[Mpi-22] mpi-22 Digest, Vol 2, Issue 7

[Quincey Koziol]

Hi Dick,

On Apr 23, 2008, at 11:00 AM, mpi-22-request_at_[hidden] wrote:
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 22 Apr 2008 13:38:03 -0400
> From: Richard Treumann <treumann_at_[hidden]>
> Subject: [Mpi-22] Another pre-preposal for MPI 2.2 or 3.0
> To: "MPI 2.2" <mpi-22_at_[hidden]>,
> 	<mpi-forum_at_[hidden]>
> Message-ID:
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> ON85257433.005C5199-85257433.0060DE25_at_[hidden]>
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>
>
> I have a proposal for providing information to the MPI  
> implementation at
> MPI_INIT time to allow certain optimizations within the run.  This  
> is not a
> "hints" mechanism because it does change the semantic rules for MPI  
> in the
> job run.  A correct "vanilla" MPI application could give different  
> results
> or fail if faulty information is provided.
>
> I am interested in what the Forum members think about this idea  
> before I
> try to formalize it.
>
> I will state up front that I am a skeptic about most of the MPI Subset
> goals I hear described.  However, I think this is a form of  
> subsetting I
> would support.  I say "I think" because it is possible we will find  
> serious
> complexities that would make me back away.. If this looks as
> straightforward as I expect, perhaps we could look at it for MPI  
> 2.2.  The
> most basic valid implementation of this is a small amount of work  
> for an
> implementer. (Well within the scope of MPI 2.2 effort / policy)

        I'm with you on being skeptical about the subsetting efforts and I'm  
also concerned about the proposal you have outlined.  The reason I'm  
concerned about both ideas is that they both don't seem to take  
adequate account of how to handle third-party software libraries that  
use MPI calls. Even if the third-party library is open source, I don't  
think most users of those libraries are going to trace through the  
source code to make certain of what MPI features the library uses.   
(Plus those features can easily change over time).  I suppose it's  
possible to ask third-party library providers to publish their  
"conformance" about which semantics can be relaxed, but I think that's  
going to be quite a burden for them.

        Quincey Koziol
        The HDF Group