[Beowulf] Alternative to MPI ABI

Patrick Geoffray patrick at myri.com
Fri Mar 25 11:59:18 PST 2005

Hi Greg,

Greg Lindahl wrote:
> I think this overall idea falls short of the benefit of an ABI for a
> couple of reasons. The first is that it's unlikely to get wide
> distribution if it doesn't come with MPI implementations. The second
> is that it's harder to maintain "out of tree"; the minute that an MPI
> implementation changes something, MorphMPI is going to be broken.

I don't see it that way. First, the implementations of the translation 
layers will be done by each MPI implementations. MorphMPI (no offense 
Jeff but we got to choose a somewhat cooler name) just define the common 
interface, nothing more. If the common layer does not change, the 
translation does not have to change unless something in the  side of the 
MPI implementation changes, and its maintainer should then keep its 
local translation layer up to date.

> Was there a big fight over the Fortran interface? It nails down the
> types because it has to. All the ABI does is make C look like Fortran;
> no internals need change in any implementation.

You don't change internals, you translate them. Let say you use pointers 
in your MPI implementation and the common layer specifies integers. In 
your translation layer, you translate pointers into integers by putting 
them in a table. You have as much work as your internals are far from 
the common interface and, hopefully, it will be a midpoint for everybody.


Patrick Geoffray
Myricom, Inc.

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