On Sat, Jan 28, 2012 at 22:02, Kasper Pedersen <[email protected]> wrote: > > 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@n1g ntpq]# ./ntpq -crv > associd=0 status=011d leap_none, sync_pps, 1 event, kern, > version="ntpd [email protected] 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'.
This is by design. ChangeLog has under 4.2.7p237: * Floor calculation of sys_rootdisp at sys_mindisp in clock_update (from Dave Mills). sys_mindisp is controlled by "tos mindist" and defaults to 1 millisecond: [1] http://www.eecis.udel.edu/~mills/ntp/html/miscopt.html#tos Cheers, Dave Hart _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
