lib: default node:bench warmup to 10 invocations

Signed-off-by: RafaelGSS <rafael.nunu@hotmail.com>

Author: RafaelGSS

doc/api/bench.md

@@ -74,6 +74,12 @@ once to provide an externally measured sample. Setup before `start()` and
 cleanup after `end()` are outside the measured region. Promise-returning
 functions are awaited.
 
+By default, ten unreported warmup invocations run before the measured samples
+so that early samples are less likely to be taken before the measured code has
+been optimized. A fixed warmup count does not guarantee a stable optimization
+state; inspect raw `samples` and increase `warmup` when early samples are
+consistently slower. Set `warmup` to `0` to measure from the first invocation.
+
 By default, an event loop turn occurs between sample invocations. An embedded
 runner can disable this using `yieldBetweenSamples`. The runner executes
 benchmarks serially, but it does not provide process isolation. Other work in
@@ -336,7 +342,7 @@ added: v26.9.0
   * `timeout` {number} The number of milliseconds after which the benchmark
     fails. **Default:** `Infinity`.
   * `warmup` {number} The number of unreported callback invocations before
-    measured samples. Must be a 32-bit unsigned integer. **Default:** `0`.
+    measured samples. Must be a 32-bit unsigned integer. **Default:** `10`.
 * `fn` {Function|AsyncFunction} The benchmark function. It receives a
   {BenchContext}.
 * Returns: {Promise} Fulfilled with the benchmark result after a top-level

doc/api/cli.md

@@ -630,6 +630,8 @@ added: v26.9.0
 
 Overrides the number of unreported warmup callback invocations for every
 selected benchmark. `count` must be an integer between `0` and `4294967295`.
+Without this option, each benchmark uses its own `warmup` value, which defaults
+to `10`.
 
 ### `--build-sea=config`
 

doc/node.1

@@ -384,6 +384,8 @@ selected benchmark. A benchmark may finish earlier by calling
 .It Fl -bench-warmup Ns = Ns Ar count
 Overrides the number of unreported warmup callback invocations for every
 selected benchmark. \fBcount\fR must be an integer between \fB0\fR and \fB4294967295\fR.
+Without this option, each benchmark uses its own \fBwarmup\fR value, which defaults
+to \fB10\fR.
 .
 .It Fl -build-sea Ns = Ns Ar config
 Generates a single executable application from a JSON

lib/internal/bench_runner/benchmark.js

@@ -47,7 +47,7 @@ const { structuredClone } = require('internal/worker/js_transferable');
 
 const { bigint: hrtime } = process.hrtime;
 const kDefaultSamples = 30;
-const kDefaultWarmup = 0;
+const kDefaultWarmup = 10;
 const kEmptyDiagnosticChannels = ObjectFreeze([]);
 const kEmptyNamePath = ObjectFreeze([]);
 const kEmptyParams = ObjectFreeze({ __proto__: null });

test/fixtures/bench-runner/diagnostic.cjs

@@ -9,6 +9,7 @@ const diagnosticChannel = channel(channelName);
 bench('diagnostic relay', {
   diagnosticChannels: [channelName],
   samples: 1,
+  warmup: 0,
 }, (b) => {
   const message = { value: 42n };
   diagnosticChannel.publish(message);

test/fixtures/bench-runner/many-records.cjs

@@ -2,7 +2,7 @@
 
 const { bench } = require('node:bench');
 
-bench('many records', { samples: 30 }, (b) => {
+bench('many records', { samples: 30, warmup: 0 }, (b) => {
   process.stdout.write(`${b.index}\n`);
   b.record({ duration_ns: 1n, operations: 1 });
 });

test/fixtures/bench-runner/recorded-detail.cjs

@@ -2,7 +2,7 @@
 
 const { bench } = require('node:bench');
 
-bench('recorded detail', { samples: 3 }, (b) => {
+bench('recorded detail', { samples: 3, warmup: 0 }, (b) => {
   b.record({
     __proto__: null,
     detail: {

test/fixtures/bench-runner/serial.js

@@ -9,7 +9,7 @@ module.exports = function register(name) {
   fs.writeFileSync(lock, `${process.pid}`, { flag: 'wx' });
   process.on('exit', () => fs.unlinkSync(lock));
 
-  bench(name, { samples: 1 }, async (b) => {
+  bench(name, { samples: 1, warmup: 0 }, async (b) => {
     b.start();
     await setTimeout(25);
     b.end(1);

test/fixtures/bench-runner/utf8-output.cjs

@@ -6,7 +6,7 @@ const { bench } = require('node:bench');
 const output = Buffer.from('split:\u20ac\n');
 process.stdout.write(output.subarray(0, 7));
 
-bench('UTF-8 output', { samples: 1 }, async (b) => {
+bench('UTF-8 output', { samples: 1, warmup: 0 }, async (b) => {
   b.start();
   await setTimeout(20);
   process.stdout.write(output.subarray(7));

test/parallel/test-bench-auto-run.js

@@ -14,7 +14,9 @@ const child = spawnSync(process.execPath, [
 ]);
 assert.strictEqual(child.status, 1);
 
-const completion = bench('automatic execution', common.mustCall((b) => {
+const completion = bench('automatic execution', {
+  warmup: 0,
+}, common.mustCall((b) => {
   b.record({ duration_ns: 1n, operations: 1 });
 }, 30));