Re: [chrony-dev] [GIT] chrony/chrony.git branch, master, updated. 1.26-26-g9a01ccc

[Bill Unruh <unruh@xxxxxxxxxxxxxx>]

On Wed, 16 Nov 2011, Miroslav Lichvar wrote:

> On Tue, Nov 15, 2011 at 02:25:09PM -0800, Bill Unruh wrote:
> > > http://mlichvar.fedorapeople.org/tmp/chrony_corr2.png
> >
> > Are those two separate realisations of the random process which perturb the
> > offset and rate, or are they the same? It might be an idea to use exactly the
> > same one for both so one can see better what the difference is. (Yes, I
> > recognize that the key difference is that the green curve is smoother than the
> > red curve which is a good thing, but other details are harder to separate out.
>
> Running two clients in exactly the same conditions is a bit tricky do
> to in the simulator. The NTP server and NTP client run in parallel, as
> the clknetsim server uses the same system random() for all clients and
> they pick numbers from the sequence in a random order, it's very
> unlikely to have a deterministic simulation. The sequences for the
> clock frequency and the network delays in each direction have to be
> pregenerated to files and clknetsim configured to read them instead of
> using the random generator.
>
> Here is a new simulation with the default corrtimeratio and the same
> random sequences used for both NTP clients:
> http://mlichvar.fedorapeople.org/tmp/chrony_corr3.png

Ah, OK, it maily smooths out the very short term jumps -- ie, as if a low pass
filter had been run over the data.

I assume that if you used a higher corrtimeratio you would get further
smoothing. The question is whether with that same data you would also begin to
get evidence of oscillations as well with that same dataset


> Here is the uncorrected clock frequency if you want to see how it
> correlates to the offset oscillations:
> http://mlichvar.fedorapeople.org/tmp/chrony_corr3_clk.png

--
William G. Unruh   |  Canadian Institute for|     Tel: +1(604)822-3273
Physics&Astronomy  |     Advanced Research  |     Fax: +1(604)822-5324
UBC, Vancouver,BC  |   Program in Cosmology |     unruh@xxxxxxxxxxxxxx
Canada V6T 1Z1     |      and Gravity       |  www.theory.physics.ubc.ca/

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