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Subject: [OMPI devel] RFC: add support for large counts using derived datatypes
From: Nathan Hjelm (hjelmn_at_[hidden])
Date: 2013-07-16 15:14:28


What: Add support for the MPI-3 MPI_Count datatype and functions: MPI_Get_elements_x, MPI_Status_set_elements_x, MPI_Type_get_extent_x, MPI_Type_get_true_extent_x, and MPI_Type_size_x. This will be CMR'd to 1.7.3 if there are no objections.

Why: MPI_Count is required by the MPI 3.0 standard. This will add another checkmark by MPI 3 support.

When: Setting a short timeout of one week (Tues, July 23, 2013). Most of the changes add the new functionality but there are some changes that affect the datatype engine.

Details follow.

-Nathan

Repository @ github: https://github.com/hjelmn/ompi-count.git

Relevant commits:
General support: https://github.com/hjelmn/ompi-count/commit/db54d13404a241642fa783d5b3cc74edcb1103f2
Fortran support: https://github.com/hjelmn/ompi-count/commit/293adf84be52c2cd8acfe31be19cfe0afe14752d
Others: https://github.com/hjelmn/ompi-count/commit/6c6ca8e539da675632c249c891ff93fdbc9d8de8
        https://github.com/hjelmn/ompi-count/commit/9638ef1f245f12bb98abbf5f47e1ecfd1a018862
        https://github.com/hjelmn/ompi-count/commit/e158aa152d122e554b89498f5a71284ce1361a99

Add support for MPI_Count type and MPI_COUNT datatype and add the required
MPI-3 functions MPI_Get_elements_x, MPI_Status_set_elements_x,
MPI_Type_get_extent_x, MPI_Type_get_true_extent_x, and MPI_Type_size_x.
This commit adds only the C bindings. Fortran bindins will be added in
another commit. For now the MPI_Count type is define to have the same size
as MPI_Offset. The type is required to be at least as large as MPI_Offset
and MPI_Aint. The type was initially intended to be a ssize_t (if it was
the same size as a long long) but there were issues compiling romio with
that definition (despite the inclusion of stddef.h).

I updated the datatype engine to use size_t instead of uint32_t to support
large datatypes. This will require some review to make sure that 1) the
changes are beneficial, 2) nothing was broken by the change (I doubt
anything was), and 3) there are no performance regressions due to this
change.

George, please look over these changes and let me know if you see anything wrong with my updates to the datatype engine.

-Nathan