1916542 - Avoid JS String conversion in strokeStyle / fillStyle setter, for faster lookup of the cached style for a string

Status: NEW

(Core :: DOM: Bindings (WebIDL), enhancement)

Description

[Markus Stange [:mstange]]

On the Charts-chartjs subtest of Speedometer 3, Firefox currently spends 4x as much time inside the strokeStyle setter as Chrome does.

Firefox: https://share.firefox.dev/4eb551Q (608 samples)
Chrome: https://share.firefox.dev/4e6Grj2 (148 samples, 4x faster)

The strokeStyle setter itself just looks up the string and finds the cached stroke style for it. However, Chrome is much faster at that string lookup.

In Firefox, 40% of the time is spent converting the JS string to an nsCString, and another 40% is spent hashing that string.

Can we do anything to eliminate the string conversion, and maybe even the hashing?

Comment 1

[Jeff Muizelaar [:jrmuizel]]

Here's roughly what Chrome does:

  // Internalize the string so that we can use pointer comparison for equality
  // rather than string comparison.
  v8_string = v8_string->InternalizeString(isolate);
  if (v8_string->Length()) {
    const auto it = color_cache_.Find<ColorCacheHashTranslator>(v8_string);

Comment 2

[Jeff Muizelaar [:jrmuizel]]

Peter, how easy is it for us to get atomized JS strings through our bindings to the C++ code?

Comment 4

[Peter Van der Beken [:peterv]]

It's not trivial. I'll put up a patch I've been trying out. Sadly it requires JSAPI usage outside of the bindings code, which we try to avoid.

Comment 5

[Peter Van der Beken [:peterv]]

Attachment: WIP: Bug 1916542 - Return JS::Handle from unions containing JS types.

Comment 6

[Peter Van der Beken [:peterv]]

Attachment: WIP: Bug 1916542 - OffscreenCanvas simplification.

Comment 7

[Peter Van der Beken [:peterv]]

Attachment: WIP: Bug 1916542 - Add CC helpers for JS::[Tenured]Heap.

Comment 8

[Peter Van der Beken [:peterv]]

Attachment: WIP: Bug 1916542 - Add CC helpers for MruCache.

Comment 9

[Peter Van der Beken [:peterv]]

Attachment: WIP: Bug 1916542 - Avoid JS String conversion in strokeStyle / fillStyle setter, for faster lookup of the cached style for a string.

Comment 10

[Peter Van der Beken [:peterv]]

These patches should work. Need to profile first, and then decide whether we want to do this or not.