[LinuxPPS] Experiments with HZ

[Hal V. Engel]

On Monday 13 October 2008 09:31:38 clemens at dwf.com wrote:
> > Hi,
> >
> > Has any one experimented with different HZ values and NTP performance ?
>
> Yes.
> Stick with 100Hz.
> The kernel has some ntp stuff in it, but the time constants there are ONLY
> for 100Hz.  When I tried 1000Hz, instead of the time offset closing in on
> zero exponentially, it oscillated with a large amplitude, for days around
> the correct
> value.
>
> So, the kernel either needs a set of time constants for each of the current
> 4 choices for Hz, or (better) some side calculation of the time constants
> dependent on what Hz is chosen.
>
> Till that happens, use 100Hz.
> -- 
>                                        Reg.Clemens
>                                       reg at dwf.com

I also tried different tick intervals and came to the same conclusion as Reg,  
With the current Linux kernels 100Hz will give you the most stable time 
keeping.  In addition to 1000Hz I also tried 300Hz but I am now running at 
100Hz.  I found a thing on-line where the user was using freeBSD and he 
recommend 1000Hz but I suspect that the freeBSD kernel is a little more mature 
than the Linux kernel when it comes to this stuff. 

Hal