[webkit-qt] Performance (regression?) of window.requestAnimationFrame
milian.wolff at kdab.com
Wed Mar 13 10:24:14 PDT 2013
As you might have seen on IRC recently, I have hit a big issue in QtWebKit
when using window.requestAnimationFrame (rAF): Apparently, it triggers a full
repaint of the web view which can lead to abysmal performance.
To reproduce, see this test code: http://paste.kde.org/~mwolff/695234/
If I open it in Chromium, I cannot notice any performance impact, nor do I see
a load spike in ksysguard/top or similar.
Now, doing the same in MiniBrowser I see that X starts to use ~20% of CPU and
MiniBrowser 10%. My system becomes noticeably slugglish (I use KWin as window
compositor with GPU accelleration enabled). On an embedded device we see a
demo app using >50% CPU constantly as soon as it uses rAF.
Also looking at the timeline tab in the developer console yields these
In MiniBrowser: http://imagebin.org/249849
In Chromium: http://imagebin.org/249848
Looking at a cachegrind of MiniBrowser with the above file I see tons of calls
In the code I found this:
updateViewport(); // <-- does this trigger a repaint of everything?
Furthermore I experimented with the TweenMax  JS library and reproduced the
performance issues there. Interestingly enough, disabling its support for rAF
via TweenMax.ticker.useRAF(false); made the animations much smoother and
greatly reduced the System/CPU load. This is in so far interesting, as
TweenMax uses a window.setTimeout based fallback in such cases. Afaik rAF was
initially introduced to *improve* the performance of animations compared to
the timer approach, no?
All this combined brings me to the conclusion that QtWebKit as-is has a big
performance issue with rAF. On IRC it was said that kbalazs is looking into
this but I could not get hold of him. Is this true? What's the status? Is
there anything I could do?
On IRC there was also the mention of "the operationqueue patch" and that it
may have introduced a regression. Which patch exactly is this so I could try
to revert to a time before it and see whether it actually is the reason?
Milian Wolff | milian.wolff at kdab.com | Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel. Germany +49-30-521325470, Sweden (HQ) +46-563-540090
KDAB - Qt Experts - Platform-independent software solutions
-------------- next part --------------
A non-text attachment was scrubbed...
Size: 198 bytes
Desc: This is a digitally signed message part.
More information about the webkit-qt