Testing ntpd and/or timing from gpsd

[Eric S. Raymond]

Hal Murray <hmurray at megapathdsl.net>:
> You can use a Pi with GPS to monitor other systems, but the Ethernet on USB 
> that limits the resolution of what you can measure.  It's probably good 
> enough for watching sites on the Internet and/or your ISP connection.  It's 
> probably not good enough if you are interested in the difference due to using 
> the kernel PLL.

I'm planning to use the test farm to address that question.  The idea
is: configure two Pi 3s identically, except that one ntpd build has
KERNEL_PLL disabled. Probably the easiest way to arrange this will also
be closest to the real-world case: benchmark refclock 20 against
28 being fed by gpsd.

Run them in paallel for a couple days after they stabilize, collecting
*mumble* statistics.  Compare statistics to see if we can see evidence
of any accuracy gain above the noise floor.

The main reason I haven't tried this already (other than being swamped with
other tasks) is that I don't know what the value of *mumble* ought to be.
What statistics should we collect?  What figure(s) of merit do we look
for after the test run?

I need a pretty detailed answer to this question before we can move forward
on this front.  Please consider it carefully and bring the full weight of
your expertise to bear.
-- 
		<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>