Add CPU pinning and priority for local benchmarks

- New run-bench.sh wrapper: applies taskset -c 0 (CPU pinning) and
  nice -n -20 (high priority, when running as root) for pnpm bench
- bench-compare.mjs: also uses nice -n -20 when running as root
- local-bench-summary.sh: offers to apply CPU governor and boost
  fixes interactively instead of just warning

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Author: NullVoxPopuli

package.json

@@ -25,7 +25,7 @@
     "lint:js": "eslint . --max-warnings=0",
     "lint:js:fix": "eslint . --fix --max-warnings=0",
     "lint:package": "publint",
-    "bench": "node --expose-gc tests/parser.bench.mjs",
+    "bench": "./scripts/run-bench.sh tests/parser.bench.mjs",
     "bench:compare": "node scripts/bench-compare.mjs",
     "bench:summary": "./scripts/local-bench-summary.sh",
     "test": "vitest run"

scripts/bench-compare.mjs

@@ -105,19 +105,30 @@ try {
     CONTROL_DIR,
   ];
 
-  // CPU pinning on Linux to reduce cross-core migration variance
+  // CPU pinning + high priority on Linux for lower variance
   const IS_LINUX = process.platform === 'linux';
   const HAS_TASKSET = IS_LINUX && spawnSync('which', ['taskset'], { stdio: 'pipe' }).status === 0;
+  const HAS_NICE = IS_LINUX && spawnSync('which', ['nice'], { stdio: 'pipe' }).status === 0;
 
   let cmd = 'node';
   let fullArgs = benchArgs;
 
   if (HAS_TASKSET) {
     cmd = 'taskset';
     fullArgs = ['-c', '0', 'node', ...benchArgs];
-    console.error('📌  CPU pinning enabled (taskset -c 0)\n');
+    console.error('📌  CPU pinning enabled (taskset -c 0)');
   }
 
+  if (HAS_NICE && process.getuid?.() === 0) {
+    fullArgs = ['-n', '-20', cmd, ...fullArgs];
+    cmd = 'nice';
+    console.error('⚡  High priority enabled (nice -n -20)');
+  } else if (HAS_NICE) {
+    console.error('💡  Run with sudo for high scheduling priority (nice -n -20)');
+  }
+
+  console.error('');
+
   const result = spawnSync(cmd, fullArgs, {
     stdio: 'inherit',
     cwd: ROOT,

scripts/local-bench-summary.sh

@@ -2,28 +2,54 @@
 
 # Check CPU tuning on Linux — poor settings cause massive variance
 hw_warnings=""
+hw_fixes=()
 
 if [ -f /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor ]; then
   gov=$(cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor)
   if [ "$gov" != "performance" ]; then
     hw_warnings+="⚠️  CPU governor is '$gov' — benchmark results will be noisy.
-   Fix with: sudo cpupower frequency-set -g performance
 "
+    hw_fixes+=("sudo cpupower frequency-set -g performance")
   fi
 fi
 
 if [ -f /sys/devices/system/cpu/cpufreq/boost ]; then
   boost=$(cat /sys/devices/system/cpu/cpufreq/boost)
   if [ "$boost" = "1" ]; then
     hw_warnings+="⚠️  CPU boost is enabled — frequency varies with thermals.
-   Fix with: echo 0 | sudo tee /sys/devices/system/cpu/cpufreq/boost
 "
+    hw_fixes+=("echo 0 | sudo tee /sys/devices/system/cpu/cpufreq/boost")
+  fi
+elif [ -f /sys/devices/system/cpu/intel_pstate/no_turbo ]; then
+  no_turbo=$(cat /sys/devices/system/cpu/intel_pstate/no_turbo)
+  if [ "$no_turbo" = "0" ]; then
+    hw_warnings+="⚠️  Intel Turbo Boost is enabled — frequency varies with thermals.
+"
+    hw_fixes+=("echo 1 | sudo tee /sys/devices/system/cpu/intel_pstate/no_turbo")
   fi
 fi
 
 if [ -n "$hw_warnings" ]; then
   echo ""
   echo "$hw_warnings"
+
+  if [ ${#hw_fixes[@]} -gt 0 ] && [ -t 0 ]; then
+    echo "Fix with:"
+    for fix in "${hw_fixes[@]}"; do
+      echo "  $fix"
+    done
+    echo ""
+    read -rp "Apply these fixes now? [y/N] " answer
+    if [[ "$answer" =~ ^[Yy]$ ]]; then
+      for fix in "${hw_fixes[@]}"; do
+        echo "→ $fix"
+        eval "$fix"
+      done
+      echo ""
+      echo "✅  CPU tuning applied."
+      echo ""
+    fi
+  fi
 fi
 
 export BENCH_JSON_OUTPUT=./bench-results.json

scripts/run-bench.sh

@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+#
+# Wrapper that runs a node command with CPU pinning and high priority
+# when available, for lower-variance benchmarks.
+#
+# Usage: ./scripts/run-bench.sh <node args...>
+
+set -euo pipefail
+
+NODE_ARGS=("--expose-gc" "$@")
+
+CMD=(node "${NODE_ARGS[@]}")
+
+# CPU pinning on Linux — keep the process on a single core
+if command -v taskset &>/dev/null; then
+  CMD=(taskset -c 0 "${CMD[@]}")
+  echo "📌  CPU pinning enabled (taskset -c 0)" >&2
+fi
+
+# High scheduling priority (best-effort, needs root for negative values)
+if command -v nice &>/dev/null; then
+  if [ "$(id -u)" = "0" ]; then
+    CMD=(nice -n -20 "${CMD[@]}")
+    echo "⚡  High priority enabled (nice -n -20)" >&2
+  else
+    echo "💡  Run with sudo for high scheduling priority (nice -n -20)" >&2
+  fi
+fi
+
+echo "" >&2
+exec "${CMD[@]}"