[ntp:questions] NTPD can take 10 hours to achieve stability

Mike S mikes at flatsurface.com
Tue Apr 19 00:16:35 UTC 2011


At 07:43 PM 4/18/2011, Chris Albertson wrote...
>On Mon, Apr 18, 2011 at 4:10 PM, Mike S <mikes at flatsurface.com> wrote:
>. While it certainly doesn't effect most
> > users, it does some. At a minimum, there should be a mechanism to 
> find out
> > what (clock divisors?) the kernel has used for calibration, and 
> lock them in
> > for use with subsequent boots. Maybe there is, but after searching 
> for a
> > while, I couldn't find any way to do that.
>
>Is that not the purpose of the drift file?

Nope. Each time a modern Linux box boots, it tries to calibrate the 
clocksource (to the RTC?). That's necessary because clock source timing 
may change (different processor speed, etc.). That calibration isn't 
perfect, and the "calibrated" clocksource can vary by 40 or more ppm 
from boot to boot. Then, your drift file is off by 40 or more ppm, and 
NTP has to reconverge on the proper value for the new clocksource 
calibration.

That's the problem - it makes the drift file practically useless.




More information about the questions mailing list