Profiling

CPU profiling (samply)

Setup

First you need to install samply. You can install it with:

cargo binstall samply

WARNING

Samply does not work well on macOS. We recommend using Xcode Instruments instead.

Build

To build Rolldown with the information required by samply, you need to build it with:

just build-rolldown-profile

Profiling

After building, you can run Rolldown with the following command to profile CPU usage:

samply record node ./path/to/script-rolldown-is-used.js

If you want to profile the JavaScript part as well, you can pass the required flags to Node:

samply record node --perf-prof --perf-basic-prof --perf-prof-unwinding-info --interpreted-frames-native-stack ./path/to/script-rolldown-is-used.js

CPU profiling (Xcode Instruments)

Setup

First, make sure you have Xcode installed.

Build

To build Rolldown with the information required by Xcode Instruments, you need to build it with:

just build-rolldown-profile

Profiling

After building, you can run Rolldown with the following command to profile CPU usage:

xctrace record --template "Time Profile" --output . --launch -- node ./path/to/script-rolldown-is-used.js

then the output file path will be printed. You can open the file with:

open ./Launch_node_yyyy-mm-dd_hh.mm.ss_hash.trace

Memory profiling

To profile memory usage, you can use heaptrack.

Setup

First you need to install heaptrack and heaptrack-gui. If you are using Ubuntu, you can install it with:

sudo apt install heaptrack heaptrack-gui

WARNING

heaptrack only supports Linux. It works fine on WSL.

Build

To build Rolldown with the information required by heaptrack, you need to build it with:

just build-rolldown-memory-profile

Profiling

After building, you can run Rolldown with the following command to profile memory usage:

heaptrack node ./path/to/script-rolldown-is-used.js

Using asdf or other version manager that uses shims?

In that case, you may need to use the actual path to the Node binary. For example, if you are using asdf, you can run it with:

heaptrack $(asdf which node) ./path/to/script-rolldown-is-used.js

The heaptrack GUI will open automatically after the script finishes running.