[Beowulf] CCL:Experiences with 64 bits AMD processors (fwd from marc@klingon.uab.es)

Greg Lindahl lindahl at pathscale.com
Sun Jun 20 00:08:39 PDT 2004


On Fri, Jun 18, 2004 at 09:53:23AM +0100, James Cownie wrote:

> Note, too, that for SPEC submissions on some of the other machines
> which can execute in both 32 and 64 bit modes the vendors have chosen
> to submit some results compiled in each mode to get the best overall
> performance. (The Alpha springs to mind here).

A more relevant example might be the... Opteron. Check out its SPEC
submissions. PathScale's submission uses -m32 for 1 fp code (art,
which is written in C) and 3 int codes (mcf, parser, and twolf, all
C).  gcc submissions do the same thing for int.

However, the generalization that 64-bit mode is almost always faster
is pretty true. And it's fairly hard to write a Fortran code that uses
that many pointers.

-- greg





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