[ntp:questions] Re: ntpd PLL and clock overshoot
David L. Mills
mills at udel.edu
Mon Oct 16 20:15:29 UTC 2006
I have made the point on past occasions that NTP may be more valuable as
a hardware/software canary than as a clock winder.
Please forgive the broken "from" line in some of my messages.
Apparently, the problem is not in the news server here, but may be in
Netscape 7.2, which I have been using for some time and didn't use to do
that offense. Workin' on it.
Uwe Klein wrote:
> David L. Mills wrote:
>> With all of the machines here, including FreeBSD, Solaris, HP-UX,
>> SunOS, Tru64 and HP-UX, the loop response in steady state is as I
>> reported earlier. The results with Linux are highly suspect, as at
>> least in some cases the timer interrupt frequency has been changed
>> significantly without compensation in the kernel parameters. I have
>> recommended to avoid Linux in any case involving precision timekeeping.
> Hello Dave,
> there is at least one issue with APIC routed interupts on linux running
> on nVidia nForce 1 and 2 based Boards resulting in a too fast and
> irregular clock.
> It seems the timer interrupt is handled _twice_ on occasion.
> I have A7N266-E and A7N8X-E boards produce this problem with various
> in the 2.6.1n range.
> The same boards ran ntpd on linux 2.4 and no APIC routing just perfect.
> The clock starts to run ahead by ~8-900ppm resulting in hard correction
> of -.5 to -1.5 seconds every couple of hours. Adjusting the system tick
> results in symetric corrections +.5 .. -.5 which would indicate an
> unstable clock.
> This started out for me as a problem with ntpd not syncing
> BUT is now Linux/Hardware related with ntpd being the whistle-blower.
> One of the reasons i started reading this group some weeks ago.
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