test: add simple MPI scaling script to src/test/scaling

Problem: A reusable script to drive MPI scaling tests has been written
but is not available so it can be conveniently reused.

Add src/test/scaling/mpi-scale.sh - a script that uses the timing
mode of t/mpi/hello to generate a table of MPI init/barrier/finalize
timing results as the number of tasks scale up.

Author: grondo

src/test/scaling/mpi-scale.sh

@@ -0,0 +1,44 @@
+#!/bin/bash
+##############################################################
+# Copyright 2024 Lawrence Livermore National Security, LLC
+# (c.f. AUTHORS, NOTICE.LLNS, COPYING)
+#
+# This file is part of the Flux resource manager framework.
+# For details, see https://github.com/flux-framework.
+#
+# SPDX-License-Identifier: LGPL-3.0
+##############################################################
+
+NNODES=$(flux resource list -no {nnodes})
+NCORES=$(flux resource list -no {ncores})
+CPN=$((${NCORES}/${NNODES}))
+
+printf "MPI scale testing on ${LCSCHEDCLUSTER:-$(hostname)}\n"
+printf "TIME: $(date -Is)\n"
+printf "INFO: $(flux resource info)\n"
+printf "TOPO: $(flux getattr tbon.topo)\n"
+printf "\n"
+printf "%6s %8s %14s %14s %14s %14s\n" NODES NTASKS INIT BARRIER FINALIZE TOTAL
+
+seq2()
+{
+    local start=$1
+    local end=$2
+    local printend=1
+
+    while [[ $start -lt $end ]]; do
+        printf "$start\n"
+        [[ $start = $end ]] && printend=0
+        ((start*=2))
+    done
+    [[ $printend = 1 ]] && printf "$end\n"
+}
+
+flux bulksubmit --watch --progress --quiet --nodes={0} --tasks-per-node={1} \
+    --exclusive \
+    --env=FLUX_MPI_TEST_TIMING=t \
+    ./t/mpi/hello \
+    ::: $(seq2 1 ${NNODES}) \
+    ::: $(seq2 1 ${CPN})
+
+# vi: ts=4 sw=4 expandtab