Add a benchmark script

Makes running benchmarks a bit easier; runs with a higher scheduling
priority; and, if used with `sudo`, has an even higher scheduling
priority.

Author: sellout

development.markdown

@@ -50,7 +50,7 @@ Some tests are executables instead:
 * `stack exec transcripts -- prefix-of-filename` runs only transcript tests with a matching filename prefix.
 * `stack exec cli-integration-tests` runs the additional integration tests for cli. These tests are not triggered by `tests` or `transcripts`.
 * `stack exec unison -- transcript unison-src/transcripts-round-trip/main.md` runs the pretty-printing round trip tests
-* `stack exec unison -- transcript unison-src/transcripts-manual/benchmarks.md` runs the benchmark suite.
+* `sudo ./scripts/benchmark` runs the benchmark suite. (If you can’t or won’t run under `sudo` it will just run with lower scheduling priority)
 
 ### Building everything at once, including tests and benchmarks, but without running them:
 Do:

scripts/benchmark

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+set -euo pipefail
+SCRIPTDIR="$(dirname -- "$(readlink -f -- "${BASH_SOURCE[0]}")")"
+
+### Run the Unison benchmark suite.
+###
+### NB: If run as a superuser (e.g., under `sudo`), this will use a higher priority to hopefully get more stable
+###     results.
+
+## TODO: `transcripts` should be able to take a search path, but since it currently looks for files relative to its run
+##       path, we `cd` to where it can find them.
+cd "$SCRIPTDIR/.."
+
+niceness=0
+if [[ $EUID -eq 0 ]]; then
+    niceness=-20
+fi
+
+nice -n $niceness stack exec unison -- transcript unison-src/transcripts-manual/benchmarks.md