[Mpi-forum] Error/gap in MPI_NEIGHBOR_ALLTOALL/ALLGATHER
rabenseifner at hlrs.de
Sat Sep 28 02:53:38 CDT 2019
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.
----- Anthony Skjellum <skjellum at auburn.edu> wrote:
> Rolf let’s open a Ticket
> Anthony Skjellum, PhD
> > 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 .
> > Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307) .
> > <neighbor_mpi-3_bug.pptx>
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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 .
Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307) .
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