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From: George Bosilca (bosilca_at_[hidden])
Date: 2006-02-10 18:10:38


Yvan,

I'm looking into this one. So far I cannot reproduce it with the
current version from the trunk. I will look into the stable versions.
Until I figure out what's wrong, can you please use the nightly
builds to run your test. Once the problem get fixed it will be
included in the 1.0.2 release.

BTW, which interconnect are you using ? Ethernet ?

   Thanks,
     george.

On Feb 10, 2006, at 5:06 PM, Yvan Fournier wrote:

> Hello,
>
> I seem to have encountered a bug in Open MPI 1.0 using indexed
> datatypes
> with MPI_Recv (which seems to be of the "off by one" sort). I have
> joined a test case, which is briefly explained below (as well as in
> the
> source file). This case should run on two processes. I observed the
> bug
> on 2 different Linux systems (single processor Centrino under Suse
> 10.0
> with gcc 4.0.2, dual-processor Xeon under Debian Sarge with gcc 3.4)
> with Open MPI 1.0.1, and do not observe it using LAM 7.1.1 or MPICH2.
>
> Here is a summary of the case:
>
> ------------------
>
> Each processor reads a file ("data_p0" or "data_p1") giving a list of
> global element ids. Some elements (vertices from a partitionned mesh)
> may belong to both processors, so their id's may appear on both
> processors: we have 7178 global vertices, 3654 and 3688 of them being
> known by ranks 0 and 1 respectively.
>
> In this simplified version, we assign coordinates {x, y, z} to each
> vertex equal to it's global id number for rank 1, and the negative of
> that for rank 0 (assigning the same values to x, y, and z). After
> finishing the "ordered gather", rank 0 prints the global id and
> coordinates of each vertex.
>
> lines should print (for example) as:
> 6456 ; 6455.00000 6455.00000 6456.00000
> 6457 ; -6457.00000 -6457.00000 -6457.00000
> depending on whether a vertex belongs only to rank 0 (negative
> coordinates) or belongs to rank 1 (positive coordinates).
>
> With the OMPI 1.0.1 bug (observed on Suse Linux 10.0 with gcc 4.0
> and on
> Debian sarge with gcc 3.4), we have for example for the last vertices:
> 7176 ; 7175.00000 7175.00000 7176.00000
> 7177 ; 7176.00000 7176.00000 7177.00000
> seeming to indicate an "off by one" type bug in datatype handling
>
> Not using an indexed datatype (i.e. not defining USE_INDEXED_DATATYPE
> in the gather_test.c file), the bug dissapears. Using the indexed
> datatype with LAM MPI 7.1.1 or MPICH2, we do not reproduce the bug
> either, so it does seem to be an Open MPI issue.
>
> ------------------
>
> Best regards,
>
> Yvan Fournier
> <ompi_datatype_bug.tar.gz>
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