iso-bench

iso-bench is a small benchmark library focused on avoiding optimization/deoptimization pollution between tests by isolating them.

Motivation

I've always used benchmark.js for my benchmark tests, but I noticed that changing the tests order also changed the performance outcome. They were getting polluted between them with V8 and memory optimizations/deoptimizations. After this, I decided to take advantage of forking to do tests in completely separated processes with their own V8 instances, memory and so on, to avoid present and future optimization/deoptimization pollution.

All single threaded benchmark libraries, like benny or benchmark.js have this problem, so you may had this pollution on your tests and you didn't even notice, just thinking that one test was faster than the other. This happened to me, and when I noticed the problem I had to redo some PacoPack code ☹️.

Pollution examples

Running this test on benchmark.js, it will return different outcomes. Note how I rerun the very same first test again:

const Benchmark = require("benchmark");
const functions = {
    method: function(buf:Buffer) {
        return buf.readUint8(0);
    },
    direct: function(buf:Buffer) {
        return buf[0];
    },
    method_again: function(buf:Buffer) {
        return buf.readUint8(0);
    }
};
const buffers = new Array(1000).fill(0).map(() => {
    const buf = Buffer.allocUnsafe(1);
    buf[0] = Math.floor(Math.random() * 0xFF);
    return buf;
});
const suite = new Benchmark.Suite();
for (const [type, fn] of Object.entries(functions)) {
    suite.add(`${type}`, () => {
        for (let i = 0; i < buffers.length; i++) {
            fn(buffers[i]);
        }
    });
}
suite.on("cycle", event => {
    console.log(String(event.target));
}).run({
    async: true
});

Which yields the next results:

method       x 314,830 ops/sec
direct       x 300,522 ops/sec
method_again x 187,985 ops/sec // WTF. SLOWER THAN ITS "method" CLONE??

And if I run the direct test first, it is even worse:

direct       x 1,601,246 ops/sec // WTF. 5 TIMES FASTER THAN BEFORE??
method       x 183,015 ops/sec // This test already got deoptimized
method_again x 183,956 ops/sec

On iso-bench this is not possible, as every test will run in a completely different process. No matter the order, the outcome will be equally stable. This is the very same test on iso-bench:

import { IsoBench } from "..";
const bench = new IsoBench();
const functions = {
  method: function(buf:Buffer) {
      return buf.readUint8(0);
  },
  direct: function(buf:Buffer) {
      return buf[0];
  },
  method_again: function(buf:Buffer) {
      return buf.readUint8(0);
  }
};
const buffers = new Array(1000).fill(0).map(() => {
  const buf = Buffer.allocUnsafe(1);
  buf[0] = Math.floor(Math.random() * 0xFF);
  return buf;
});
for (const [type, fn] of Object.entries(functions)) {
  bench.add(`${type}`, () => {
      for (let i = 0; i < buffers.length; i++) {
          fn(buffers[i]);
      }
  });
}
bench.run();

Which yields these results with zero pollution:

method       - 753.719 op/s. 10 samples in 1042 ms. 1.021x 
direct       - 1.531.781 op/s. 10 samples in 1022 ms. 2.075x (BEST)
method_again - 738.039 op/s. 10 samples in 1018 ms. 1.000x (WORSE)

Installation

npm install iso-bench

Usage

Example code:

import { IsoBench } from "iso-bench";

const bench = new IsoBench("My bench");
bench.add("indexOf", () => {
    "thisisastring".indexOf("a") > -1;
})
.add("RegExp", () => {
    /a/.test("thisisastring");
})
.run();

Documentation

new IsoBench(name, options?);

Creates a new IsoBench to add tests.

name: The name of this IsoBench instance. Optional.
options: Object:
- parallel: The amount of parallel tests to run. Although a test may end before its predecessor, the log output will honor the test order. Defaults to 1.
- ms: The minimum time to invest on each test. The library will automatically increase the amount of cycles to reach a minimum of minMs between tests to take samples. Defaults to 1000.
- minMs: The minimum time to invest on each cycle loop, so the sample is taken into account to calculate the performance. Defaults to 100.

bench.add(name, test);

Adds new test.

name: The name of this test.
test: The test function to run.

bench.run();

Runs the tests and shows the output in the console. Returns a Promise that will resolve when all the tests are completed.

mindplay-dk / iso-bench