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From: ktl@wag.caltech.edu (Kian-Tat Lim)
Newsgroups: comp.sys.sgi
Subject: Timeslave question
Message-ID: <1991Feb14.174728.16734@nntp-server.caltech.edu>
Date: 14 Feb 91 17:47:28 GMT
Sender: news@nntp-server.caltech.edu
Reply-To: ktl@wag.caltech.edu (Kian-Tat Lim)
Organization: California Institute of Technology, Pasadena, CA
Lines: 75
Nntp-Posting-Host: sgi1.wag.caltech.edu

We are using timeslave to track an NTP primary.  Assuming that the
'err' column in the debugging output is in units of milliseconds, we
seem to be off by as much as 1/4 second at times, both fast and slow,
though we're usually under 150 ms.  I have two questions:

1) Why doesn't timeslave do a better job?  The NTP host appears to
adjust its time by steps of 10 ms, as well as adjusting its clock
rate.  timeslave seems to have a hard time following the 10 ms jumps.
Should I be fiddling with some of the timeslave options to get better
tracking?  (It doesn't look like there's any control over the internal
filtering algorithm, unfortunately.)  I have also observed oscillatory
behavior, in which timeslave will overshoot the zero error point
(often by as much as it was off before) over and over.

2) Is there a bug in the timetrim computation?  It seems strange that
negative drifts (and -xx/yy sec/hr claims) end up with positive
timetrim values.

Maybe I should just give up and install xntp, but I was trying to get
decent time without the headaches of using yet another
vendor-unsupported package.

Here's an edited portion of our SYSLOG with -USR1 debugging:

Feb 13 16:39:36 sgi1 timeslave:     err exp-err     adj  drift    var
Feb 13 16:39:36 sgi1 timeslave:   -19.0   -17.8  -14.82 -0.058    7.4 b

[Constant at about -19 until:]

Feb 13 16:56:16 sgi1 timeslave:    -1.0   -19.3  -14.75 -0.058   18.3 b

[Wanders between -1 and -5 for a bit.  Why +1495 here?]

Feb 13 17:32:20 sgi1 timeslave: -0.206/137.39 or -0.220/1.01 sec/hr;
			 set timetrim=+1495 or -60368?

[Jump of +9.0]

Feb 13 18:17:53 sgi1 timeslave:    +4.0    -4.7  -14.65 -0.058   10.5 b

[Wanders around +4 for almost an hour, then steps up again]

Feb 13 18:54:14 sgi1 timeslave:   +13.0   +12.5  -13.48 -0.058    9.9 b

[And again, constant at about +13 till this step:]

Feb 13 19:42:26 sgi1 timeslave:   +23.0   +12.5  -12.62 -0.057   10.5 b

[Two more steps to +33 and +48 a few hours later, then a slow ramp to:]

Feb 14 04:18:54 sgi1 timeslave:   +90.0   +84.9   -4.16 -0.039    6.9 b
Feb 14 04:22:53 sgi1 timeslave:   +91.0   +84.7   -3.86 -0.039    7.0 b
Feb 14 04:26:47 sgi1 timeslave:   +92.0   +85.7   -4.26 -0.039    6.9 b

[Another step:]

Feb 14 04:30:54 sgi1 timeslave:  +102.0   +86.6   -3.69 -0.038   15.4 b
Feb 14 04:34:54 sgi1 timeslave:  +103.0   +96.4   -3.77 -0.038   14.7 b

[And another slow ramp up to:]

Feb 14 07:42:35 sgi1 timeslave:  +131.0  +123.2   +1.39 -0.025    9.8 b
Feb 14 07:46:44 sgi1 timeslave:  +132.0  +123.2   +1.94 -0.025    9.8 b

[Step:]

Feb 14 07:50:39 sgi1 timeslave:  +142.0  +124.1   +2.04 -0.025   17.9 b
Feb 14 07:50:39 sgi1 timeslave: +0.044/151.70 or +0.052/1.02 sec/hr;
			 set timetrim=-1650 or +2428?

[More ramp:]

Feb 14 09:11:52 sgi1 timeslave:  +154.0  +145.0   +4.54 -0.018   14.5 b
-- 
Kian-Tat Lim (ktl@wag.caltech.edu, KTL @ CITCHEM.BITNET, GEnie: K.LIM1)