[Mpi-forum] Error/gap in MPI_NEIGHBOR_ALLTOALL/ALLGATHER

[Skjellum, Anthony]

May iI open and assign to you preliminarily for at least the background and issue discussion (from emails) if not the solution?
You are welcome to pose the solution too, but you know, that's not required to get us started 🙂



Anthony Skjellum, PhD

Professor of Computer Science and Chair of Excellence

Director, SimCenter

University of Tennessee at Chattanooga (UTC)

tony-skjellum at utc.edu  [or skjellum at gmail.com]

cell: 205-807-4968


________________________________
From: mpi-forum <mpi-forum-bounces at lists.mpi-forum.org> on behalf of Rolf Rabenseifner via mpi-forum <mpi-forum at lists.mpi-forum.org>
Sent: Saturday, September 28, 2019 3:53 AM
To: Anthony Skjellum <skjellum at auburn.edu>
Cc: Rolf Rabenseifner <rabenseifner at hlrs.de>; Main MPI Forum mailing list <mpi-forum at lists.mpi-forum.org>; Simone Chiocchetti <simone.chiocchetti at unitn.it>; MPI-3 Collective Subgroup Discussions <mpiwg-coll at lists.mpi-forum.org>
Subject: Re: [Mpi-forum] Error/gap in MPI_NEIGHBOR_ALLTOALL/ALLGATHER

Yes, if after seven years of MPI_NEIGHBOR_ALLTOALL, neither the user know whether their MPI library is wrong nor all implementors are sure how to implement this routine for 1 or 2 processes in cyclic Cartesian direction, then some wording is missing in the MPI standard.

Best regards
Rolf

----- Anthony Skjellum <skjellum at auburn.edu> wrote:
> Rolf let’s open a Ticket
>
> Anthony Skjellum, PhD
> 205-807-4968
>
>
> > On Sep 27, 2019, at 6:09 PM, Rolf Rabenseifner via mpi-forum <mpi-forum at lists.mpi-forum.org> wrote:
> >
> > Dear MPI collective WG,
> >
> >    you may try to resolve the problem with a maybe wrong
> >    MPI specification for MPI_NEIGHBOR_ALLTOALL/ALLGATHER
> >
> > Dear MPI Forum member,
> >
> >    you may own/use an MPI implementation that implements
> >    MPI_NEIGHBOR_ALLTOALL/ALLGATHER
> >    with race conditions if #nprocs in one dimension is
> >    only 1 or 2 and periodic==true
> >
> > The problem was reported as a bug of the OpenMPI library
> > by Simone Chiochetti from DICAM at the University of Trento,
> > but seems to be a bug in the MPI specification,
> > or at least an advice to implementors is missing.
> >
> > I produced a set of animated slides.
> > Please look at them in presentation mode with animation.
> >
> > Have fun with a problem that clearly prevents the use
> > of MPI_NEIGHBOR_... routines with cyclic boundary condition
> > if one wants to verify that mpirun -np 1 is doing
> > the same as the sequential code.
> >
> > Best regards
> > Rolf
> >
> > --
> > Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de .
> > High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530 .
> > University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832 .
> > Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner<http://www.hlrs.de/people/rabenseifner> .
> > Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307) .
> > <neighbor_mpi-3_bug.pptx>
> > _______________________________________________
> > mpi-forum mailing list
> > mpi-forum at lists.mpi-forum.org
> > https://lists.mpi-forum.org/mailman/listinfo/mpi-forum

--
Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de .
High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530 .
University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832 .
Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner<http://www.hlrs.de/people/rabenseifner> .
Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307) .
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