[Cialug] Opteron and 64 bit architecture question

[Aaron Porter]

On 4/26/05, Nathan C. Smith <smith@ipmvs.com> wrote:
> My question is, if you run a 32 bit program on a 64 bit machine
> (particularly AMD), does it have to recreate this memory access kludge in
> the "emulation mode", or is this one of the ways it can give a little boo=
st
> to a 32 bit system running on a 64 bit architecture.

The "kludge" was for the OS to access more than 4gb, your applications
were generally still limited to under 4.

> If I buy 64 bit machines now, and run 32 bit Oss on them, I will be
> future-proofed to some degree, but will I get any benefit for the 32 bit =
OS
> today?

Yes, but mainly from the memory hardware. AMD's HyperTransport kicks
the pants off Intel's stuff.

> Anyone with an Opteron happy with it in 64 or 32 bit "mode"?  I have an
> Athlon 64 Machine at work running Fedora Core 3 64.  It is a fast machine=
,
> but I can't say that is is significantly faster than other machines,
> subjectively, it actually "felt" faster running 32 bit FC3.

I've got ~150 dual cpu opterons running Debian Sarge i386 with a
home-brew amd64 kernel. The vast majority of our apps are 32bit
binaries, and the developers are months away from starting the
(trivial) process of recompiling. We've seen anything from a 30-80%
speed increase in run time (Opteron 246 @ 2ghz vs Xeon @ 2.2ghz) on
the same binarires simply because of the faster memory bus. Night and
day for most of our stuff.

We've also got Debian Sid amd64 running on a few of our larger boxes
and desktops, and it's  been rock solid. Nothing more satisfying than
watching a $10k amd64/debian box spank a $50k sun box.