Profiling

CPU profiling (samply)

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

bash

cargo binstall samply

::: warning

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

:::

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

shell

just build-rolldown-profile

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

shell

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:

shell

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

First, make sure you have Xcode installed.

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

shell

just build-rolldown-profile

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

shell

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:

shell

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

To profile memory usage, you can use heaptrack.

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

bash

sudo apt install heaptrack heaptrack-gui

::: warning

heaptrack only supports Linux. It works fine on WSL.

:::

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

shell

just build-rolldown-memory-profile

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

shell

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

::: tip 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:

shell

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

:::

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