Benchmarks: AMD64 vs i386 on Dual 246 Opteron

[Steve Kargl]

On Thu, Jul 28, 2005 at 09:23:38AM -0700, ray at redshift.com wrote:
> | 
> | Drop 8 GB of memory into the box and see how the 32-bit
> | FreeBSD performs in comparison to the 64-bit FreeBSD
> | when your process consumes greater than 4GB of memory.
>
> True, once you go over the 4GB limit it's a different ball of wax.
> However, until that time, it would be nice to get to the bottom of
> why 64 bit code is running half the speed of 32 bit code on the exact
> same machine - don't you think?

Well, I have 12 GB of memory and run numerical intensive codes
that easily can grab 4+ GB, so I've never explored i386 FreeBSD on
an amd64 system.  

As mentioned elsewhere, I would look for optimizations within
the software packages that target i386.  Additionally, the
instruction schedulers in gcc/gas have had many more years
of development in comparison to the amd64 schedulers.

An interesting test would be to build math/atlas on 32-bit
and 64-bit FreeBSD and then run some linpack benchmarks.

-- 
Steve