[ntp:questions] Speed of ntp convergence
Martin Burnicki
martin.burnicki at meinberg.de
Thu Nov 6 09:50:48 UTC 2008
David J Taylor wrote:
> Unruh wrote:
> []
>> An hour later, it was still 7ms off, another hour, 2.6ms and another
>> hour
>> later, still 1.2 ms off. Ie, only after about 6 hours was it within a
>> ms of
>> the correct time. Now, usually this PPS controls the time to within
>> about 2us (not ms, usec) but it is apparently going to take over 10
>> hours to get
>> there. That is of course completely rediculous.
>
> There sounds to be something wrong with your system.
As mentioned in another reply, AFAIR older versions of the NTP daemon did
converge quite a bit faster than recent versions.
> As a comparison, I have a very old Pentium 133 system here running FreeBSD
> with local GPS PPS and some other Internet-based stratum 2/3 servers
> (probably NTP pool and a fixed name). I'm sure it's well within a few
> minutes for it to reach it's full accuracy (tens of microseconds). For
> interest, I've just (0645 UTC) switched it off and on, and we will be able
> to watch its recovery here (30 minute updates):
>
> http://www.satsignal.eu/mrtg/pixie_ntp.html
>
> Here it is about a minute after startup:
>
> ntpq -p pixie
> remote refid st t when poll reach delay offset
> jitter
>
==============================================================================
> +calx.pulsewidth 193.120.10.3 2 u 62 64 1 22.272 1.700
> 0.743
> +admin.islay.bit 192.33.96.102 2 u 62 64 1 21.131 0.921
> 1.112
> +dnscache-london 128.250.33.242 2 u 62 64 1 22.845 3.299
> 0.666
> 88-96-233-89.ds .PPS. 1 u 14 128 7 63.431 0.044
> 2.789
> *utserv.mcc.ac.u 193.62.22.98 2 u 64 64 1 26.494 4.312
> 0.829
> GPS_NMEA(1) .PPS. 0 l 12 64 3 0.000 -0.137
> 1.654
>
> .. and a few minutes later ...
>
> ntpq -p pixie
> remote refid st t when poll reach delay offset
> jitter
>
==============================================================================
> +calx.pulsewidth 193.120.10.3 2 u 54 64 37 22.348 2.946
> 0.877
> +admin.islay.bit 192.33.96.102 2 u 53 64 37 20.496 1.862
> 1.057
> +dnscache-london 128.250.33.242 2 u 57 64 37 23.090 3.809
> 0.662
> 88-96-233-89.ds .PPS. 1 u 134 256 17 63.431 0.044
> 2.007
> +utserv.mcc.ac.u 193.62.22.98 2 u 53 64 37 25.564 5.371
> 0.868
> *GPS_NMEA(1) .PPS. 0 l 3 64 77 0.000 -0.001
> 0.803
>
> It's using the out-of-the-box NTP code, and probably a rather old version
> of NTP.
>
> version="ntpd 4.2.0-a Sun May 8 06:01:21 UTC 2005 (1)"
Now the question is how a recent version of ntpd would converge on this
machine.
Martin
--
Martin Burnicki
Meinberg Funkuhren
Bad Pyrmont
Germany
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