Wasmtime GitHub notifications bot (Jul 14 2025 at 15:35): Wasmtime GitHub notifications bot (Jul 14 2025 at 15:35):adambratschikaye opened issue #11236:
When benchmarking our upgrade to wasmtime 34 we found a regression when it comes to accessing wasm memory in the host. Here's a repo with a some benchmarks with a Wasm module that calls a host function in a loop: https://github.com/adambratschikaye/wasmtime-memory-regression
When the host function accesses the Wasm memory there's a ~30% slowdown when switching from wasmtime 33.0.1 to 34.0.1 (just run cargo bench with both versions to see the difference). When the host function doesn't do anything the performance is unchanged.
Going through a git bisect on the wasmtime repo, it seemed that the regression was coming from https://github.com/bytecodealliance/wasmtime/pull/10877.
Versions and Environment
Operating system: Ubuntu 24.04
Architecture: x64
Wasmtime GitHub notifications bot (Jul 14 2025 at 15:35):adambratschikaye added the bug label to Issue #11236.
Wasmtime GitHub notifications bot (Jul 14 2025 at 21:03):alexcrichton removed the bug label from Issue #11236.
Wasmtime GitHub notifications bot (Jul 14 2025 at 21:03):alexcrichton added the wasmtime:api label to Issue #11236.
Wasmtime GitHub notifications bot (Jul 14 2025 at 21:03):alexcrichton added the performance label to Issue #11236.
Wasmtime GitHub notifications bot (Jul 14 2025 at 21:03):alexcrichton closed issue #11236:
When benchmarking our upgrade to wasmtime 34 we found a regression when it comes to accessing wasm memory in the host. Here's a repo with a some benchmarks with a Wasm module that calls a host function in a loop: https://github.com/adambratschikaye/wasmtime-memory-regression
When the host function accesses the Wasm memory there's a ~30% slowdown when switching from wasmtime 33.0.1 to 34.0.1 (just run cargo bench with both versions to see the difference). When the host function doesn't do anything the performance is unchanged.
Going through a git bisect on the wasmtime repo, it seemed that the regression was coming from https://github.com/bytecodealliance/wasmtime/pull/10877.
Versions and Environment
Operating system: Ubuntu 24.04
Architecture: x64
Wasmtime GitHub notifications bot (Jul 14 2025 at 21:03):alexcrichton commented on issue #11236:
I confirmed locally that https://github.com/bytecodealliance/wasmtime/pull/11235 recovered the performance here, so I'm going to close this, but if anything else comes up definitely feel free to comment here or open a new issue
Last updated: Dec 06 2025 at 06:05 UTC