benchmarks: add release comparison script

this script is one part of the release procedure, according to:

  https://www.cp2k.org/dev:release_checklist?rev=1528810849

benchmarks/QS/check-release-comparison.py

@@ -0,0 +1,150 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+"""
+Run the benchmark in this directory with multiple combinations of OpenMP threads and MPI ranks,
+calculate the average of the final total energies, the variance and checks that each energy is
+within 1e-10 of the average.
+"""
+
+import subprocess
+import re
+import pathlib
+import argparse
+import tempfile
+import os
+import sys
+
+SCRIPT_DIR = pathlib.Path(__file__).parent
+
+TEST_COMBINATIONS = [
+    # OMP_NUM_THREADS, MPI_RANKS
+    (0, 8),  # 0 switches to using [ps]opt
+    (1, 8),
+    (2, 4),
+    (4, 2),
+    (8, 1),
+    (8, 0),  # 0 switches to using s[smp,opt]
+]
+
+
+def cp2k_version(omp_num_threads, mpi_ranks):
+    """Generates the correct CP2K version string based on number of threads and ranks"""
+    return f"{'p' if mpi_ranks > 0 else 's'}{'smp' if omp_num_threads > 0 else 'opt'}"
+
+
+def ofname(omp_num_threads, mpi_ranks, input_file, version):
+    """Returns a string of the form 'H2O-32-sopt-1-8.out' with additional steps"""
+    return (
+        f"{input_file.stem}-{version}-{max(1,mpi_ranks)}-{max(1,omp_num_threads)}.out"
+    )
+
+
+TOTAL_FORCE_EVAL_RE = re.compile(
+    r"^\s*ENERGY\| Total FORCE_EVAL.+?:\s*(?P<energy>.+)\n", re.MULTILINE
+)
+
+
+def run_benchmark(cp2k_exe_dir, input_file, mpi_wrapper="mpiexec -np {mpi_ranks}"):
+    energies = []
+
+    for omp_num_threads, mpi_ranks in TEST_COMBINATIONS:
+        env = {**os.environ, "OMP_NUM_THREADS": "1"}  # override OMP_NUM_THREADS
+        args = []
+
+        if mpi_ranks > 0:
+            args = mpi_wrapper.format(mpi_ranks=mpi_ranks).split()
+
+        if omp_num_threads > 0:
+            env["OMP_NUM_THREADS"] = str(omp_num_threads)
+
+        version = cp2k_version(omp_num_threads, mpi_ranks)
+        outfile = SCRIPT_DIR / ofname(omp_num_threads, mpi_ranks, input_file, version)
+
+        args += [cp2k_exe_dir / f"cp2k.{version}", input_file]
+        with tempfile.TemporaryDirectory(
+            prefix="release-comparison."
+        ) as tmpdir, outfile.open("w+", encoding="utf-8") as fhandle:
+            print(
+                f"Running benchmark '{input_file.name}' with {args[-2]} using {mpi_ranks} MPI ranks and {omp_num_threads} OpenMP threads"
+            )
+            subprocess.run(
+                args,
+                stdout=fhandle,
+                stderr=subprocess.STDOUT,
+                check=True,
+                encoding="utf-8",
+                cwd=tmpdir,
+                env=env,
+            )
+
+            fhandle.seek(0)  # be kind, rewind
+            for match in TOTAL_FORCE_EVAL_RE.finditer(fhandle.read()):
+                pass  # get the last match (it's an MD, we have multiple total energies)
+            energies += [float(match["energy"])]
+            print(f".. run was successful, final total energy: {energies[-1]:20.14f}")
+
+    mean = sum(energies) / len(energies)
+    if len(energies) > 1:
+        var = sum((e - mean) ** 2 for e in energies) / len(energies)
+    else:
+        var = float("NaN")
+
+    allok = True
+
+    print(
+        """
+CP2K | # Threads | # Ranks | Energy
+-----+-----------+---------+------------------------"""
+    )
+
+    for (omp_num_threads, mpi_ranks), energy in zip(TEST_COMBINATIONS, energies):
+        version = cp2k_version(omp_num_threads, mpi_ranks)
+        mark = "✔"
+        if abs(energy - mean) >= 1e-10:
+            mark = "!"
+            allok = False
+
+        print(
+            f"{version} | {omp_num_threads:9d} | {mpi_ranks:7d} | {energy:20.14f} {mark}"
+        )
+
+    print(
+        f"""\
+----------------------------------------------------
+mean: {mean:20.14f} +/- {var:16.12e}"""
+    )
+
+    return allok
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser(
+        description=__doc__, formatter_class=argparse.ArgumentDefaultsHelpFormatter
+    )
+    parser.add_argument(
+        "--cp2k-exe-dir",
+        metavar="<CP2K-exe-directory>",
+        type=pathlib.Path,
+        help="Path to where cp2k.* can be found",
+        default=(SCRIPT_DIR / "../../../exe/Linux-x86-64-gfortran"),
+    )
+    parser.add_argument(
+        "--input",
+        metavar="<CP2K-input to use>",
+        type=pathlib.Path,
+        help="Path to a CP2K input file to run the benchmark for",
+        default=(SCRIPT_DIR / "H2O-32.inp"),
+    )
+    args = parser.parse_args()
+
+    # resolve any relative path absolute in respect to the current working directory
+    cp2k_exe_dir = (pathlib.Path.cwd() / args.cp2k_exe_dir).resolve()
+    input_file = (pathlib.Path.cwd() / args.input).resolve()
+
+    if not cp2k_exe_dir.exists():
+        print(f"ERROR: '{cp2k_exe_dir}' could not be found")
+        sys.exit(1)
+
+    if not run_benchmark(cp2k_exe_dir, input_file):
+        sys.exit(1)