Re: Why HZ on i386 is 100 ?

[Matti Aarnio]

On Wed, Apr 17, 2002 at 02:01:42AM -0400, Robert Love wrote:
> On Wed, 2002-04-17 at 01:34, Linus Torvalds wrote:
> > No, it also makes it much easier to convert to/from the standard UNIX time
> > formats (ie "struct timeval" and "struct timespec") without any surprises,
> > because a jiffy is exactly representable in both if you have a HZ value
> > of 100 or 100, but not if your HZ is 1024.
> 
> Exactly - this was my issue.  So what _was_ the rationale behind Alpha
> picking 1024 (and others following)?  More importantly, can we change to
> 1000?

   Alpha processors don't have full division hardware, they have to
   iterate it one bit at the time. They do have a flash multiplier,
   and a barrel-shifter.  Shifts take one pipeline cycle, like to
   addition and substraction.  Multiply takes 6-12 depending on model,
   but division takes 64...

   Converting the  tick  to  gettimeofday()  seconds is faster when
   the tick is power of two.

> 	Robert Love

/Matti Aarnio