[ntp:questions] what happens with overload on system for NTP
david at ex.djwhome.demon.invalid
Tue Feb 9 22:04:14 UTC 2010
Ananth Shenoy wrote:
> NTP version 4.2.0
> I'am currently working on a problem on NTP. NTP log files show lot of
> drift.. The offset and frequency keep increasing and once the frequency
> rises above 500ppm the NTP displays error message.
> frequency error 513 PPM exceeds tolerance 500 PPM
> we see the offset bouncing around in +ve and -ve values sometimes high and low.
> what could be the cause of this ?
What OS. Please confirm that you are running this on a physical machine
as one thing that could easily cause this is trying to run nptd on a
On a real machine, this would indicate a grossly overloaded network, or
a device driver with poor latency. Goint to the frequency end stop in
one direction can also mean a very bad motherboard crystal.
Power management can also cause problems, and should be disabled.
> Also, what are the effects of heavy load on the system ?
> If suppose NTP is running on low priority and some high priority
You would have a broken ntp installation. On systems that support it,
ntpd tries to set real time priority.
> processes continously preempt NTP from getting the CPU what will happen.
> Will then calculations of offset go wrong ?
The calculation will not go wrong, but the scheduling delays will come a
significant part of the error term. Note that, when working properly,
offset is all error term.
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