Bug 44173 - Scrolling is slow and stuttery on some long pages (due to accelerated compositing?)
Summary: Scrolling is slow and stuttery on some long pages (due to accelerated composi...
Status: RESOLVED INVALID
Alias: None
Product: WebKit
Classification: Unclassified
Component: Layout and Rendering (show other bugs)
Version: 528+ (Nightly build)
Hardware: PC OS X 10.5
: P2 Normal
Assignee: Nobody
URL: http://blogs.msdn.com/b/ntdebugging/
Keywords: InRadar
Depends on:
Blocks:
 
Reported: 2010-08-18 06:48 PDT by Adam Roben (:aroben)
Modified: 2010-08-18 09:54 PDT (History)
2 users (show)

See Also:

Attachments
testcase (3.32 MB, application/x-webarchive)
2010-08-18 06:49 PDT, Adam Roben (:aroben) 		no flags Details
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Description Adam Roben (:aroben) 2010-08-18 06:48:35 PDT 
To reproduce:

1. Open the attached Web Archive
2. Drag the scrollbar down to the bottom

When you reach about 2/3 of the way down the page (in the middle of the "Storport ETW Logging to Measure Requests Made to a Disk Unit" article), scrolling becomes slow and stutters. The scroll thumb visibly lags behind the mouse.

I've only tested with Safari 5.0.1 on SnowLeopard.
Comment 1 Adam Roben (:aroben) 2010-08-18 06:49:07 PDT 
Created attachment 64701 [details]
testcase
Comment 2 Adam Roben (:aroben) 2010-08-18 07:08:08 PDT 
<rdar://problem/8324086>
Comment 3 Adam Roben (:aroben) 2010-08-18 09:46:24 PDT 
Here's an even easier to reproduce case:

1. Go to http://trac.webkit.org/browser/trunk/WebKit/win/WebView.cpp?rev=58900#L946
2. Drag the scroll bar thumb

Scrolling is horribly slow. Tiles of the page visibly repaint as you go.

Turning off accelerated compositing brings performance back to acceptable levels.
Comment 4 Adam Roben (:aroben) 2010-08-18 09:54:00 PDT 
Whoops, I had an extension installed that turned on accelerated compositing for all <img> elements. Without that extension these pages don't go into accelerated compositing mode. Simon Fraser assures me that we already have bugs that cover the symptoms I was seeing on pages that legitimately use accelerated compositing, so I'm going to close this bug.