One profiler supported by Wasmtime is
samply for Linux and macOS. As of 17th July 2023, the
latest version of samply (on crates.io) is 0.11.0 which does not seem to support perfmaps. To use this, you either need a
newer version of samply, if by the time you read this, a newer version has been released, or you can build samply from source.
Simple profiling support with
samply generates a "perfmap" file that the
samply CLI will
automatically look for, when running into unresolved symbols. This requires runtime support from
Wasmtime itself, so you will need to manually change a few things to enable profiling support in
your application. Enabling runtime support depends on how you're using Wasmtime:
Rust API - you'll want to call the [
Config::profiler] method with
ProfilingStrategy::PerfMapto enable profiling of your wasm modules.
C API - you'll want to call the
wasmtime_config_profiler_setAPI with a
Command Line - you'll want to pass the
--profile=perfmapflag on the command line.
Once perfmap support is enabled, you'll use
samply record like usual to record
your application's performance.
For example if you're using the CLI, you'll execute:
$ samply record wasmtime --profile=perfmap foo.wasm
This will record your application's performance and open the Firefox profiler UI to view the
results. It will also dump its own profile data to a json file (called
profile.json) in the current directory.
Note that support for perfmap is still relatively new in Wasmtime, so if you have any problems, please don't hesitate to file an issue!