Performance FAQ

This page collects some frequently asked questions about evaluating and debugging Flutter’s performance.

• Which performance dashboards have metrics that are related to Flutter?
  • Flutter dashboard on appspot
  • Flutter Skia dashboard
  • Flutter Engine Skia dashboard

• How do I add a benchmark to Flutter?
  • How to write a render speed test for Flutter
  • How to write a memory test for Flutter

• What are some tools for capturing and analyzing performance metrics?
  • Dart DevTools
  • Apple instruments
  • Linux perf
  • Chrome tracing (enter about:tracing in your Chrome URL field)
  • Android systrace (adb systrace)
  • Fuchsia fx traceutil
  • Perfetto
  • speedscope

• My Flutter app looks janky or stutters. How do I fix it?
  • Improving rendering performance

• What are some costly performance operations that I need to be careful with?
  • Opacity, Clip.antiAliasWithSaveLayer, or anything that triggers saveLayer
  • ImageFilter
  • Also see Performance best practices

• How do I tell which widgets in my Flutter app are rebuilt in each frame?
  • Set debugProfileBuildsEnabled true in widgets/debug.dart.
  • Alternatively, change the performRebuild function in widgets/framework.dart to ignore debugProfileBuildsEnabled and always call Timeline.startSync(...)/finish.
  • If you use IntelliJ, a GUI view of this data is available. Select show widget rebuild information, and you’ll visually see which widgets rebuild visually in your IDE.

• How do I query the target frames per second (of the display)?
  • Get the display refresh rate

• How to solve my app’s poor animations caused by an expensive Dart async function call that is blocking the UI thread?
  • Spawn another isolate using the compute() method, as demonstrated in Parse JSON in the background cookbook.

• How do I determine my Flutter app’s package size that a user will download?
  • See Measuring your app’s size

• How do I see the breakdown of the Flutter engine size?
  • Visit the binary size dashboard, and replace the git hash in the URL with a recent commit hash from GitHub engine repository commits.

• How can I take a screenshot of an app that is running and export it as a SKP file?
  • Run flutter screenshot --type=skia --observatory-uri=...
  • Note a known issue viewing screenshots:
    • Issue 21237: Doesn’t record images in real devices.
  • To analyze and visualize the SKP file, check out the Skia WASM debugger.

• How do I retrieve the shader persistent cache from a device?
  • On Android, you can do the following:

    adb shell
    run-as <com.your_app_package_name>
    cp <your_folder> <some_public_folder, e.g., /sdcard> -r
    adb pull <some_public_folder/your_folder>
    

• How do I perform a trace in Fuchsia?
  • See Fuchsia tracing guidelines