Simplified version

CMakeLists.txt

@@ -131,18 +131,11 @@ adios_option(SysVShMem "Enable support for SysV Shared Memory IPC on *NIX" AUTO)
 include(${PROJECT_SOURCE_DIR}/cmake/DetectOptions.cmake)
 
 if(ADIOS2_HAVE_MPI)
-  cmake_host_system_information(RESULT ncores QUERY NUMBER_OF_PHYSICAL_CORES)
-  message("-- Found MPI nprocs = " ${ncores})
-  if(ncores LESS 4)
-    if (NOT "$ENV{OMPI_MCA_rmaps_base_oversubscribe}" STREQUAL "yes")
-      message("-- Reducing MPI nprocs to " ${ncores} " for tests")
-      set(MPIEXEC_MAX_NUMPROCS ${ncores})
-    else()
-      message("-- Found OMPI_MCA_rmaps_base_oversubscribe")
-      set(MPIEXEC_MAX_NUMPROCS 4)
-      message("-- Setting MPI nprocs = " ${MPIEXEC_MAX_NUMPROCS})
-    endif()
+  if(MPIEXEC_MAX_NUMPROCS LESS 4 AND "$ENV{OMPI_MCA_rmaps_base_oversubscribe}")
+    message(STATUS "OpenMPI oversubscribe detected: raising MPIEXEC_MAX_NUMPROCS to 4 for testing")
+    set(MPIEXEC_MAX_NUMPROCS 4 CACHE STRING "" FORCE)
   endif()
+
   # Workaround for MPI forcing the link of C++ bindings
   add_definitions(-DOMPI_SKIP_MPICXX -DMPICH_SKIP_MPICXX)
 endif()