[ntp:questions] ntp-dev-4.2.7p253 root dispersion 1ms limit

Kasper Pedersen ntp at taur.dk
Sat Jan 28 22:02:46 UTC 2012


Can anyone give me a hint to understanding this difference between root
dispersion, as reported by the production version, and the dev version,
of ntpd?

My test machine has a very stable oscillator, and a good PPS source.
configuration is below:  a PPS source, gpsd though SHM, and a local server.

When running the production (4.2.6p5) ntpd, I see root dispersion settle
to a handful of microseconds. It increments at the dispersion (15us/s),
as documented, until pulled back down on the next update.

When running the DEV ntpd, root dispersion is pulled down to 1000us, and
increments at 15us/s. No matter what, rootdisp does not go below 1ms.

[root at n1g ntpq]# ./ntpq -crv
associd=0 status=011d leap_none, sync_pps, 1 event, kern,
version="ntpd 4.2.7p253 at 1.2483 Sat Jan 28 11:01:39 UTC 2012 (1)",
processor="x86_64", system="Linux/3.1.8-2.fc16.x86_64", leap=00,
stratum=1, precision=-23, rootdelay=0.000, rootdisp=1.000, refid=PPS,
reftime=d2ceed35.e7967bf1  Sat, Jan 28 2012 21:55:01.904,
clock=d2ceed38.1b41ac47  Sat, Jan 28 2012 21:55:04.106, peer=60158, tc=3,
mintc=3, offset=-0.000, frequency=38.361, sys_jitter=0.001,
clk_jitter=0.000, clk_wander=0.000, tai=34, leapsec=201207010000,
expire=201212280000


Is this by design, or an oops? I stumbled upon it and though 'this might
not be right'.

The machine is 217.198.219.99 / 2002:d9c6:d896:ff05:21c:c4ff:fe10:7ba.

/Kasper Pedersen

------------------
driftfile /var/lib/ntp/drift
restrict default nomodify notrap nopeer
restrict -6 default nomodify notrap nopeer
restrict 127.0.0.1
restrict -6 ::1
tos minsane 0

#the PPS source is 14 usec late compared to UTC. By design.
server 127.127.22.0 minpoll 3 maxpoll 3
fudge 127.127.22.0 flag2 0 flag3 1 time1 0.000014

#gpsd through SHM
server 127.127.28.1 minpoll 3 maxpoll 3 prefer true iburst
fudge 127.127.28.1 refid GPS time1 0.000044

server 192.168.9.3 minpoll 3 maxpoll 3 iburst

crypto digest sha1 host n1g ident n1g pw n1g
keysdir /etc/ntp/
includefile /etc/ntp/crypto/pw
keys /etc/ntp/keys
statistics clockstats loopstats peerstats
statsdir /var/log/ntpstats/

leapfile /etc/ntp/leap-seconds.3535228800
------------------------



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