iOS CPU Profiling

XCode (via Instruments) has a number of built in profiling tools that can easily be used with local or prebuilt engines. This document is focused on creating Flame Graphs. These are not part of XCode but provide a useful way to look at aggregate performance. The process for generating Flame Graphs for iOS/macOS is a bit janky compared to Android Studio however and external tools are necessary.

Setup External Tools

We need to setup the FlameGraph Swift command-line tool. You can either build the tool locally, or use the Mint Package Manager for Swift packages. We'll use Mint in the following example.

Skip the following steps if you have already performed them.

Install Mint

Install Mint via Brew.

brew install mint

Add the Mint bin directory to your path. The following assumes your .rc file is .profile. Adjust as necessary.

echo 'export PATH="$PATH:$HOME/.mint/bin"' >> ~/.profile
source ~/.profile

Install FlameGraph via Mint

mint install lennet/FlameGraph

Capture Profile using Instruments

Use the Time Profiler Xcode template.

Click the red dot to begin and record as much profile data as you want. Press stop to conclude the trace.

Select the thread to investigate, in this case you want io.flutter.raster.

[!IMPORTANT] Make sure to select the trace root.

Copy the trace with the keyboard shortcut (⇧⌘C) or the menu (“Edit” -> “Deep Copy”).

Convert Profile to FlameGraph

On the command line, run FlameGraph to convert the contents of the profile in your pasteboard to an HTML format.

FlameGraph --html output.html

A new browser tab will open with the Flame Graph. It may require some zooming to be useful.