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Subject: Re: [OMPI users] Pros and cons of --enable-heterogeneous
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2010-10-08 15:48:33


On Oct 8, 2010, at 2:21 PM, Jeff Squyres wrote:

> No. Open MPI does not have MPD -- I think you're thinking of a different MPI implementation. :-)

Someone pointed out to me off-list that I wasn't quite clear here...

*If* all of your architectures are the same endian and otherwise equivalent, you can just compile 32 bit and be ok. If your architectures are a mix of endians and/or other representations, you need the heterogeneous support.

Also note that there is a --hetero flag to mpirun that you will need to use. Here's the relevant bit from mpirun(1):

       --hetero
              Indicates that multiple app_contexts are being provided that are
              a mix of 32/64-bit binaries.

It seems a little klunky to have to specify --enable-heterogeneous in configure *and* specify --hetero on the command line, but as I mentioned, this is unfortunately not a common scenario and we therefore haven't really optimized it. :-\

I *swear* I just read in some of our documentation somewhere the part about mixing 32 and 64 bit MPI_DOUBLE (for example), but for the life of me, I can't find it now. :-(

-- 
Jeff Squyres
jsquyres_at_[hidden]
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