Determine MPI Data Types in col_on_comm() & dst_on_comm() to prevent displacements overflow. (Fix for #2156) #2157
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…displacements overflow. The MPI_Gatherv() and MPI_Scatterv() operations require integer displacements into the communications buffers. Historically everything is passed as an MPI_CHAR, causing these displacements to be larger than otherwise necessary. For large domain sizes this can cause the displace[] offsets to exceed the maximum int, wrapping to negative values. This change introduces additional error checking and then uses the function MPI_Type_match_size() (available since MPI-2.0) to determine a suitable MPI_Datatype given the input *typesize. The result then is that the displace[] offsets are in terms of data type extents, rather than bytes, and less likely to overflow.
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Just for awareness, I can't see the output of the failed |
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Common problem - it will be provided by message later
…On Fri, Jan 17, 2025 at 3:21 PM Benjamin S. Kirk ***@***.***> wrote:
Just for awareness, I can't see the output of the failed WRF-BUILD-2690;
I get a timeout accessing
https://ncar_jenkins.scalacomputing.com/job/WRF-Feature-Regression-Test/2690/console
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Fixes runtime failures caught by CI in in the underlying MPI_Gatherv().
Of course dtype needs to be MPI_Datatype, not an int. This error sneaked through MPICH-based tests but not OpenMPI. Hopefully this change will address previous CI failures.
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The regression test results: |
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@benkirk Thanks for the fix! I tested it for a few cases we could run before and it is working now. |
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Thanks for the success report @weiwangncar, happy to help! |
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Determine MPI Data Types in col_on_comm() & dst_on_comm() to prevent displacements overflow.
TYPE: bug fix
KEYWORDS: prevent displacements overflow in MPI_Gatherv() and MPI_Scatterv() operations
SOURCE: Benjamin Kirk & Negin Sobhani (NSF NCAR / CISL)
DESCRIPTION OF CHANGES:
Problem:
The MPI_Gatherv() and MPI_Scatterv() operations require integer displacements into the communications buffers. Historically everything is passed as an MPI_CHAR, causing these displacements to be larger than otherwise necessary. For large domain sizes this can cause the displace[] offsets to exceed the maximum int, wrapping to negative values.
Solution:
This change introduces additional error checking and then uses the function MPI_Type_match_size() (available since MPI-2.0) to determine a suitable MPI_Datatype given the input *typesize. The result then is that the displace[] offsets are in terms of data type extents, rather than bytes, and less likely to overflow.
ISSUE: Fixes #2156
LIST OF MODIFIED FILES:
M frame/collect_on_comm.c
TESTS CONDUCTED:
Failed cases run now.
RELEASE NOTE:
Determine MPI Data Types in col_on_comm() & dst_on_comm() to prevent displacements overflow.