FreeBSD 4.x Opteron Question

[Boris Spirialitious]

--- Chuck Robey <chuckr at chuckr.org> wrote:
> Boris Spirialitious wrote:
> > --- Boris Spirialitious <hardcodeharry at yahoo.com>
> > wrote:
> > 
> >>--- Matthew Seaman
> <m.seaman at infracaninophile.co.uk>
> >>wrote:
> >>
> >>>On Tue, Mar 15, 2005 at 08:50:22AM -0800, Boris
> >>>Spirialitious wrote:
> >>>
> >>>>When opteron support start for Freebsd? I have
> >>>
> >>>4.9. 
> >>>
> >>>>is supported? Or 4.11 better? I can't use 5.x.
> >>>
> >>>Well, AMD64 support as a tier-1 platform only
> came
> >>>in with 5.x, so
> >>>you're S.O.L. if you have to use a 4.x release
> >>>version.  
> >>> 
> >>>
> >>>>Will a i386 disk boot on opteron system? Can I
> >>>>use same disk image for intel and amd MBs? Any
> >>>>big problems?
> >>>
> >>>You can generally run AMD64 machines in IA32 mode
> >>
> >>--
> >>
> >>>but what would be
> >>>the point? All you get then is a machine that
> >>
> >>costs
> >>
> >>>more than an
> >>>equivalent IA32 box and that probably performs
> >>>worse.
> >>
> >>That is very curious to say. Isn't the advantage
> >>of Opteron the superior IO architecture? There is
> >>not much advantage with 64 bit computing. What is
> >>faster about it? Pointers are bigger, so it use
> >>more cache for less. NOt much 64bit math in
> >>OS. Why do you say it will perform worse?
> 
> Boris, I am sure you realize that a great deal of
> the 64 bit IO 
> architecture is leveraged from the 64 bit
> instructions set, that allows 
> things like 64 bit fetches.  Will there be a gain
> without using the 64 
> bit instruction set?  Yes.  Will it be as large? 
> No.

I do not see that. Most adapter card registers only
32bits, and PCIX dma is 64bits anyway, so what
64bit fetches are there? Larger pointers take
up more cache space. Benchmark show that 64bit
pointers slow memory operation. So the difference
overall may be small.

I not argue about 64bit maybe faster. But the 
hypertransport architecture may be enough to
make the cost worthwhile.

Boris


		
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