Confused about CLOCK_TICK_RATE

[Scott Wood]

On Thu, Mar 12, 2009 at 02:01:00PM -0500, Timur Tabi wrote:
> Can someone explain CLOCK_TICK_RATE to me?  It's defined in
> arch/powerpc/include/asm/timex.h as such:
> 
> #define CLOCK_TICK_RATE	1024000 /* Underlying HZ */
> 
> Every architecture defines this, but some use the better comment
> "Underlying frequency of the HZ timer".
> 
> My question is: why is this a constant? Shouldn't it be a variable,
> perhaps something that is based on tb_ticks_per_usec?

Looks like legacy crud, originally meant to be the PIT input frequency, that
isn't used for much on powerpc.  It was probably chosen so as to make HZ ==
ACTHZ for the supported values of HZ.

-Scott