Thanks for your reply.

I inquired the same of PGI.  Dave Borer, PGI Customer Service Manager, responded:

 I believe -fast and -fastsse are identical for 64-bit compilers, but there are some differences
with 32-bit compilers.  I don't think TCP/IP based MPI routines have better performance from
optimizations, unless the processes are all running on the same machine.   I will ask engineering
how messages are passed when all the processes are running on the same hardware.

I am running on a 64-bit machine; I used -fast.

Larry Baker
US Geological Survey

On 19 May 2011, at 6:21 PM, Jeff Squyres wrote:

On May 18, 2011, at 8:32 PM, Larry Baker wrote:

The PGI compilers have a -fast and a -fastsse option.  Does OpenMPI make effective/safe use of SSE instructions (block moves maybe?)?  

Not really.  The biggest thing that we do that can take advantage of vector instructions is memcpy, *mostly* in the shared memory transport, but also if your MPI application hap some funky non-contiguous MPI datatypes, too.

On their web site, PGI uses -fast in their examples for OpenMPI rather than -fastsse.  I don't know why.

Maybe for more portability...?

Jeff Squyres
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