Add CPU pinning (taskset -c 0) and manual GC between benchmark suites

- bench-compare.mjs: detect Linux + taskset, pin benchmarks to CPU 0
- bench-compare.mjs: pass NODE_OPTIONS='--expose-gc' to vitest bench
- parser.bench.js: add beforeAll(() => globalThis.gc?.()) per suite

Co-authored-by: NullVoxPopuli <[email protected]>

Author: Copilot

scripts/bench-compare.mjs

@@ -31,6 +31,17 @@ const BASE_BRANCH = baseIdx !== -1 ? args[baseIdx + 1] : 'main';
 const iterIdx = args.indexOf('--iterations');
 const ITERATIONS = iterIdx !== -1 ? Math.max(1, parseInt(args[iterIdx + 1], 10) || 1) : 1;
 
+// ---------------------------------------------------------------------------
+// Platform detection
+// ---------------------------------------------------------------------------
+
+const IS_LINUX = process.platform === 'linux';
+const HAS_TASKSET = IS_LINUX && spawnSync('which', ['taskset'], { stdio: 'pipe' }).status === 0;
+
+if (HAS_TASKSET) {
+  console.log('📌  CPU pinning enabled (taskset -c 0) for reduced context-switch variance.');
+}
+
 // ---------------------------------------------------------------------------
 // Helpers
 // ---------------------------------------------------------------------------
@@ -49,8 +60,19 @@ function hasUncommittedChanges() {
 }
 
 function runBench(outputFile) {
-  const result = spawnSync('pnpm', ['vitest', 'bench', '--outputJson', outputFile, '--run'], {
+  const benchArgs = ['vitest', 'bench', '--outputJson', outputFile, '--run'];
+
+  // Pin to a single CPU core on Linux to eliminate cross-core migration variance.
+  const cmd = HAS_TASKSET ? 'taskset' : 'pnpm';
+  const args = HAS_TASKSET ? ['-c', '0', 'pnpm', ...benchArgs] : benchArgs;
+
+  // Expose GC so the bench file can trigger manual collections between suites.
+  const existingNodeOpts = process.env.NODE_OPTIONS || '';
+  const nodeOptions = existingNodeOpts ? `${existingNodeOpts} --expose-gc` : '--expose-gc';
+
+  const result = spawnSync(cmd, args, {
     stdio: 'inherit',
+    env: { ...process.env, NODE_OPTIONS: nodeOptions },
   });
   if (result.status !== 0) {
     console.error('\n❌  Benchmark run failed.');

tests/parser.bench.js

@@ -1,6 +1,6 @@
 import { readFileSync } from 'node:fs';
 import { fileURLToPath } from 'node:url';
-import { bench, describe } from 'vitest';
+import { bench, describe, beforeAll } from 'vitest';
 import { parseForESLint as parseGjsGts } from '../src/parser/gjs-gts-parser.js';
 import { parseForESLint as parseHbs } from '../src/parser/hbs-parser.js';
 
@@ -51,6 +51,10 @@ const BENCH_OPTIONS = {
 // ---------------------------------------------------------------------------
 
 describe('gts parser', () => {
+  beforeAll(() => {
+    globalThis.gc?.();
+  });
+
   bench(
     'small file',
     () => {
@@ -77,6 +81,10 @@ describe('gts parser', () => {
 });
 
 describe('gjs parser', () => {
+  beforeAll(() => {
+    globalThis.gc?.();
+  });
+
   bench(
     'small file',
     () => {
@@ -103,6 +111,10 @@ describe('gjs parser', () => {
 });
 
 describe('hbs parser', () => {
+  beforeAll(() => {
+    globalThis.gc?.();
+  });
+
   bench(
     'small file',
     () => {