[ntp:questions] ATOM falseticker with flag3 enabled

A C agcarver+ntp at acarver.net
Sat Mar 31 18:12:49 UTC 2012


On 3/30/2012 03:30, David Lord wrote:
> A C wrote:
>> On 3/29/2012 03:29, David Lord wrote:
>>> Dave Hart wrote:
>>>> On Thu, Mar 29, 2012 at 02:44, A C <agcarver+ntp at acarver.net> wrote:
>>>>> Without flag3 it appears that ntpd does the heavy lifting but is
>>>>> unable to
>>>>> use the PPS unless a prefer peer is set. With flag3 enabled, PPS is
>>>>> running
>>>>> without a prefer peer.
>>>>
>>>> Being unable to use the PPS unless either a prefer peer is set or
>>>> another knob is adjusted (see what I quoted earlier) is operating by
>>>> design. The change in operation with flag3 1 seems likely to me to be
>>>> an ntpd bug, which is why I'd like to see a bug report filed. Unless
>>>> I'm missing some design intention, it seems to me PPS should not
>>>> become reachable with no prefer peer regardless of flag3.
>>>
>>>
>>>
>>> On NetBSD-5, i386, I had the PPS marked as falseticker as
>>> from March 2, 2012 when I updated from 4.2.6p3 to 4.2.6p5.
>>> When I went back to 4.2.6p3 the 'o' was back. I hadn't spare
>>> time to investigate and changed config to use only type 20
>>> nmea driver with 4.2.6p5.
>>
>> Interesting, so that's the same OS on two platforms with similar
>> problems. Did you happen to also observe your minimum jitter times in
>> the upgrade? When I run 4.2.6 my minimum jitter is reported as
>> 0.061ms. But in 4.2.7 the minimum jitter is 0.122ms, exactly double
>> the 4.2.6 value.
>>
>> I'm still tinkering with my configuration to see if I can get ATOM to
>> stop being a false ticker but no luck yet even though it's still
>> disciplining the clock.
>
> Jitter depends on time of day, weather etc. The variations
> doesn't seem to have been altered by the update from 4.2.6p3
> to p5.
>
> I didn't tinker as something is obviously broken with
> type 22 driver in p5.

I understand that the jitter will change but I'm talking about the 
minimum possible jitter that ntpd can report for a given system.  Using 
4.2.6, the minimum possible jitter reported (such as what is shown in 
the ntpq billboard when ntpd first starts up) was 0.061 on my NetBSD 
system.  However, with 4.2.7p259 (and some of the earlier versions as 
well) the minimum possible jitter exactly doubled to 0.122 on the same 
system.

It would appear that the method used to compute the minimum possible 
jitter changed between the two versions.


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