ntpd goes into oscillation
unruh
18 LVC PPS via shm. The oscillation has a period of just under an hour (
about 50 min) and an amplitude of about 10usec. in the offsets (
amplitude of about .005PPM in the rate). Since this is acting as the
clock for a number of other machines, they are also showing the
oscillation especially in the rate.
While I suppose this could be something in the GPS itself, it looks more
like an oscillation in ntpd.
Nothing changed when the oscillations started. Ntpd had been started
on Dec 14, and this change began on Dec24.
You can see the graph on www.theory.physics.ubc.ca/chrony/chrony.html ,
the graph for the machine called string.
Has anyone else ever seen this kind of thing?
David J Taylor
news:slrnhjkta6...@wormhole.physics.ubc.ca...
Something similar, perhaps, yes, and I reported it here before.
It seems that NTP hits the +/- 500 ppm drift limit and can't recover -
check the drift file contents. You might try deleting (or renaming) the
drift file. I haven't seen this for some time, though. What version are
you running?
Cheers,
David
Hal Murray
What OS? (version?)
What is the temperature like?
If you feed a sawtooth into a PLL, the offset will be the derivative,
a square wave. The amplitude of the square wave is smaller with
higher gain. A sawtooth with a 1 hour period is possible from
air conditioners.
I've seen oscillations on boxes using the pool, or at least stuff
that looks like oscillations to my eyeball. That's on Linux.
(They have been "fixing" the timekeeping code. I wouldn't be
surprised by anything.)
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unruh
Nope, the drift is NOT at the limit ( it is at about 200)
ntp 2.4.2p4
>
> Cheers,
> David
>
unruh
> In article <slrnhjkta6...@wormhole.physics.ubc.ca>,
> unruh <un...@wormhole.physics.ubc.ca> writes:
>>ntpd has suddenly broken out into oscillations. it is fed by a Garmin
>>18 LVC PPS via shm. The oscillation has a period of just under an hour (
>>about 50 min) and an amplitude of about 10usec. in the offsets (
>>amplitude of about .005PPM in the rate). Since this is acting as the
>>clock for a number of other machines, they are also showing the
>>oscillation especially in the rate.
>>While I suppose this could be something in the GPS itself, it looks more
>>like an oscillation in ntpd.
>>Nothing changed when the oscillations started. Ntpd had been started
>>on Dec 14, and this change began on Dec24.
>>You can see the graph on www.theory.physics.ubc.ca/chrony/chrony.html ,
>>the graph for the machine called string.
>>
>>Has anyone else ever seen this kind of thing?
>
> What OS? (version?)
Linux-- Mandriva 2008.1 ( kernel 2.6.24.7-desktop-3mnb)
This oscillation has just started.
>
> What is the temperature like?
The temp should be relatively stable ( certainly no air conditioner, although
possibly cooler than usual because the heating has been turned down for
the Christmas break-- After all nothing happens in the University during
Christmas. Research-- what's that?.
HOwever it so happens that I have the internal temp recorded via
lmsensors for the past 5 days, and there is some evidence of a one
degree flucutation (the resolution of the onboard thermometers)
with about the same period. No idea what that is,
since there is no airconditioning/heating. But I suppose it could be
causing that fluctuation in the rate and thus the offset.
Which somehow started on Dec 24.
Lets see what happens when classes begin again next week.
>
> If you feed a sawtooth into a PLL, the offset will be the derivative,
> a square wave. The amplitude of the square wave is smaller with
> higher gain. A sawtooth with a 1 hour period is possible from
> air conditioners.
Actually, no, the offset is the integral, not the derivative, of the
drift, so the offset will be a bunch of peaks.
>
>
> I've seen oscillations on boxes using the pool, or at least stuff
> that looks like oscillations to my eyeball. That's on Linux.
> (They have been "fixing" the timekeeping code. I wouldn't be
> surprised by anything.)
Yes, but then this "fix" whatever it is, has been the same for months now.
>
Richard B. Gilbert
You could get a better answer by supplying better information!
Your message did not mention what hardware platform you are running ntpd
on nor the operating system, the versions of the O/S and NTPD, etc, etc!
The contents of ntp.conf are important but you have neglected to post
this as well.
Please see http://www.catb.org/~esr/faqs/smart-questions.html
and try again.
Danny Mayer
> The temp should be relatively stable ( certainly no air conditioner, although
> possibly cooler than usual because the heating has been turned down for
> the Christmas break-- After all nothing happens in the University during
> Christmas. Research-- what's that?.
I don't know about UBC but we always got a lot of research done exactly
at times like that during the holidays. After all there weren't any
students around to teach.
Danny
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