Switch from Open MPI to MPICH (Open MPI 5.x requires PMIx)

Author: Sébastien Loisel

.github/workflows/CI.yml

@@ -101,14 +101,14 @@ jobs:
         env:
           GH_TOKEN: ${{ github.token }}
 
-      - name: Configure MPI to use bundled Open MPI
+      - name: Configure MPI to use bundled MPICH
         run: |
           # Write LocalPreferences.toml directly to configure MPI.jl
           # This will be picked up by julia-buildpkg
           cat > LocalPreferences.toml << 'EOF'
           [MPIPreferences]
           _format = "1.0"
-          abi = "OpenMPI"
+          abi = "MPICH"
           binary = "system"
           libmpi = "/tmp/petsc_strumpack/lib/libmpi.so"
           mpiexec = "/tmp/petsc_strumpack/bin/mpiexec"
@@ -138,11 +138,6 @@ jobs:
           JULIA_PETSC_LIBRARY: /tmp/petsc_strumpack/lib/libpetsc.so
           LD_LIBRARY_PATH: /tmp/petsc_strumpack/lib
           MPIEXEC_PATH: /tmp/petsc_strumpack/bin/mpiexec
-          OPAL_PREFIX: /tmp/petsc_strumpack
-          # Open MPI 5.x MCA parameters for CI environment
-          OMPI_MCA_plm: fork
-          OMPI_MCA_btl: tcp,self
-          PRTE_MCA_plm: fork
         run: |
           # Run tests directly instead of Pkg.test() to preserve LocalPreferences.toml
           # (Pkg.test() creates a fresh temp environment that loses MPI preferences)

.github/workflows/build-petsc-strumpack.yml

@@ -103,14 +103,14 @@ jobs:
           tag_name: ${{ steps.build-info.outputs.tag }}
           name: PETSc ${{ steps.build-info.outputs.petsc_version }} with STRUMPACK${{ inputs.with_cuda && ' + CUDA' || '' }}
           body: |
-            Pre-built PETSc library with STRUMPACK solver and bundled Open MPI.
+            Pre-built PETSc library with STRUMPACK solver and bundled MPICH.
 
             **Build Configuration:**
             - PETSc version: ${{ steps.build-info.outputs.petsc_version }}
             - STRUMPACK: enabled
             - CUDA: ${{ inputs.with_cuda && 'enabled' || 'disabled' }}
             - Platform: Linux x86_64 (Ubuntu)
-            - MPI: Bundled Open MPI (self-contained, no system MPI required)
+            - MPI: Bundled MPICH (self-contained, no system MPI required)
 
             **Usage:**
             ```bash

src/build_petsc.jl

@@ -307,16 +307,17 @@ end
 function _build_petsc_with_strumpack(src_dir::String, install_dir::String, with_debugging::Bool,
                                      with_cuda::Bool, verbose::Bool)
     # Build configuration flags - includes both STRUMPACK and MUMPS
-    # Bundle Open MPI with PETSc for ABI compatibility (avoids mismatch between build/test environments)
+    # Bundle MPICH with PETSc for ABI compatibility (avoids mismatch between build/test environments)
+    # Note: We use MPICH instead of Open MPI because Open MPI 5.x requires PMIx server setup
     configure_flags = [
         "--prefix=$install_dir",
-        "--download-openmpi",   # Bundle Open MPI for guaranteed ABI compatibility
+        "--download-mpich",   # Bundle MPICH for guaranteed ABI compatibility
         "--with-fc=gfortran",   # Fortran needed for fblaslapack
         "--with-debugging=$(with_debugging ? 1 : 0)",
         "--with-shared-libraries=1",
     ]
     if verbose
-        @info "Building with bundled Open MPI (for ABI compatibility)"
+        @info "Building with bundled MPICH (for ABI compatibility)"
     end
 
     # Add common dependencies