I have created a ticket for it. http://trac.mpich.org/projects/mpich/ticket/2049 Rajeev On Feb 28, 2014, at 8:13 AM, Carsten Clauss <[email protected]> wrote:

Constantly, our users step into the common trap of aliasing send and receive buffers e.g. in (All)Gather(v) instead of using MPI_IN_PLACE.

Although these cases are frequently caught by lower-level memcpy() checks within MPICH, I wonder if it would be feasible to do so already in the upper MPI layer, e.g. by using MPIR_ERRTEST_ALIAS_COLL() in a more comprehensive manner.

IMHO it would be nice to extend the check e.g. in MPI_(All)Gather() from

/* catch common aliasing cases */ if (recvbuf != MPI_IN_PLACE && sendtype == recvtype && sendcount == recvcount && sendcount != 0) MPIR_ERRTEST_ALIAS_COLL(sendbuf,recvbuf,mpi_errno);

-- that would only take effect for root=0 -- to let's say:

/* catch common aliasing cases */ MPID_Datatype_get_size_macro(recvtype, recvtype_size); if (recvbuf != MPI_IN_PLACE && sendtype == recvtype && sendcount == recvcount && sendcount != 0) MPIR_ERRTEST_ALIAS_COLL(sendbuf, (char*)recvbuf + comm_ptr->rank*recvcount*recvtype_size, mpi_errno);

And the same for MPI_(All)Gatherv() (which currently do not check for aliasing at all):

/* catch common aliasing cases */ MPID_Datatype_get_size_macro(recvtype, recvtype_size); if (sendbuf != MPI_IN_PLACE && sendtype == recvtype && recvcounts[comm_ptr->rank] != 0 && sendcount != 0) MPIR_ERRTEST_ALIAS_COLL(sendbuf, (char*)recvbuf + displs[comm_ptr->rank]*recvtype_size, mpi_errno);

I think this would lead to much more understandable error messages ("PMPI_Gatherv(363): Buffers must not be aliased" vs. "memcpy argument memory ranges overlap") -- or is there something that speaks against this kind of checks?

With kind regards, C. Clauss

-- Carsten Clauss Possartstrasse 20 D-81679 Muenchen www.par-tec.com _____________________________________ ParTec Cluster Competence Center GmbH

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