PLL (was Re: Objectives for the next year)

[Hal Murray]

esr at thyrsus.com said:
> I did.  There's a blog post about it:
> https://blog.ntpsec.org/2017/02/22/testframe-the-epic-failure.html 

>From there:
> One was what in discussion on the mailing list I later tagged "the code-path
> split". There are two kinds of NTP hosts; one uses a kernel facility known as
> the "PLL" for doing fine adjustments to the tick speed of the system clock,
> the other kind does not. Most of our potential deployment targets have PLLs;
> an undismissable minority do not. 

What do you mean by PLL?  Which systems don't have it?

A PLL requires 2 things.  One is a knob/switch to adjust something.  The other 
is sensor to compare something against a target setting and use that to 
control the knob.  A thermostat and heater is the normal example.

The kernels I'm familiar with have the knob but not the sensor.  They actually 
do have a sensor if you build the kernel with the right option but none of the 
distros I'm familiar with ship with that option enabled.

The bottom line is that every time you use "PLL" like that you toss a layer of 
confusion into the discussion.  (or at least my part of it)


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