chore: Integrate benchmark output in GHA

The code comes from @ivanvc in etcd-io/bbolt#750

.github/workflows/ci.yml

@@ -164,7 +164,17 @@ jobs:
 
     - name: Benchmark tests
       run: |
-        make test-benchmark-compare
+        BENCHSTAT_OUTPUT_FILE=result.txt make test-benchmark-compare
+    - run: |
+        echo "\`\`\`" >> "$GITHUB_STEP_SUMMARY"
+        cat result.txt >> "$GITHUB_STEP_SUMMARY"
+        echo "\`\`\`" >> "$GITHUB_STEP_SUMMARY"
+        cat <<EOL >> "$GITHUB_STEP_SUMMARY"
+        <hr />
+        The table shows the median and 90% confidence interval (CI) summaries for each benchmark comparing the HEAD and the BASE, and an A/B comparison under "vs base". The last column shows the statistical p-value with ten runs (n=10).
+        The last row has the Geometric Mean (geomean) for the given rows in the table.
+        Refer to [benchstat's documentation](https://pkg.go.dev/golang.org/x/perf/cmd/benchstat) for more help.
+        EOL
 
   ci-build-kube-state-metrics:
     name: ci-build-kube-state-metrics

tests/compare_benchmarks.sh

@@ -9,7 +9,7 @@ set -u
 [[ "$#" -le 2 ]] || echo "At least one argument required, $# provided."
 
 REF_CURRENT="$(git rev-parse --abbrev-ref HEAD)"
-REF_TO_COMPARE=$1
+REF_TO_COMPARE="${1}"
 
 COUNT=${2:-"1"}
 
@@ -42,4 +42,8 @@ echo ""
 echo "### Result"
 echo "old=${REF_TO_COMPARE} new=${REF_CURRENT}"
 
-benchstat "${RESULT_TO_COMPARE}" "${RESULT_CURRENT}"
+if [[ -z "${BENCHSTAT_OUTPUT_FILE}" ]]; then
+	benchstat BASE="${RESULT_TO_COMPARE}" HEAD="${RESULT_CURRENT}" | tee "${BENCHSTAT_OUTPUT_FILE}"
+else
+	benchstat BASE="${RESULT_TO_COMPARE}" HEAD="${RESULT_CURRENT}"
+fi