[Webkit-unassigned] [Bug 106309] New: [Qt] High CPU load with CSS animations in Qt5's WebKit compared to Qt4.8

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=106309

           Summary: [Qt] High CPU load with CSS animations in Qt5's WebKit
                    compared to Qt4.8
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: PC
        OS/Version: Windows 7
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: WebKit Qt
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: bugzilla at kaffeeschluerfer.com


Created an attachment (id=181660)
 --> (https://bugs.webkit.org/attachment.cgi?id=181660&action=review)
ZIP file with test program and test page

Visual Studio 2010 and Windows 7 64bit (as well as Windows XP 32bit)

A page with a simple CSS animation has (see attachment)
- with Qt4.8's QtWebKit: almost no CPU load  (no matter which machine and windows version)
- with Qt5's QtWebKit:
  - CPU load of 40%-60%  (virtual machine with WinXP and single core emulation)
  - CPU load of 20%-30% (real PC with Win 7 64bit, Intel Xeon CPU X3470)

If you toggle the CSS animation off or resize the window so that you will not see the animation, the CPU load drops to almost zero.

I attached a test program which initially shows an html page (also included). You can also take the fancybrowser example to see the much higer CPU load.

The attached html page includes a very simple CSS animation. Normally we have more sophisticated animations with pictures which can cause even higher CPU loads. On a single core machine our _real_ application is not working anymore, because the UI application is taking 100% CPU and all other processes are stuck! Apart from a much higher memory consumption, this is a stopper for us to go on with Qt5.

Of course the CPU load depends on CPU and OS. If you measure the load be sure that you do NOT only use the number from the Task Manager in the Process tab. Because what you see there is the CPU load divided by the number of CPU cores, i.e. the number there is much lesser. Take a look at the Performance tab, there you can see the load for every core.

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