[LinuxPPS] LinuxPPS comparable to FreeBSD here

[Miroslav Lichvar]

On Fri, Jun 18, 2010 at 12:25:24AM +0200, Remco dB wrote:
> Compared to my (also thermostatised) FreeBSD system (with hardpps) LinuxPPS 
> performs almost equally. 
> 
> See http remco.org/ntp

Interesting, what polling intervals are used?

> So I wonder, would adding hardpps _improve_ the LinuxPPS performance, 
> considering 'general hardware boundary conditions'?

That depends on the ratio between the PPS noise and the system clock
noise/wander. If you have a thermally stabilized crystal, switching to
kernel consumer (which is basically a FLL running at poll 0) will
probably not help. You might want to try different polling intervals
though.

FLL should perform better than PLL when the PPS signal has very low
jitter and/or the crystal temperature varies a lot (or it's a low
quality crystal).

You might also want to try chrony which uses a linear regresion model.
It usually performs better than both PLL and FLL.

-- 
Miroslav Lichvar