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

Harlan Stenn stenn at ntp.org
Mon Apr 18 19:51:23 UTC 2011


David wrote:
> Bill wrote:
> > IF your file has the correct drift information in it (linux for example
> > with the tsc clock changes its drift about 40PPM on each bootup) and if
> > it has not been very long since the machine was switched off, then yes,
> > it will be accurate very fast. Those are big ifs. The question is how
> > long does it take ntpd to recover from errors. The figures I gave above
> > give you a clue. chrony is at least an order of magnitude faster.
> 
> Well, if Linux is that badly behaved (altering its clock on each
> boot), I would have said that was an OS defect which needed
> correction, not altering ntpd to accommodate faulty software!

I think, and I am really not sure, that the linux kernel calibrates its
clock on each boot, and that calibration can be different in the
low-order bit (or few) each time.

This means that any value stored in the drift file may be for a slightly
different frequency.

I would like to see a better solution for this problem other than "live
with it or always throw the drift value away on startup".

H



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