118555 2013-07-11 02:12:20 -0700 Do not update compositing layers when the style is forced from JavaScript 2013-07-11 11:12:56 -0700 1 1 1 Unclassified WebKit Layout and Rendering 528+ (Nightly build) Unspecified Unspecified RESOLVED DUPLICATE 84393 P2 Normal --- 1 achicu webkit-unassigned simon.fraser thorton oldest_to_newest 907571 0 achicu 2013-07-11 02:12:20 -0700 Some websites trigger many relayouts from JS. Each time the layout is triggered, Document::recalcStyle will call view()->updateCompositingLayersAfterStyleChange(). That happens even if we are only going to repaint only once when the JS execution is finished. However, there's no need to update the composited layers to answer questions from JS, so we could postpone it until the very last moment and compute the layers only once. 907572 1 achicu 2013-07-11 02:17:06 -0700 The issue is visible on http://www.milwaukeepolicenews.com . Scrolling is really bad because the JavaScript listens for scroll events and updates the layout every single frame. There are at least 10-15 style updates for each frame and each update will recalculate the compositing requirements of the layers. RenderLayerCompositor::updateCompositingLayers takes 96% of the total time while scrolling the document. 907718 2 simon.fraser 2013-07-11 11:12:56 -0700 Yep, aware of this. We have another bug:84393 *** This bug has been marked as a duplicate of bug 84393 ***