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Cray MPICH Integration

This document explains how AFAR modules support both Cray MPICH 8.x and 9.x, and how the correct MPI module files and pkg-config entries are selected.

For background on .pc files and pkg-config, see docs/pkgconfig.md.

MPICH Flavor Mapping

Cray MPICH versions map to different MPI module file layouts:

  • Cray MPICH 8.x -> include/mpich3.4a2
  • Cray MPICH 9.x -> include/mpich4.3.1

AFAR drops may include one or both of these directories. The modulefiles and wrappers select the best match based on CRAY_MPICH_VERSION.

mpichf90.pc Layout

The generator writes per-flavor mpichf90.pc files:

  • pkgconfig/<ver>/mpich3.4a2/mpichf90.pc
  • pkgconfig/<ver>/mpich4.3.1/mpichf90.pc

afar-amd selects the flavor at module load time based on CRAY_MPICH_VERSION and prepends the matching directory to PE_AMD_FIXED_PKGCONFIG_PATH. The wrappers re-check this at compile time to handle module swaps after afar-prgenv is loaded.

Cray MPICH Root

The mpichf90.pc file references the Cray MPICH libdir:

  • config/cray-mpich-dir.txt stores the default.
  • You can override at generation time with --cray-mpich-dir.
  • CRAY_MPICH_DIR or MPICH_DIR environment variables are also honored.

If the Cray MPICH installation moves or the PE changes, update the config and regenerate.

Validation Steps

Cray MPICH 8.x:

module load cray-mpich/8.1.31
echo "$CRAY_MPICH_VERSION"     # 8.x
echo "$AFAR_MPICH_FLAVOR"      # mpich3.4a2
pkg-config --cflags mpichf90   # includes .../include/mpich3.4a2

Cray MPICH 9.x:

module load cpe/25.09
module load cray-mpich/9.0.1
echo "$CRAY_MPICH_VERSION"     # 9.x
echo "$AFAR_MPICH_FLAVOR"      # mpich4.3.1
pkg-config --cflags mpichf90   # includes .../include/mpich4.3.1

If you swap MPICH after AFAR:

module load afar-prgenv/<ver>
module swap cray-mpich/8.1.31 cray-mpich/9.0.1
ftn -fopenmp hello.f90 -o hello

The wrapper re-syncs the flavor for the build.

Common Failure Modes

  • pkg-config --cflags mpichf90 is missing or points at the wrong include: ensure the wrappers are on PATH and PE_AMD_FIXED_PKGCONFIG_PATH is mirrored into PKG_CONFIG_PATH.
  • AFAR_MPICH_FLAVOR does not match CRAY_MPICH_VERSION: reload afar-prgenv or use the wrappers for the compile.