[ntp:questions] tickadj -A is broken was -> Re: Loop Frequency and Offset

Doug Calvert dfc-list at douglasfcalvert.net
Mon Sep 26 01:07:00 UTC 2011


tickadj always tells me I am silly when I give it the -A described in
the docs for optimized tick.  I looked at tickadj.c quickly and did
not see any facilities for -A



2011/9/25 Dave Hart <hart at ntp.org>:
> 2011/9/25 Dave Hart <hart at ntp.org>:
>> 2011/9/25 Miguel Gonçalves <mail at miguelgoncalves.com>:
>>
>>> tick# tail -10 /var/log/ntp/loopstats
>>> 55829 66814.311 0.000010871 185.398 0.000003540 0.002317 4
>>> 55829 66831.312 0.000010025 185.398 0.000000984 0.002167 4
>>> 55829 66847.312 0.000011242 185.398 0.000001303 0.002027 4
>>> 55829 66862.313 0.000011571 185.398 0.000000625 0.001896 4
>>> 55829 66877.313 0.000010833 185.398 0.000000990 0.001774 4
>>> 55829 66893.323 0.000011386 185.398 0.000000724 0.001659 4
>>> 55829 66909.314 0.000010876 185.398 0.000000574 0.001552 4
>>> 55829 66927.314 0.000011263 185.398 0.000000620 0.001452 4
>>> 55829 66942.315 0.000011355 185.398 0.000000402 0.001358 4
>>> 55829 66957.315 0.000010197 185.398 0.000001026 0.001270 4
>>>
>> More notable to me:  The frequency compensation is varying.  What
>> version(s) of ntpd are the two machines running?  On the first one,
>> given the loopstats covers less than 300 seconds and the frequency
>> appears locked, I'm guessing you sampled during initial offset
>> convergence.  That's new for 4.2.7 and runs for the first 300 seconds
>> (by default) after the frequency compensation is loaded from driftfile
>> or measured.  During that period, the frequency compensation is locked
>> while ntpd attempts to slew away the initial offset until less than
>> 500 usec remains, or the 300s limit elapses.
>
> Nice theory, Dave, but you overlooked that all those offsets are
> within 500 usec of zero (in fact within +10 to +12 usec), which would
> trigger the end of initial offset convergence and unclamping the
> frequency compensation.
>
> I'd suggest starting with the tickadj correction, and testing again to
> see if the offsets are staying on one side of zero.  I'm still curious
> about the ntpd versions involved.
>
> Cheers,
> Dave Hart
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