On Tue, Mar 14, 2006 at 05:39:31PM -0500, Thor Lancelot Simon wrote:
> On Tue, Mar 14, 2006 at 12:57:01PM -0800, Garrett D'Amore wrote:
> > 
> > My understanding, from what others have said, is that the problem is
> > that function calls *in general* are expensive on a VAX.
> 
> And almost everywhere else, compared to a one or two instruction
> sequence to read across the bus.  Doing a function call every time
> you want a byte from the device is a pretty painful way to do PIO,
> unless your CPU is many orders of magnitude faster than some of the
> hardware people are still trying to use -- some of the hardware
> that's still being built and deployed today, even.
> 
> Indirect calls, on some CPUs, are even worse, because they defeat
> I-cache prefetch.

OK. Which CPUs? How much worse? (I'm not talking about com and bus_space
anymore).

Pavel