Stream: wasmtime

Topic: application caching / performance

Johannes Becker (Mar 23 2023 at 21:44):

Hi all, I have not yet advanced very deeply into the wasmtime codebase, but we are currently building a little runner agent for wasm programs that leads us to believe that there is some interesting performance optimization going on that we don't fully understand. I'd appreciate any pointers that would help us understand what is going on here.
We have a little ruby.wasm Hello world that looks like this when run via Wasmtime:

$ time wasmtime build/ruby-example.wasm
Hello, world! This is Ruby. 🟥💎
wasmtime build/ruby-example.wasm  15.48s user 0.64s system 168% cpu 9.579 total
$ time wasmtime build/ruby-example.wasm
Hello, world! This is Ruby. 🟥💎
wasmtime build/ruby-example.wasm  0.21s user 0.03s system 98% cpu 0.237 total

...clearly there is some caching going on.
Running our own test runner (which internally runs wasmtime) we get something like this:

$ time cargo run --release --bin test-runner -- ../wasm-samples/build/ruby-example.wasm
cargo run --release --bin test-runner --   15.59s user 0.65s system 106% cpu 15.305 total
$ time cargo run --release --bin test-runner -- ../wasm-samples/build/ruby-example.wasm
cargo run --release --bin test-runner --   15.35s user 0.62s system 167% cpu 9.553 total

Clearly there is some caching possible, but not enabled. What's the best way to get the same caching performance when using wasmtime as a module?

Robin Brown (Mar 23 2023 at 22:06):

There's some info on the cli cache system here
https://docs.wasmtime.dev/cli-cache.html#how-does-the-cache-work
It looks like this API might correspond to it in the embedding create
https://docs.rs/wasmtime/latest/wasmtime/struct.Config.html#method.cache_config_load_default

Robin Brown (Mar 23 2023 at 22:17):

You could look into calling precompile_module yourself if you want more control.
https://docs.rs/wasmtime/latest/wasmtime/struct.Engine.html#method.precompile_module

Peter Huene (Mar 24 2023 at 00:33):

There is also the wasmtime compile subcommand.

Last updated: Dec 23 2024 at 14:03 UTC