18dd82ba7d
This commit is intended to be a perf improvement for instantiation of modules with lots of functions. Previously the `lookup_shared_signature` callback was showing up quite high in profiles as part of instantiation. As some background, this callback is used to translate from a module's `SignatureIndex` to a `VMSharedSignatureIndex` which the instance stores. This callback is called for two reasons, one is to translate all of the module's own types into `VMSharedSignatureIndex` for the purposes of `call_indirect` (the translation of that loads from this table to compare indices). The second reason is that a `VMCallerCheckedAnyfunc` is prepared for all functions and this embeds a `VMSharedSignatureIndex` inside of it. The slow part today is that the lookup callback was called once-per-function and each lookup involved hashing a full `WasmFuncType`. Albeit our hash algorithm is still Rust's default SipHash algorithm which is quite slow, but we also shouldn't need to re-hash each signature if we see it multiple times anyway. The fix applied in this commit is to change this lookup callback to an `enum` where one variant is that there's a table to lookup from. This table is a `PrimaryMap` which means that lookup is quite fast. The only thing we need to do is to prepare the table ahead of time. Currently this happens on the instantiation path because in my measurments the creation of the table is quite fast compared to the rest of instantiation. If this becomes an issue, though, we can look into creating the table as part of `SigRegistry::register_module` and caching it somewhere (I'm not entirely sure where but I'm sure we can figure it out). There's in generally not a ton of efficiency around the `SigRegistry` type. I'm hoping though that this fixes the next-lowest-hanging-fruit in terms of performance without complicating the implementation too much. I tried a few variants and this change seemed like the best balance between simplicity and still a nice performance gain. Locally I measured an improvement in instantiation time for a large-ish module by reducing the time from ~3ms to ~2.6ms per instance.
wasmtime
A standalone runtime for WebAssembly
A Bytecode Alliance project
Guide | Contributing | Website | Chat
Installation
The Wasmtime CLI can be installed on Linux and macOS with a small install script:
$ curl https://wasmtime.dev/install.sh -sSf | bash
Windows or otherwise interested users can download installers and binaries directly from the GitHub Releases page.
Example
If you've got the Rust compiler installed then you can take some Rust source code:
fn main() {
println!("Hello, world!");
}
and compile/run it with:
$ rustup target add wasm32-wasi
$ rustc hello.rs --target wasm32-wasi
$ wasmtime hello.wasm
Hello, world!
Features
-
Lightweight. Wasmtime is a standalone runtime for WebAssembly that scales with your needs. It fits on tiny chips as well as makes use of huge servers. Wasmtime can be embedded into almost any application too.
-
Fast. Wasmtime is built on the optimizing Cranelift code generator to quickly generate high-quality machine code at runtime.
-
Configurable. Whether you need to precompile your wasm ahead of time, generate code blazingly fast with Lightbeam, or interpret it at runtime, Wasmtime has you covered for all your wasm-executing needs.
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WASI. Wasmtime supports a rich set of APIs for interacting with the host environment through the WASI standard.
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Standards Compliant. Wasmtime passes the official WebAssembly test suite, implements the official C API of wasm, and implements future proposals to WebAssembly as well. Wasmtime developers are intimately engaged with the WebAssembly standards process all along the way too.
Language Support
You can use Wasmtime from a variety of different languages through embeddings of the implementation:
- Rust - the
wasmtimecrate - C - the
wasm.h,wasi.h, andwasmtime.hheaders - Python - the
wasmtimePyPI package - .NET - the
WasmtimeNuGet package - Go - the
wasmtime-gorepository
Documentation
📚 Read the Wasmtime guide here! 📚
The wasmtime guide is the best starting point to learn about what Wasmtime can do for you or help answer your questions about Wasmtime. If you're curious in contributing to Wasmtime, it can also help you do that!
It's Wasmtime.