1852233 - A JS utility takes 2x more time than Chrome and we spend a lot of time around GC. All the rest is spent in Baseline.

Status: RESOLVED FIXED

(Core :: JavaScript Engine, task, P3)

Description

[Mayank Bansal]

Go to http://xem.github.io/hex/viewer_input_es6.html
Choose any local file (atleast 1 MB in size) from your machine

Chrome: https://share.firefox.dev/45JMiH8 (8 seconds)
Nightly: https://share.firefox.dev/3sNQpDB (18 seconds)

Comment 1

[Mayank Bansal]

Attachment: sample_testing_file.html

Comment 2

[Mayank Bansal]

If you take a larger (15MB-ish) file, the profile looks like this:

Nightly: https://share.firefox.dev/44DA1Tm (2 minutes)
Chrome: https://share.firefox.dev/3PqY43v (35 seconds)

So looks like as the file size increases, we spend increasingly more time around GC, while the main js part takes roughly the same time in both chrome and nightly.

Comment 3

[Mayank Bansal]

I tried a autoland build, and the GC part is completely gone from the profile!

Comment 4

[Mayank Bansal]

profile: https://share.firefox.dev/3Rvrxe3

The gc part is completely fixed.

Is there any interest in investigating/fixing the remaining JS part where all the time is spent in Baseline?

Comment 5

[Jan de Mooij [:jandem]]

(In reply to Mayank Bansal from comment #4)

Is there any interest in investigating/fixing the remaining JS part where all the time is spent in Baseline?

We spend most of the time doing name lookups (BindName, GetName) in Baseline because the script has a with statement:

h = '<pre>';
with(new FileReader) readAsArrayBuffer(files[0]), onload = s => {
    for (i in u = new Uint8Array(result)) h += (i % 16 ? ' ' : '\n' + (1e7 + (+i)[t = 'toString'](16)).slice(-8) + ' | ') + (0 + u[i][t](16)).slice(-2);
    outerHTML = h
}

This is really poorly written JS code.

We don't Warp compile the onload arrow function because Warp doesn't support JSOp::GetBoundName yet. That's fixable, but it's also low priority and this website would still be pretty slow due to the slow name lookups.

Comment 6

[Mayank Bansal]

Sounds like the remaining parts are a known thing (and probably tracked elsewhere), and we are comparable to Chrome now. The GC issue has been fixed.
I will close this bug. Thanks!

Comment 7

[Mayank Bansal]

FWIW, the profile in latest Nightly : https://share.firefox.dev/3BOQn37
All the time is in ion now.
I will give credit to bug 1916185