Re: [chrony-users] Timeout for initstepslew?

[Zack Shivers <zack@xxxxxxxxx>]

> I agree. But that also means that host2 will be slaved to host1 and if host1
> goes wandering off for some reason, host 2 will try to follow.

This is the intended behavior in my system. See my application description.

> The filter is for refclocks and is a "median" filter in which
> the stuff which is more than 1 standard devation away from the mean is thrown
> away. This is to try to get rid of "popcorn" noise.
> You are not using a refclock.

According to the 3.5 docs, I can specify a filter option along with
the server option. See
https://chrony.tuxfamily.org/doc/3.5/chrony.conf.html#server
"This option enables a median filter to reduce noise in NTP
measurements. The filter will reduce the specified number of samples
to a single sample. It is intended to be used with very short polling
intervals in local networks where it is acceptable to generate a lot
of NTP traffic."

On Tue, Sep 24, 2019 at 2:14 PM Bill Unruh <unruh@xxxxxxxxxxxxxx> wrote:
>
>
> On Tue, 24 Sep 2019, Zack Shivers wrote:
>
> > Going back to my terminology, host1 is the NTP server, host2 is the NTP client. My understanding is that host1's clock will not change in
> > response to anything in host2 since there is a unidirectional relationship between server and client. There can be no feedback loop if this is
> > true.
>
> I agree. But that also means that host2 will be slaved to host1 and if host1
> goes wandering off for some reason, host 2 will try to follow.
>
> chrony does better than ntpd at trying to smooth out the response because of
> its fitting proceedure.
> The filter is for refclocks and is a "median" filter in which
> the stuff which is more than 1 standard devation away from the mean is thrown
> away. This is to try to get rid of "popcorn" noise.
> You are not using a refclock.
> Maybe you should us for example a gps timing receiver which one or both
> systems could use to discipline themselves to UTC.-- if both are slaved to
> utc, they are also slaved to each other.
>
>
> > Could I gain the accuracy of shorter polling interval with added rate stability by using the filter option? If so, do you have any recommended
> > values for poll and filter?
> >
> >
> >
> > On Tue, Sep 24, 2019 at 12:10 PM Bill Unruh <unruh@xxxxxxxxxxxxxx> wrote:
> >       Actually setting a high poll rate does not necessarily get you a better sync.
> >       It determines the offset more "accurately" but determines the rate worse. Ie,
> >       if clock A gets its time from clock B, then the rate of A will jump around
> >       much more if the poll interval is shorter. Now you may not care about the
> >       clock rate, in which case short poll intervals are better, but that would also
> >       mean that time differences would be much more random. Also if you lose clock
> >       B, then clock A will drift away from the "correct" time much more rapidly.
> >
> >       Also, if in the short term, clock B say heats up (due to some program running
> >       on B) A will try to follow that change in timing on the short term.
> >
> >       Ie, you need to think carefully about what you want from your clocks, before
> >       you simply say "shorter poll intervals are better".
> >
> >       You could also set up a polling of the computer running B and only start
> >       chronyon A when B actually comes up.
> >
> >       What do you use for timing clock B? If B uses A as its source and A uses B,
> >       you can get problems with runaway behaviour. B tells A to speed up. A then
> >       tells B to speed up, and way they go.
> >
> >
> >       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/
> >
> >       On Tue, 24 Sep 2019, Zack Shivers wrote:
> >
> >       > Good to know these are equivalent!
> >       >
> >       > If I used this config, it will permanently set the poll rates for this
> >       > server, correct? Since this is a local setup, I'm using a high poll
> >       > rate (-3) to get a better sync. Setting the timeout as a function of
> >       > the poll rate is not ideal.
> >       >
> >       >
> >       >
> >       > On Tue, Sep 24, 2019 at 12:55 AM Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:
> >       >>
> >       >> On Mon, Sep 23, 2019 at 05:20:12PM -0700, Zack Shivers wrote:
> >       >>> I ask about the timeout on initstepslew is that the problem would be
> >       >>> solved if I could set a much longer timeout than 10 seconds. The
> >       >>> makestep option could work instead, but I've seen issues using this as
> >       >>> well that I will post about later.
> >       >>
> >       >> initstepslew is basically the same as a "server ... iburst" and
> >       >> "makestep" together. iburst in initstepslew will send up to 6 requests
> >       >> in 2 second interval, which is about 10 second total. If you need to
> >       >> send more requests and keep the short interval, you could use the minpoll
> >       >> and maxpoll options instead of iburst. For example:
> >       >>
> >       >> server host1 minpoll 1 maxpoll 1
> >       >> makestep 0.1 3
> >       >>
> >       >> Please let us know what are the issues with this approach.
> >       >>
> >       >> --
> >       >> Miroslav Lichvar
> >       >>
> >       >> --
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> >       >>
> >       >
> >       >
> >       > --
> >       >
> >       > Zack Shivers
> >       > Electrical / Embedded Systems Engineer
> >       >
> >       > --
> >       > To unsubscribe email chrony-users-request@xxxxxxxxxxxxxxxxxxxx
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> >       > For help email chrony-users-request@xxxxxxxxxxxxxxxxxxxx
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> >
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> > --
> > [uc?export=download&id=1wJzXSPmoblt1ldX71DDy4ceY-cHDQ-pa&revid=0B8gashE-Q-zgRi9zVElXTUNZRHhGWlczci9TdE5tMXN1K2hrPQ]
> > Zack Shivers
> > Electrical / Embedded Systems Engineer
> >
> >

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