myself what changed on the system and, as far as I know, the 
> answer is nothing!  Around that time, I was developing a program for 
> processing large images, and fed it an image which was too large.  Perhaps 
> coincidental - perhaps not.  The pagefile size is fixed at 2GB and seems 
> to still be the same.  I wondered if disk I/O had become switched from 
> UDMA to PIO, but its seems not.  I've checked for spyware and neither 
> SpyBot nor AdAware find anything other than cookies.  I don't see anything 
> unusual in Services.  I even did a system restore to around 12:58 (IIRC) 
> on the day in question, but this didn't cure the problem.
> I'm stuck!  Can you help?  Why would an otherwise good timekeeper become 
> degraded in this way?  The jitter figures (from ntpq -p) are in the 10 - 
> 15 millisecond range, even for servers on the LAN, whereas other PCs on 
> the same LAN show jitter under a millisecond.  Lan traffic looks normal, 
> though.  The delay figures look normal as well.
> Any ideas?  (no, replacing XP is not an option!).
> Thanks,
> David 

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