Re: [FLASH-USERS] 64 Bit FLASH on Opterons?

Hi everyone,

    I haven't tried compiling flash on an opteron yet, but I would be
curious to see if it compiles in 64-bit mode using GCC 4.0.2 (with
either the built-in gfortran or g95). GCC has had good AMD64 support
for a couple years now, and GCC 4 has an auto-vectorization option.

    One point I should make is that, in general, compiling for 64 bits
instead of 32 does not necessarily mean increased performance, only
access to more memory, with memory pointers that are twice as big. My
impression is that most modern hybrid (32/64-bit) CPUs provide the
same floating point capabilities and performance to both 32-bit and
64-bit codes.

- Nathan
  nhearn@uchicago.edu

On 1/2/06, Sebastian Heinz <heinzs@space.mit.edu> wrote:
> Hi all,
>
> Has anybody out there successfully compiled FLASH in 64 bit for
> Opterons? I can get it to run, but only 50% as fast as 32 bit and
> using twice the amount of ram for the same size problem - which I
> don't consider successful...
>
> I am using the PGI compilers (version 6) on SUSE 64 and MVAPICH
> (which I compile in 64 bit as well). The additional compiler flags I
> am using are -mcmodel=medium -tp k8-64 -Mlarge_arrays
>
> Thanks!
> Sebastian
>

--
Nathan C. Hearn
nhearn@uchicago.edu