RS: [Beowulf] Sempron compile optimization

[Greg Lindahl]

On Tue, Nov 29, 2005 at 03:40:04PM +1100, Chris Samuel wrote:

> Don't get me wrong, I've been able to build 64-bit versions of NAMD and 
> various other codes on SLES9 on PPC64 successfully, but I am suprised that 
> it's not fully native 64-bit.  I certainly was under the impression it was.

That depends on what "native" means. SGI shipped 64-bit OSes where
most of the binaries were 32-bit. The only reason Opteron OSes are
64-bit is because of the extra registers in 64-bit mode, meaning that
most programs are faster as 64-bit programs. Our compiler is a 32-bit
app because it uess a lot of pointers, and so the speed hit of fewer
registers is more than made up with less cache busting.

Both gcc and our compiler really support 64-bit compilation from a
32-bit compiler executable, so it's not actually "cross compiling".

-- greg