Stream: git-wasmtime

Topic: wasmtime / PR #2757 Optimize calling a WebAssembly function

Wasmtime GitHub notifications bot (Mar 23 2021 at 18:41):

alexcrichton opened PR #2757 from fast-call to main:

This commit implements a few optimizations, mainly inlining, that should
improve the performance of calling a WebAssembly function. This code
path can be quite hot depending on the embedding case and we hadn't
really put much effort into optimizing the nitty gritty.

The predominant optimization here is adding #[inline] to trivial
functions so performance is improved without having to compile with LTO.
Another optimization is to call lazy_per_thread_init when traps are
initialized per-thread (when a Store is created) rather than each time
a function is called. The next optimization is to change the unwind
reason in the CallThreadState to MaybeUninit to avoid extra checks
in the default case about whether we need to drop its variants (since in
the happy path we never need to drop it). The final optimization is to
optimize out a few checks when async support is disabled for a small
speed boost.

In a small benchmark where wasmtime calls a simple wasm function my
macOS computer dropped from 110ns to 86ns overhead, a 20% decrease. The
macOS overhead is still largely dominated by the global lock acquisition
and hash table management for traps right now, but I suspect the Linux
overhead is much better (should be on the order of ~30 or so ns).

We still have a long way to go to compete with SpiderMonkey which, in
testing, seem to have ~6ns overhead in calling the same wasm function on
my computer.

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Wasmtime GitHub notifications bot (Mar 23 2021 at 18:49):

fitzgen submitted PR Review.

Wasmtime GitHub notifications bot (Mar 23 2021 at 19:11):

alexcrichton updated PR #2757 from fast-call to main.

Wasmtime GitHub notifications bot (Mar 23 2021 at 20:22):

alexcrichton merged PR #2757.

Last updated: Oct 23 2024 at 20:03 UTC