Confused about CLOCK_TICK_RATE

[Timur Tabi]

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?

-- 
Timur Tabi
Linux kernel developer at Freescale