[ntp:questions] Clock skew changes drastically between reboots

Spoon devnull at localhost.com
Mon Apr 2 14:31:32 UTC 2007


Hans Jørgen Jakobsen wrote:

> Dmitry Ivanov wrote:
> 
>> Spoon wrote:
>> 
>>> I've noticed something I find very strange on the systems I have to
>>> work with. Every time I reboot the computer, the clock skew of the local
>>> clock changes, sometimes by what seems to be a huge amount.
>>>
>>> For example, I boot the computer, let ntpd run for 12 hours, and the
>>> value recorded in the drift file is 35 ppm. I reboot the computer, let
>>> ntpd run for 12 hours, and I get 5 ppm...
>> 
>> I see the same behaviour on many systems. Looks like common problem.
> 
> Could it be that some systems at reboot try to calibrate the clock
> (whatever that might be) relative to the TOD chip?
> On some systems the TOD chip has the lowest frequency offset
> and this would on systems not runing NTP lead to a system drifting less.
> But it's poison for the value in the driftfile.

# dmesg | grep -i calib
Calibrating delay using timer specific routine..
   2535.15 BogoMIPS (lpj=12675781)

Are you referring to this calibration?

(I run Linux 2.6.20.3-rt8)

I'll check the source code to find where this message comes from.

Regards.




More information about the questions mailing list