1356070 - https://doc.servo.org/webrender/ hangs the main thread

Status: RESOLVED DUPLICATE of bug 1145297

(Core :: JavaScript Engine: JIT, defect)

Description

[Mike Conley (:mconley) (:⚙️)]

Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:55.0) Gecko/20100101 Firefox/55.0 (20170412030252)

STR:

1) Visit https://doc.servo.org/webrender/

ER:

The page should render fine and the main thread in the content process shouldn't be blocked.

AR:

I get the "a page might be slowing down your browser" notification warning because the page is running JavaScript like crazy.

Here's a profile: https://perfht.ml/2p8kFql

We seem to be doing a lot of work inside search-index.js, doing some JIT stuff. Unsure if this is the right component, but thought I'd start somewhere.

Strangely, this doesn't seem to affect either Safari or Chrome.

Comment 1

[(no longer active)]

This happens with the profiler turned on.

Comment 2

[Markus Stange [:mstange]]

This is our old friend js::PCToLineNumber. We call it on the sampler thread we've paused the main thread, and it's taking a very long time, probably because it's doing a linear search on a single line of minified JavaScript. Then we unpause the main thread, realize we should be taking another sample, and pause it again.