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Subject: Re: [OMPI devel] SSE instructions?
From: Larry Baker (baker_at_[hidden])
Date: 2011-05-19 21:46:34


Thanks for your reply.

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

> 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
> jsquyres_at_[hidden]
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