[ntp:questions] clockstats pausing during ntpq poll

A C agcarver+ntp at acarver.net
Fri Feb 17 22:11:00 UTC 2012


On 2/17/2012 13:47, unruh wrote:
> On 2012-02-17, A C<agcarver+ntp at acarver.net>  wrote:
>> On 2/17/2012 09:23, Dave Hart wrote:
>>> On Fri, Feb 17, 2012 at 16:44, unruh<unruh at invalid.ca>   wrote:
>>>> On 2012-02-17, Dave Hart<hart at ntp.org>   wrote:
>>>>> On Fri, Feb 17, 2012 at 06:06, A C<agcarver+ntp at acarver.net>   wrote:
>>
>>>>>> What I've noticed is that normally the clockstats is updated once per second
>>>>>> as the PPS ticks. ?However, during a query by the remote ntpq instance, the
>>>>>> clockstats file pauses for about one second and then resumes. ?You can see
>>>>>> it below in a direct copy from the clockstats file. ?There's a missing
>>>>>> 'tick' at 21828 seconds and one at 21832. ?PPS is most certainly ticking at
>>>>>> these times. ?It is extremely obvious, when the two terminal windows are
>>>>>> side by side, that the ntpq poll freezes ntpd.
>>
>>>>> Round those figures in the 2nd column to whole seconds and you'll note
>>>>> there are no missing PPS events.  You don't say which ntpq query, so
>>>>
>>>> Uh. Yes, there are!. Maybe no the ones he mentions, but there are
>>>> missing seconds.
>>>>
>>>> The rounded figures are
>>>> 23 24 26 27 28 29 31 32 33
>>>>       ^           ^
>>>
>>> Good catch, I obviously need to get more sleep.
>
>> I restarted ntpd and everything seems to be fine now.  This had worked
>> very well up until last night when I was getting the missing seconds.
>> After restarting ntpd, the condition went away.  I'm watching ntpq poll
>> ntpd regularly and the clockstats file is not missing an update anymore
>>
>> I'll keep watching it as it runs to see if it comes back.  Now to follow
>> the PPM vs. flag3 trail plus finish compiling the fixes to libc (the
>> libc error has been found).
>
> It could also be that your gps card is missing some seconds. Eg, if the
> sattelites are suddenly all no visible to the card, it will not send a
> pulse.
>
> I occasionally get missing seconds from my Sure gps. I sometimes get
> missing hours. Not sure why, except that the antenna only sees about 1/4
> of the full sky. But it is hard to imagine that no sattelites pass
> through that region for an hour.

I had thought of that but at the time of the issue there were nine 
satellites in view with signal levels greater than 35 db-Hz (I collect 
the GPS data for another experiment).  I have about a 5/6 view of the 
sky (two mountain ranges block the low sky on two sides).

Either way it seems to be ok now.  Now I'm just trying to figure out how 
the PPM stepping works with the two flag3 settings (see other thread).


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