WebAssembly (WASM) for High Performance Apps · レッスン

WASMのパフォーマンスベンチマーク

パフォーマンスベンチマークを設定・実行し、WebAssemblyコードの速度と効率を測定します

「WASMのパフォーマンスベンチマーク」はCoddyKit上の無料WebAssembly (WASM) for High Performance Appsレッスンです。これはレッスン1/4です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはWebAssembly (WASM) for High Performance Apps学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 WebAssembly (WASM) for High Performance Appsコースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

Why Measure WASM Performance?

When building high-performance web applications, understanding how different parts of your code perform is crucial. WebAssembly (WASM) is designed for speed, but how do we confirm it's delivering?

Benchmarking is the process of running tests to measure and compare the performance of code. It helps us:

Verify performance claims.
Identify bottlenecks.
Compare different implementations (e.g., WASM vs. JavaScript).

Key Performance Metrics

When benchmarking WASM, we often look at several metrics:

Execution Time: How long a WASM function takes to run. This is usually the primary focus.
Load Time: How long it takes for the WASM module to be fetched, compiled, and instantiated.
Memory Usage: How much memory the WASM module consumes.
Startup Time: The time from module instantiation to the first meaningful operation.

For this lesson, we'll focus mostly on execution time.

Measuring Time in JavaScript

Since WASM modules are loaded and called from JavaScript in the browser, we'll use JavaScript's built-in APIs to measure performance.

The Date.now() method can give you a rough idea, but it's not precise enough for micro-benchmarking.

A better option is performance.now(), which provides high-resolution timestamps, accurate to microseconds.

Using `performance.now()`

The performance.now() method returns a DOMHighResTimeStamp, representing the number of milliseconds since the page started loading, with sub-millisecond precision.

To measure the duration of an operation, you record the time before and after the operation, then subtract the start time from the end time.

const startTime = performance.now();
// Your code here
const endTime = performance.now();
const duration = endTime - startTime;

This duration will be in milliseconds.

Benchmarking a WASM Function

Let's see how to measure the execution time of a hypothetical WASM function. We'll simulate a WASM function for this example.

Remember, for accurate results, you'd load a real WASM module and call its exported functions.

    // Simulate a WASM function for demonstration
    function addNumbersWasm(a, b) {
      // In a real scenario, this would be a call to an
      // exported WASM function, e.g., wasmModule.instance.exports.add(a, b)
      let sum = 0;
      for (let i = 0; i < 1000000; i++) {
        sum += (a + b); // Simulate some work
      }
      return sum;
    }

    // --- Benchmarking setup ---
    const num1 = 10;
    const num2 = 20;

    console.log("Starting WASM benchmark...");

    const startTime = performance.now();
    const result = addNumbersWasm(num1, num2);
    const endTime = performance.now();

    const durationMs = endTime - startTime;

    console.log("Result:", result);
    console.log(`WASM function took: ${durationMs.toFixed(3)} ms`);

Multiple Runs for Accuracy

A single measurement is rarely enough. Browser environments are complex, with many background processes that can affect timing.

To get reliable results, you should run your benchmarked code many times (e.g., thousands or millions of iterations) and calculate the average execution time.

This helps smooth out transient performance spikes and gives a more representative picture.

Warm-up and JIT Compilation

Modern JavaScript engines use Just-In-Time (JIT) compilers. When code runs for the first time, it might be executed by an interpreter. After a few runs, the JIT compiler optimizes it, making subsequent runs much faster.

This means your first few benchmark runs might be slower than steady-state performance.

To account for this, perform "warm-up" runs before starting your actual measurements. Discard the results from these initial runs.

WASM vs. JavaScript Comparison

One common use of benchmarking is to compare the performance of a WASM implementation against its equivalent JavaScript version.

You would write the same logic in both WASM (e.g., in C/C++/Rust compiled to WASM) and plain JavaScript, then benchmark both separately under similar conditions.

// Benchmark WASM version
const wasmDuration = measureWasmFunction();

// Benchmark JS version
const jsDuration = measureJsFunction();

console.log(`WASM: ${wasmDuration} ms, JS: ${jsDuration} ms`);

This comparison helps justify the overhead of using WASM for specific tasks.

Benchmarking Best Practices

For robust benchmarking:

Isolate: Measure only the code you're interested in. Avoid measuring UI updates or network requests.
Consistent Environment: Run tests on the same hardware, browser, and OS. Close other applications.
Disable Optimizations: For initial debugging, some browser dev tools might have options to disable JIT to see raw performance.
Statistical Analysis: Beyond averages, consider median, standard deviation, and outliers.
Use Libraries: For complex scenarios, consider libraries like benchmark.js which handle warm-ups, multiple runs, and statistical analysis automatically.

Benchmarking Principles

Which of the following are good practices when benchmarking WebAssembly code in a browser environment?

Recap: Benchmarking WASM

We've learned how to approach benchmarking WebAssembly performance.

Benchmarking helps verify performance and identify bottlenecks.
performance.now() is key for precise time measurements in JavaScript.
Running multiple iterations and including warm-up runs are crucial for accurate results.
Comparing WASM to JavaScript helps understand its real-world benefits.

Next, we'll dive into specific optimization strategies to make your Rust-compiled WASM even faster!

よくある質問

「WASMのパフォーマンスベンチマーク」レッスンは無料ですか？

はい。「WASMのパフォーマンスベンチマーク」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、WebAssembly (WASM) for High Performance Appsコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 WebAssembly (WASM) for High Performance Appsコースには全4レッスンが含まれています。

「WASMのパフォーマンスベンチマーク」で何を学びますか？

パフォーマンスベンチマークを設定・実行し、WebAssemblyコードの速度と効率を測定しますブラウザで直接実行するハンズオンコードでWebAssembly (WASM) for High Performance Appsを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

WebAssembly (WASM) for High Performance Appsを始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのWebAssembly (WASM) for High Performance Appsは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン1/4です。

「WASMのパフォーマンスベンチマーク」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このWebAssembly (WASM) for High Performance Appsレッスンでコードを書いて実行できますか？

はい。すべてのWebAssembly (WASM) for High Performance Appsレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

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