[ntp:questions] NTP offset doesn't change.

William Unruh unruh at invalid.ca
Sat Feb 14 01:48:02 UTC 2015


On 2015-02-13, Paul <tik-tok at bodosom.net> wrote:
> On Fri, Feb 13, 2015 at 12:42 AM, William Unruh <unruh at invalid.ca> wrote:
>
>> OK, so we seem to have two different sets of experiments with very
>> different results. Note that I did not erase the drift file, or restart
>> ntpd after my perturbation.
>>
>
> Okay, I offset my clock by 100ms without restarting ntpd.  It took about
> 100 seconds to reduce that by two orders of magnitude and about 2,800
> seconds to return to O(1) microsecond offset albeit O(10) microseconds of
> jitter.   Next I'll try Ntimed-client.  Perhaps you should redo your
> experiment in the modern era.  Or quit referring to stale data.

Good suggestion. I had seen nothing however that caused me to think ntpd
had changed this part.

>
> I had a properly set up PPS source to do the comparison.

As did I.
>
>
> We have no way of knowing that and the simplest way to get poor recovery is
> to use the wrong poll interval with a PPS refclock.
 Poll 4 for PPS, Poll 6-10 for network. I think the test referred to was
 using a local network, but by this time it is hard to remember the
 exact details. Note that since the effective poll interval is 3 higher
 than the nominal poll interval, and since the convergence time scale is
 larger than one poll interval, this would give a convergence time of
 greater than 2^9 sec, or 500 sec (10 min) that is still faster than I
 was finding. 



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