272190 - Slow scrolling because of XGetImage on page with hidden fixed-pos elements

Status: NEW

(Core :: Web Painting, defect)

Description

[Boris Zbarsky [:bzbarsky]]

Filed as a Unix-only followup to bug 203439.  It looks like nsBlender::Blend()'s
attempt to lock the drawing surface forces a gdk_image_get(), which is what
takes up almost all the time on this testcase.

I don't know whether using Cairo will help here or not, but scrolling is pretty
painfully slow in current trunk builds...

Comment 1

[Adrian Yee]

Here's another test case which really exaggerates the problem (or possibly a
related one):

http://devrandom.com/test/firefox/slowfixedscroll.html

Comment 2

[Adrian Yee]

Well that's weird, it seems to only scroll really slowly when I have the page
that I made the test case from open (in another tab or window):

http://www.markboulton.co.uk

Comment 3

[Wayne Mery (:wsmwk)]

(In reply to comment #1)
> Here's another test case which really exaggerates the problem (or possibly a
> related one):
> 
> http://devrandom.com/test/firefox/slowfixedscroll.html

this also scrolls slowly in windows.

odd "braking" behavior when these get near the top and bottom (but more noticable with these two)
http://www.markboulton.co.uk/
http://gamma.nic.fi/~tapio18/Opetus/index2.php3

Comment 4

[Boris Zbarsky [:bzbarsky]]

> this also scrolls slowly in windows.

Anything you see on Windows is not this bug.  This bug is about a specific Linux-only issue found by profiling.

Note that if you're testing on trunk you should keep in mind that fixed-position stuff is generally slow on trunk right now; there's an existing bug on that.  But it's not _this_ bug.

vlad, how does cairo handle this testcase?

Comment 5

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

It seems to scroll fine, even over a remote X connection talking to a cygwin X server.  However, there is some sort of problem at the very top of the page, where rendering just freezes until you scroll down a little ways; not sure what the problem is there (I don't think it's related).

Comment 6

[Boris Zbarsky [:bzbarsky]]

Well, I scrolled around a bit in a current trunk optimized cairo build.  I see a lot of painting and such in the profile and things are very laggy.  Not sure whether it's better or worse than the non-cairo build...

vlad, note that fixed-pos stuff was broken in the build you tested, so you might want to retest a current build.