[mpich-discuss] Checks for buffer aliasing in coll ops?

[Rajeev Thakur]

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 <c.clauss at fz-juelich.de> 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
> 
> Geschäftsführer RA. Dipl.-Ing. Bernhard Frohwitter Eingetragen beim
> Amtsgericht München HRB 151545 Steuer-Nr. 08/32305, Ust-ID DE235527064
> 
> _______________________________________________
> discuss mailing list     discuss at mpich.org
> To manage subscription options or unsubscribe:
> https://lists.mpich.org/mailman/listinfo/discuss