760954 - View source slower in Firefox 15 (hangs with high cpu for seconds) on some (many?) HTML pages

Status: VERIFIED FIXED

(Toolkit :: View Source, defect)

Description

[Nickolay_Ponomarev]

Attachment: original page demonstrating the slowdown

STR: open attached file, select Tools -> Web developer -> Page source (Cmd+U).

Actual results: the page source is empty for a few seconds, during which Firefox uses 100% cpu doing reflow.

Expected results: view source should display as fast as in Firefox 14.

Regression window points to bug 751841:

Good: http://ftp.mozilla.org/pub/mozilla.org/firefox/tinderbox-builds/mozilla-inbound-macosx64/1338359573/firefox-15.0a1.en-US.mac.dmg
(built from http://hg.mozilla.org/integration/mozilla-inbound/rev/b613ac5ff64a)

Bad: http://ftp.mozilla.org/pub/mozilla.org/firefox/tinderbox-builds/mozilla-inbound-macosx64/1338360714/firefox-15.0a1.en-US.mac.dmg
(built from http://hg.mozilla.org/integration/mozilla-inbound/rev/e98f0fc3d02e)

According the the built-in profiler, with the patch we spend 4.5 seconds on my machine under PresShell::DoReflow, whereas before the patch it was 1 second.

I tried to simplify the page and I see the slowdown with
1) a long line with entity references (")
2) many lines, with or without entity references

Comment 1

[Nickolay_Ponomarev]

Attachment: testcase 1: many lines

Comment 2

[Nickolay_Ponomarev]

Attachment: testcase 2: single line, but many entity references

Comment 3

[Simon Montagu :smontagu]

Attachment: Patch

This possibly needs to be split into two bugs, something like a) performance is bad with lots of elements with unicode-bidi: isolate; b) view-source uses lots of elements with unicode-bidi: isolate.

This is a patch for b), i.e. it fixes the issue with view-source slowdown, but there could be similar slowdown in other cases.

Comment 4

[Simon Montagu :smontagu]

Attachment: Correct diff

Comment 5

[Simon Montagu :smontagu]

I have *no* clue where that first hunk is coming from :(

Comment 6

[Simon Montagu :smontagu]

Attachment: Correct diff

Comment 7

[(no longer active)]

I went ahead and landed the patch: http://hg.mozilla.org/mozilla-central/rev/42f8002ca13b

Comment 8

[Nickolay_Ponomarev]

Thanks for the quick fix! The issue is now fixed for me.