[Webkit-unassigned] [Bug 28392] Scrolling a Google Spreadsheet slower than Firefox (much worse on Windows)

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=28392


James Robinson <jamesr at chromium.org> changed:

           What    |Removed                     |Added
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                 CC|                            |jamesr at chromium.org




--- Comment #1 from James Robinson <jamesr at chromium.org>  2009-09-08 17:29:54 PDT ---
I did some investigation of this and it appears that in WebKit the page's
onscroll handler is causing a nontrivial amount of deferred layout to happen
which causes the deferred paint to be delayed by 100+ms after the scroll
happens.  The sequence looks like this (WinXP in VMWare, Chromium, 500 row
spreadsheet, each entry is a separate dispatch off the event loop):

0.) scroll event fires, handler set scrollTop on some element
1.) deferred layout runs for ~25ms
2.) more deferred layout, another ~25ms
3.) ... repeat 3 more times
6.) paint finally happens (~20ms)

It makes sense that the hot paths in the profiler are all in layout - there's a
very large table in the page that apparently has its layout invalidated by
javascript.  The odd thing is that FireFox doesn't exhibit this slowdown -
either they aren't doing this layout, they are doing it after the paint, or the
page is not invalidating layout for FFx while scrolling.

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