Chuyển tới nội dung chính

Profiling and Benchmarking

Blindly guessing what is slowing down your app is dangerous. You must measure objectively.

Android Studio Profiler​

The central built-in suite for debugging performance.

1. CPU Profiler​

  • Tracks method execution. If your app stutters when scrolling, record a trace.
  • Flame Charts: Show the exact hierarchy of method calls and width represents time consumed by that method.
  • Use this to identify JSON parsing running heavily on the Main thread.

2. Memory Profiler​

  • Tracks memory allocations over time.
  • Allows capturing a Heap Dump.
  • Captures Allocation Tracking (identifies code loops that allocate hundreds of temporary String objects repetitively—GC Churn).

3. Network Profiler​

  • Validates that image loading libraries are actually caching (ensure subsequent identical requests don't show network spikes).

UI Jank and Frames​

A device screen refreshes continuously (60Hz = 16.6ms per frame; 120Hz = 8.3ms per frame). If your Main thread takes 30ms to parse data or layout a complex View, the screen skips rendering a frame. This is Jank.

Detecting Jank​

  • StrictMode: Enable StrictMode in debug builds. It intentionally crashes or flashes the screen if you accidentally do Network or Disk I/O on the Main thread.
  • Systrace / Perfetto: Highly advanced system-wide profiling tools tracing exactly how your app interacts with OS surface flinger hardware layers.

Jetpack Macrobenchmark​

Allows you to write JUnit-style tests that evaluate app performance (Startup, Scrolling Jank) preferably on physical devices for representative results (emulators can be used for development checks).

@RunWith(AndroidJUnit4::class)
class StartupBenchmark {
    @get:Rule
    val benchmarkRule = MacrobenchmarkRule()

    @Test
    fun startup() = benchmarkRule.measureRepeated(
        packageName = "com.myapp.pkg",
        metrics = listOf(StartupTimingMetric()),
        iterations = 5,
        startupMode = StartupMode.COLD
    ) {
        pressHome()
        startActivityAndWait()
    }
}

Compose Recomposition Performance​

Use Layout Inspector and compiler reports to form a hypothesis, then inspect frame timing/traces. Recomposition count alone does not prove jank. With strong skipping, unstable parameters do not automatically prevent skipping. @Stable/@Immutable are correctness contracts, not fixes to apply blindly. See Compose stability.

Interview Questions​

Q: What is StrictMode and how do you use it? Answer: StrictMode is a developer tool that detects things you might be doing by accident on the main thread (Disk Reads/Writes, Network operations, slow SQLite access) and brings them to your attention via Logcat, crashing the app, or flashing a red rectangle on the screen. It is initiated inside Application.onCreate.

Q: In Profiling, what is the difference between Wall Clock time and Thread time? Answer: Thread Time is the exact CPU time the thread actively spent executing that specific method. Wall Clock time is the real-world time that passed between the method starting and finishing. If Wall Clock is 10 seconds, but Thread Time is 0.5s, it indicates that your thread was parked or suspended (perhaps waiting on an I/O read or Coroutine suspend) for 9.5 seconds.

Senior: đo trước và sau tối ưu​

Chọn một user journey cụ thể: cold startup tới nội dung có thể tương tác, hoặc cuộn feed có ảnh. Đặt metric và điều kiện so sánh trước khi sửa code.

  • Dùng build gần release, cùng thiết bị/dữ liệu/kịch bản; lặp nhiều lần và ghi nhận biến động, nhiệt độ, tác vụ nền.
  • Với Baseline Profile, so sánh compilation mode có/không profile. Đo hành vi thực tế thay vì hứa mức tăng tốc cố định.
  • 120Hz có chu kỳ khoảng 8,3ms, 60Hz khoảng 16,7ms. Trace main thread, RenderThread, GPU và scheduling để tìm deadline bị lỡ.
  • Memory tăng cần phân biệt cache, allocation churn và leak. Với leak, tìm retention path tới đối tượng hết vòng đời và kiểm tra lại sau cleanup.

Bài tập: sửa allocation trong onDraw hoặc ảnh decode quá lớn, rồi đo lại cùng journey. Lưu trace và bảng metric trước/sau để reviewer kiểm tra được.

Nguồn: Macrobenchmark, tạo Baseline Profiles.