1005249 - Layout Performance Debugging API

Status: RESOLVED WORKSFORME

(Core :: Layout, enhancement, P4)

Description

[Nick Fitzgerald [:fitzgen] [⏰PST; UTC-8]]

There should be a "performance debugging" mode for layout that can be enabled when the devtools are open. It should provide APIs for correlating significant layout events with a specific JS call, CSS rule, or whatever web API triggered the event. Ideally we would be able to give a full stack trace. Perhaps we can use something like the MozExecutionReason being developed for spidermonkey[0].

Off the top of my head, interesting events might include (forgive my lack of knowledge about the right terms and specifics of Layout algorithms):

* Putting an operation in the layout queue (like appending an element to the DOM)

* Forcing the layout queue to be flushed (like checking elem.clientHeight, etc)
  * Would be nice to get the list of operations that were queued (and the associated JS stacks and whatever meta information) that got flushed
  * Would also be great to have timings of how long the flush took

[0] See https://bugzilla.mozilla.org/show_bug.cgi?id=961325

Comment 1

[Gregory Pappas [:gregp]]

Pretty sure the Firefox Profiler does everything mentioned in comment 0.