Kernel PPS processing

[Gary E. Miller]

Yo Matthew!

On Wed, 29 Jun 2016 14:55:23 -0400
Matthew Selsky <Matthew.Selsky at twosigma.com> wrote:

> On Wed, Jun 29, 2016 at 11:48:08AM -0700, Hal Murray wrote:
> > > Can you quantify the better?  I would have expected identical...  
> > 
> > Did you look at the graph?
> >   http://users.megapathdsl.net/~hmurray/ntpsec/glypnod-pps-kernel.png

Yeah, your 'No kernel' was aweful. If that is your baseline then you got
something really, really, wrong.  The scale on the 'kernel PLL' was too
small to really tell, but I think I get the same on my RasPi's.

Scroll down this:

    https://pi3.rellim.com/

Look at the 'offset of PPS'.  It shows usually better than +/- 15 microSec.
Looks like PPS is usually close to a few microSec, but frequent 20 microSec
dealsy.  I'm not sure what the daily spike is.

That is KPPS on git head of ntpsec and gpsd.

> We tested booting with "nohz=off intel_idle.max_cstate=0" and it made
> a difference in our production clocks.

But not kernel PPS?  I can see why the max_cstate might help, but if
the KPPS is interrupt driven I'm not sure why the nohz would help.

Can you quantify the individual effects?  And is that kernel PPS, KPPS
in ntpsec, or just PPS in ntpsec?

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588
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