petsc: specify number of processors used for test case (#8015)

For Spectrum MPI, if -np is omitted, the default behavior is to
assign one process per process slot, where the default process slot
allocation is one per core. On systems with many cores, the number
of processes can exceed the size of the grid specified when the
testcase is run and the test case fails. This specifies a small
number of processes when running the test case to prevent failure.

1 files changed, 12 insertions, 0 deletions

diff --git a/var/spack/repos/builtin/packages/petsc/package.py b/var/spack/repos/builtin/packages/petsc/package.py
index ba120aac8f..6ad968bbe4 100644
--- a/var/spack/repos/builtin/packages/petsc/package.py
+++ b/var/spack/repos/builtin/packages/petsc/package.py
@@ -296,6 +296,18 @@ class Petsc(Package):
                 cc('ex50.c', '-I%s' % prefix.include, '-L%s' % prefix.lib,
                    '-lpetsc', '-lm', '-o', 'ex50')
                 run = Executable(join_path(spec['mpi'].prefix.bin, 'mpirun'))
+                # For Spectrum MPI, if -np is omitted, the default behavior is
+                # to assign one process per process slot, where the default
+                # process slot allocation is one per core. On systems with
+                # many cores, the number of processes can exceed the size of
+                # the grid specified when the testcase is run and the test case
+                # fails. Specify a small number of processes to prevent
+                # failure.
+                # For more information about Spectrum MPI invocation, see URL
+                # https://www.ibm.com/support/knowledgecenter/en/SSZTET_10.1.0/smpi02/smpi02_mpirun_options.html
+                if ('spectrum-mpi' in spec):
+                    run.add_default_arg('-np')
+                    run.add_default_arg('4')
                 run('ex50', '-da_grid_x', '4', '-da_grid_y', '4')
                 if 'superlu-dist' in spec:
                     run('ex50',