1607559 - Slow performance of inline source maps

Status: VERIFIED FIXED

(DevTools :: Debugger, defect, P2)

Description

[:Harald Kirschner :digitarald]

Attachment: console-source-map-errors.log

The local dev version of hubs (https://github.com/mozilla/hubs) uses inline source maps.

Firefox takes 40+ seconds to load them. https://perfht.ml/305hcsz

Chrome is instant.

The prod build, https://hubs.mozilla.com/, does not excibit the same issue.

There are also some non-readable source map errors which might be related, see attached logs.

Comment 1

[:Harald Kirschner :digitarald]

Logan, could you help with root cause analysis?

Comment 2

[Jason Laster [:jlast]]

So, it looks like the problem is we're spending a ton of time parsing the sources. I can also dig a bit more into this.

Comment 3

[Logan Smyth [:loganfsmyth]]

@Harald
I filed https://bugzilla.mozilla.org/show_bug.cgi?id=1607639 for the exceptions you posted, since those would be unrelated to performance issues.

Since Jason already started, Ill leave it to him to dig into the perf more.

Comment 4

[:Harald Kirschner :digitarald]

20:08.78 INFO: Last good revision: 36535c33a0c0fcfe26409f2c4fccc134f092bd07
20:08.78 INFO: First bad revision: 78a3f864177fe193bb6ee4a14b81cbe84e25435c
20:08.78 INFO: Pushlog:
https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=36535c33a0c0fcfe26409f2c4fccc134f092bd07&tochange=78a3f864177fe193bb6ee4a14b81cbe84e25435c

Which makes it bug 1558111. Before the source map loaded in less than 5sec. Jason recommended that this low-level change might be better suited for Logan to analyze.

Comment 5

[Logan Smyth [:loganfsmyth]]

Attachment: Bug 1607559 - Part 1: Do not replace the global URL with whatwg-url. r=jlast!

By loading whatwg-url like this, we replace the worker global URL property
(among others), which means that code that uses URL and expects it to be the
version that is built into Firefox may not get what they expect.

Comment 6

[Logan Smyth [:loganfsmyth]]

Attachment: Bug 1607559 - Part 2: Avoid perf issue with data: URLs for inlined source-maps. r=jlast!

Depends on D69933

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/c810f015eef6
Part 1: Do not replace the global URL with whatwg-url. r=jlast
https://hg.mozilla.org/integration/autoland/rev/d06eff418943
Part 2: Avoid perf issue with data: URLs for inlined source-maps. r=jlast

Comment 8

[Andreea Pavel [:apavel]]

https://hg.mozilla.org/mozilla-central/rev/c810f015eef6
https://hg.mozilla.org/mozilla-central/rev/d06eff418943

Comment 9

[Cristian Fogel [:cfogel]]

Confirmed issue with 76.0 on macOS 10.15.3 comparing console errors up.
Fix verified with 77.0b4 on Windows 10, macOS 10.15.3, Ubuntu 20.