[Beowulf] Win64 Clusters!!!!!!!!!!!!

[Greg Lindahl]

On Mon, Apr 09, 2007 at 09:04:21AM -0700, Michael Will wrote:

> I saw Spec benchmarks published with portions of it compiled for
> 32bit for best results. But the bottom line is that default in 64bit
> is faster and some special cases could benefit from 32bit...

Oh, you want a *serious* answer!

I don't know for SPECcpu2006, but with SPECcpu2000, a couple of the
integer benchmarks ran faster in 32-bit, and none of the floating
point benchmarks.

Our compiler run 2x faster as a 32-bit binary, because it has very bad
cache behavior when pointers get twice as large -- it uses a lot of
them.

But the general rule is that code is 15% faster in 64-bit, thanks to
the extra registers and better calling convention. And a few codes
(especially multi-precision integer codes like crypto) benefit from
64-bit integers.

-- greg