wasmtime / PR #9611 Cranelift: add option to use new sing... · git-wasmtime

Stream: git-wasmtime

Topic: wasmtime / PR #9611 Cranelift: add option to use new sing...

Wasmtime GitHub notifications bot (Nov 15 2024 at 07:41):

cfallin opened PR #9611 from cfallin:single-pass-regalloc to bytecodealliance:main:

In bytecodealliance/regalloc2#181, @d-sonuga added a fast single-pass algorithm option to regalloc2, in addition to its existing backtracking allocator. This produces code much more quickly, at the expense of code quality. Sometimes this tradeoff is desirable (e.g. when performing a debug build in a fast-iteration development situation, or in an initial JIT tier).

This PR adds a Cranelift option to select the RA2 algorithm, plumbs it through to a Wasmtime option, and adds the option to Wasmtime fuzzing as well.

An initial compile-time measurement in Wasmtime: spidermonkey.wasm builds in 1.383s with backtracking (existing algorithm), and 1.065s with single-pass. The resulting binary runs a simple Fibonacci benchmark in 2.060s with backtracking vs. 3.455s with single-pass.

Hence, the single-pass algorithm yields a 23% compile-time reduction, at the cost of a 67% runtime increase.

Fixes #9596.

Depends on bytecodealliance/regalloc2#201 and the corresponding RA2 release; this PR has a local
path-override and so will fail to build in CI until I update it post-RA2-release.

Wasmtime GitHub notifications bot (Nov 15 2024 at 07:41):

cfallin requested wasmtime-fuzz-reviewers for a review on PR #9611.

Wasmtime GitHub notifications bot (Nov 15 2024 at 07:41):

cfallin requested alexcrichton for a review on PR #9611.

Wasmtime GitHub notifications bot (Nov 15 2024 at 07:41):

cfallin requested wasmtime-compiler-reviewers for a review on PR #9611.

Wasmtime GitHub notifications bot (Nov 15 2024 at 07:41):

cfallin requested abrown for a review on PR #9611.

Wasmtime GitHub notifications bot (Nov 15 2024 at 07:41):

cfallin requested wasmtime-core-reviewers for a review on PR #9611.

Wasmtime GitHub notifications bot (Nov 15 2024 at 07:41):

cfallin requested wasmtime-default-reviewers for a review on PR #9611.

Wasmtime GitHub notifications bot (Nov 15 2024 at 08:47):

Amanieu commented on PR #9611:

Should this selection be automatic with opt_level=none?

Wasmtime GitHub notifications bot (Nov 15 2024 at 08:47):

github-actions[bot] commented on PR #9611:

Subscribe to Label Action

cc @fitzgen

<details>
This issue or pull request has been labeled: "cranelift", "cranelift:area:machinst", "cranelift:meta", "fuzzing", "wasmtime:api", "wasmtime:config"

Thus the following users have been cc'd because of the following labels:

fitzgen: fuzzing

To subscribe or unsubscribe from this label, edit the <code>.github/subscribe-to-label.json</code> configuration file.

Learn more.
</details>

Wasmtime GitHub notifications bot (Nov 15 2024 at 08:53):

bjorn3 commented on PR #9611:

In that case we should probably get an opt level between none and speed which uses the better regalloc but keeps egraph optimizations disabled given that the better regalloc has a significantly higher improvement to runtime performance than egraph optimizations.

Wasmtime GitHub notifications bot (Nov 15 2024 at 09:45):

github-actions[bot] commented on PR #9611:

Label Messager: wasmtime:config

It looks like you are changing Wasmtime's configuration options. Make sure to
complete this check list:

[ ] If you added a new Config method, you wrote extensive documentation for
it.

<details>

Our documentation should be of the following form:

```text
Short, simple summary sentence.

More details. These details can be multiple paragraphs. There should be
information about not just the method, but its parameters and results as
well.

Is this method fallible? If so, when can it return an error?

Can this method panic? If so, when does it panic?

Example

Optional example here.
```

</details>

[ ] If you added a new Config method, or modified an existing one, you
ensured that this configuration is exercised by the fuzz targets.

<details>

For example, if you expose a new strategy for allocating the next instance
slot inside the pooling allocator, you should ensure that at least one of our
fuzz targets exercises that new strategy.

Often, all that is required of you is to ensure that there is a knob for this
configuration option in [wasmtime_fuzzing::Config][fuzzing-config] (or one
of its nested structs).

Rarely, this may require authoring a new fuzz target to specifically test this
configuration. See [our docs on fuzzing][fuzzing-docs] for more details.

</details>

[ ] If you are enabling a configuration option by default, make sure that it
has been fuzzed for at least two weeks before turning it on by default.

[fuzzing-config]: https://github.com/bytecodealliance/wasmtime/blob/ca0e8d0a1d8cefc0496dba2f77a670571d8fdcab/crates/fuzzing/src/generators.rs#L182-L194
[fuzzing-docs]: https://docs.wasmtime.dev/contributing-fuzzing.html

<details>

To modify this label's message, edit the <code>.github/label-messager/wasmtime-config.md</code> file.

To add new label messages or remove existing label messages, edit the
<code>.github/label-messager.json</code> configuration file.

Learn more.

</details>

Wasmtime GitHub notifications bot (Nov 15 2024 at 16:10):

alexcrichton submitted PR review:

:tada: nice!

I'm ambivalent myself on the defaults for O0 and could go either way.

Wasmtime GitHub notifications bot (Nov 15 2024 at 17:23):

cfallin updated PR #9611.

Wasmtime GitHub notifications bot (Nov 15 2024 at 17:24):

cfallin edited PR #9611:

In bytecodealliance/regalloc2#181, @d-sonuga added a fast single-pass algorithm option to regalloc2, in addition to its existing backtracking allocator. This produces code much more quickly, at the expense of code quality. Sometimes this tradeoff is desirable (e.g. when performing a debug build in a fast-iteration development situation, or in an initial JIT tier).

This PR adds a Cranelift option to select the RA2 algorithm, plumbs it through to a Wasmtime option, and adds the option to Wasmtime fuzzing as well.

An initial compile-time measurement in Wasmtime: spidermonkey.wasm builds in 1.383s with backtracking (existing algorithm), and 1.065s with single-pass. The resulting binary runs a simple Fibonacci benchmark in 2.060s with backtracking vs. 3.455s with single-pass.

Hence, the single-pass algorithm yields a 23% compile-time reduction, at the cost of a 67% runtime increase.

Fixes #9596.

Wasmtime GitHub notifications bot (Nov 15 2024 at 17:34):

cfallin updated PR #9611.

Wasmtime GitHub notifications bot (Nov 15 2024 at 17:38):

cfallin updated PR #9611.

Wasmtime GitHub notifications bot (Nov 15 2024 at 17:40):

cfallin commented on PR #9611:

For now at least, I think I'd prefer to keep it an opt-in default -- let's let it bake in wasmtime's continuous fuzzing for a little longer. We can always switch the default later.

@alexcrichton updated to add cargo-vet, could you rubber-stamp the new commit? Also fixed silly issues in fuzz build (which I never test beforehand because Ocaml; I should fix my setup!).

Wasmtime GitHub notifications bot (Nov 15 2024 at 17:47):

cfallin updated PR #9611.

Wasmtime GitHub notifications bot (Nov 15 2024 at 17:55):

alexcrichton submitted PR review:

Looks good!

For fuzzing you can also build the fuzzers with --no-default-features to turn off the ocaml integration.

Wasmtime GitHub notifications bot (Nov 15 2024 at 18:15):

cfallin merged PR #9611.

Last updated: Nov 22 2024 at 16:03 UTC