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Subject: Re: [OMPI users] Prototypes for Fortran MPI_ commands using 64-bit indexing
From: Jeff Squyres (jsquyres) (jsquyres_at_[hidden])
Date: 2013-10-30 18:29:24


Can you send the information listed here:

    http://www.open-mpi.org/community/help/

On Oct 30, 2013, at 6:22 PM, Jim Parker <jimparker96313_at_[hidden]> wrote:

> Jeff and Ralph,
> Ok, I downshifted to a helloWorld example (attached), bottom line after I hit the MPI_Recv call, my local variable (rank) gets borked.
>
> I have compiled with -m64 -fdefault-integer-8 and even have assigned kind=8 to the integers (which would be the preferred method in my case)
>
> Your help is appreciated.
>
> Cheers,
> --Jim
>
>
>
> On Wed, Oct 30, 2013 at 4:49 PM, Jeff Squyres (jsquyres) <jsquyres_at_[hidden]> wrote:
> On Oct 30, 2013, at 4:35 PM, Jim Parker <jimparker96313_at_[hidden]> wrote:
>
> > I have recently built a cluster that uses the 64-bit indexing feature of OpenMPI following the directions at
> > http://wiki.chem.vu.nl/dirac/index.php/How_to_build_MPI_libraries_for_64-bit_integers
>
> That should be correct (i.e., passing -i8 in FFLAGS and FCFLAGS for OMPI 1.6.x).
>
> > My question is what are the new prototypes for the MPI calls ?
> > specifically
> > MPI_RECV
> > MPI_Allgathterv
>
> They're the same as they've always been.
>
> The magic is that the -i8 flag tells the compiler "make all Fortran INTEGERs be 8 bytes, not (the default) 4." So Ralph's answer was correct in that all the MPI parameters are INTEGERs -- but you can tell the compiler that all INTEGERs are 8 bytes, not 4, and therefore get "large" integers.
>
> Note that this means that you need to compile your application with -i8, too. That will make *your* INTEGERs also be 8 bytes, and then you'll match what Open MPI is doing.
>
> > I'm curious because some off my local variables get killed (set to null) upon my first call to MPI_RECV. Typically, this is due (in Fortran) to someone not setting the 'status' variable to an appropriate array size.
>
> If you didn't compile your application with -i8, this could well be because your application is treating INTEGERs as 4 bytes, but OMPI is treating INTEGERs as 8 bytes. Nothing good can come from that.
>
> If you *did* compile your application with -i8 and you're seeing this kind of wonkyness, we should dig deeper and see what's going on.
>
> > My review of mpif.h and mpi.h seem to indicate that the functions are defined as C int types and therefore , I assume, the coercion during the compile makes the library support 64-bit indexing. ie. int -> long int
>
> FWIW: We actually define a type MPI_Fint; its actual type is determined by configure (int or long int, IIRC). When your Fortran code calls C, we use the MPI_Fint type for parameters, and so it will be either a 4 or 8 byte integer type.
>
> --
> Jeff Squyres
> jsquyres_at_[hidden]
> For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/
>
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-- 
Jeff Squyres
jsquyres_at_[hidden]
For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/