790255 - Unresponsiveness while displaying a large HTML document

Status: NEW

(Core :: Layout, defect)

Description

[Florian Quèze [:florian]]

Thunderbird 15+ supports Twitter, and I've noticed that displaying lots of tweets sometimes takes a lot of time.

The current code adds tweets to the HTML document in batches and stops after 50ms, but to understand what was actually taking CPU time, I commented out that part that stops after 50ms, and displayed a large batch of approximatively 10k tweets at once.

Out of the 50s that takes, 40s seem to be spent doing reflow.

I've saved the generated HTML DOM with DOMi, and fixed the paths so that the same HTML document could be loaded in Firefox, and I profiled it again there.

Loading the HTML document in Firefox from the local disk (file://) or from an http URL the second time (ie after it's been cached locally) makes the Firefox UI unresponsive.
What shows up in the profiler is time spent in nsCSSFrameConstructor and PresShell::ProcessReflowCommands.

I'm not sure if being unresponsive when loading a large (3.6MB) HTML document is expected or not, but in case it's not or in case there are low hanging fruits here, the document I used can be loaded from:
http://queze.net/goinfre/largetimeline/

And here are some profiles:
http://people.mozilla.com/~bgirard/cleopatra/?report=d6bd2dd6fdafde3630264aaf574c42cb01b9d65c
http://people.mozilla.com/~bgirard/cleopatra/?report=a1d5523ba53dd497522fdcaf37b3ab402c1dd74a
http://people.mozilla.com/~bgirard/cleopatra/?report=f571c4dee29ee9b0818586a91245f4878551dd4f

Comment 1

[Boris Zbarsky [:bzbarsky]]

Florian, how long are you seeing pageload take for http://queze.net/goinfre/largetimeline/ ?  I just tried it, and it takes at most 4 seconds for me (granted, on pretty new hardware).

Comment 2

[Florian Quèze [:florian]]

Around 4s too on Firefox (and on a pretty new i7 Macbook Pro).

I haven't figured out yet why it makes such a large difference when it's loaded as a plain HTML file in the browser rather than as lots of chunks added in Tb with calls to appendChild with a documentFragment as paramater, but as it's still unresponsive in the browser and that part can trivially be reproduced, I figured I would still file a bug with the profiles I got from Firefox. Sorry if my previous comment was misleading :-(.

Unfortunately the profiles I uploaded from Thunderbird fail to load because of a JS error in the profiler web UI.
Just in case it gets fixed soon, here's the link to a Tb profile: http://people.mozilla.com/~bgirard/cleopatra/?report=83009d2d95d7e6974b00055ed8fd99fe68809a9d

Comment 3

[Florian Quèze [:florian]]

(In reply to Florian Quèze [:florian] [:flo] from comment #2)

> Just in case it gets fixed soon, here's the link to a Tb profile:
> http://people.mozilla.com/~bgirard/cleopatra/
> ?report=83009d2d95d7e6974b00055ed8fd99fe68809a9d

So actually, this works in a current nightly of Firefox, but doesn't in 15.0 (see bug 790344 for details).