[LinuxPPS] 100hz versus 250hz kernel

[clemens at dwf.com]

> Folkert van Heusden wrote:
> > Hi,
> > 
> > Has anyone measured the stability for a 100hz and a non-100-hz kernel
> > (eg 250hz)?
> 
> Please add the NO_HZ thingie for 2.6.28 since that could help with the 
> 'slowness' of 100 Hz?
> 
This was discussed, at least slightly, several months ago when I was
having problems.

The net result was that the TIMEKEEPING KERNEL code needs different time constants
for different frequencies.  It would seem that FreeBSD (may) have these
time constants built in, but Linux definately doesnt.

My experiment was with 1000Hz, and the 'relaxaton' time for a step change
in the time/frequence (a restart) took forever (8-10Hrs) to drop exponentially
towards the 'right answer'.  

I sent a email to the person listed as taking care of this code in Linux,
but as far as I know, nothing has been done.

-- 
                                        Reg.Clemens
                                        reg at dwf.com