[ntp:questions] Red Hat vote for chrony

Paul tik-tok at bodosom.net
Sun Dec 7 20:47:12 UTC 2014


On Sun, Dec 7, 2014 at 2:42 PM, Charles Swiger <cswiger at mac.com> wrote:

> I would agree with this point if it were applicable.
>

In fact it is as others have tried to point out to you.


... Heck, even today's modern smartphone has an
> AGPS chip and more horsepower than a ~2002-era Soekris with an embedded
> CPU.
>

I have no idea what you're talking about but "horsepower" is not relevant.


> If you want to use PTP for timestamping, rather than a PPS signal over a
> GPIO pin, parallel/serial port, fine.  What PTP time source did you have
> in mind?
>

As as been pointed out to you by others you can't measure error using the
network unless you remove the network error.  That's why you would use PTP
but as also noted measuring across the network is the wrong answer.  I
wasn't suggesting using PTP.  I said it tries to solve "*one* of the tings
you have to deal with".


> > Maybe you're also unfamiliar with what NTP is doing:  It disciplines a
> virtual (system) clock which is derived from the on-board (usually
> uncompensated) crystal.
>
> I've been providing NTP stratum-1 or -2 timeservice to the public since
> the late 80's.
>
>
> Nevertheless, you're welcome to patronize me about my limited knowledge of
> NTP if you
>
at least have a productive point to make by doing so.
>

 And I've been doing it
since you could peer with fuzzballs.  Driving to work every day for 30
years doesn't make you an automotive engineer.

>  The big problem is temperature induced wander and that's something (back
> to RedHat and Chrony) Chrony claims to do better.
>
> Yes, ntpd and chrony will notice temperature changes causing a frequency
> drift,
>

You don't need to repeat approximately what I said back to me.


Back to your favorite source: <http://phk.freebsd.dk/time/20141026.html>
but you won't read it so:

"The reason most crystals don't behave that way, is that people usually
don't put a 100W variable heating element right next to them.
If you look at the horizontal part, you can see a lot of small wiggles,
that is the aircondition cycling on and off.
Around 5000 seconds, there's a dip, that's me using the machine to crunsh a
couple of gigabytes of data, and the heat from the CPU affects the crystal."

The 100W heater is the CPU by the way.

And as long I we're providing pointless qualifications:

If a $1500 PRS-10 is out-of-bounds even for measurement purposes against a
~$250 embedded system + GPS puck


I have a PRS-10 and s GPSD(D)OCXO system.  I even have a decent counter and
scope.  I didn't say it was out of bounds for measurement I said the
opposite.  Are you one of those opposite guys?  If I say X are you going to
say I said not-X?

This started when you said:

"Without measuring the
local clock against some other clock or oscillator which is known to be
accurate to sub-microsecond levels, one doesn't have the data needed to draw
conclusions about the actual timekeeping precision."

I (sort of) agree with you but nothing you've said addresses that issue.
But you don't have to believe me.  Just pay attention to any of the people
that have tried to point out your errors.


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