Bug 228833 – REGRESSION (r268932): CPU usage higher than expected with sibling elements running WebAnimations

• Component: Animations
• Status: RESOLVED FIXED

[Liam DeBeasi]

Created attachment 434994 [details]
Code reproduction

When using Web Animations, WebKit continually invalidates + recalculates style and paints even when using only transform or opacity.

I can reproduce this issue in iOS 14.5+ and cannot reproduce this issue in iOS 14.4 and older which is why I think this is a performance regression.

Steps to reproduce:

1. Open code reproduction on an iPhone running iOS 14.5 or newer. You should see two blue circles translating up the page. This animation will run continuously.
2. Open Dev Tools and take a Timeline recording. You should notice that WebKit is continually painting and invalidating/recalculating styles. You should also notice that both the CPU usage and energy impact are moderate to high.
4. Repeat steps 1-2 on a device running iOS 14.4. You should notice that WebKit does not continually paint and invalidate/recalculate styles. You should also notice that both the CPU usage and energy impact are low.

Expected Behavior:

I would expect that WebKit does not paint and invalidate/recalculate styles on a running animation that can be hardware accelerated.

Actual Behavior:

WebKit paints and invalidates/recalculates styles on a running animation that can be hardware accelerated.

Other Information:

- This has significant performance implications for any website making use of animations in Safari/WebKit as the main thread is constantly performing work. Additionally, this increases the strain on the battery resulting in the battery getting drained faster.
- This does not reproduce in Chrome or Firefox.

[Liam DeBeasi]

Created attachment 434995 [details]
iOS 14.5 timeline

Added Safari Timeline for code reproduction on iOS 14.5

[Liam DeBeasi]

Created attachment 434996 [details]
iOS 14.4 Timeline

Added Safari Timeline for code reproduction on iOS 14.4

[Simon Fraser (smfr)]

I can confirm. Also on macOS, inspector shows "composite" every frame on iOS and macOS

[Radar WebKit Bug Importer]

<rdar://problem/81573075>

[Simon Fraser (smfr)]

Regressed at https://trac.webkit.org/changeset/268932/webkit

[Simon Fraser (smfr)]

I think this happens because we get to the end of a rendering update, but haven't cleared the Animations bit:

Page 0x3bc5f9680 renderingUpdateCompleted() - steps [] unfulfilled steps [Animations]

[Simon Fraser (smfr)]

The problem is that the layoutIfNeeded() at the end of a rendering update dirties the Animations and LayerFlush bits, so we trigger rendering updates on every frame.

te(this=0x000000018c5f9680, requestedSteps={ size = 1 }) at Page.cpp:1469:9
    frame #1: 0x00000001672d8df5 WebCore`WebCore::RenderLayerCompositor::scheduleRenderingUpdate(this=0x000000018c3e9720) at RenderLayerCompositor.cpp:574:12
    frame #2: 0x00000001672d4249 WebCore`WebCore::RenderLayerCompositor::notifyFlushRequired(this=0x000000018c3e9720, (null)=0x000000018c3ef780) at RenderLayerCompositor.cpp:567:5
    frame #3: 0x00000001672d421f WebCore`WebCore::RenderLayerBacking::notifyFlushRequired(this=0x000000018c34d870, layer=0x000000018c3ef780) at RenderLayerBacking.cpp:3747:18
    frame #4: 0x0000000166ccfea9 WebCore`WebCore::GraphicsLayerCA::noteLayerPropertyChanged(this=0x000000018c3ef780, flags=16, scheduleFlush=ScheduleFlush) at GraphicsLayerCA.cpp:4709:22
    frame #5: 0x0000000166cd13e9 WebCore`WebCore::GraphicsLayerCA::setTransform(this=0x000000018c3ef780, t=0x00007ffee5eeab80) at GraphicsLayerCA.cpp:675:5
    frame #6: 0x00000001672c2937 WebCore`WebCore::RenderLayerBacking::updateTransform(this=0x000000018c34d870, style=0x000000018cecf7b8) at RenderLayerBacking.cpp:647:26
    frame #7: 0x00000001672c7e3c WebCore`WebCore::RenderLayerBacking::updateGeometry(this=0x000000018c34d870, compositedAncestor=0x000000018c3e9850) at RenderLayerBacking.cpp:1278:5
    frame #8: 0x00000001672db448 WebCore`WebCore::RenderLayerCompositor::updateBackingAndHierarchy(this=0x000000018c3e9720, layer=0x000000018c3e9d10, childLayersOfEnclosingLayer={ size = 0, capacity = 0 }, traversalState=0x00007ffee5eebb58, scrollingTreeState=0x00007ffee5eebb78, updateLevel={ size = 0 }) at RenderLayerCompositor.cpp:1341:27
    frame #9: 0x00000001672db9a0 WebCore`WebCore::RenderLayerCompositor::updateBackingAndHierarchy(this=0x000000018c3e9720, layer=0x000000018c3e9be0, childLayersOfEnclosingLayer={ size = 0, capacity = 0 }, traversalState=0x00007ffee5eebda8, scrollingTreeState=0x00007ffee5eebdc8, updateLevel={ size = 0 }) at RenderLayerCompositor.cpp:1406:13
    frame #10: 0x00000001672db9a0 WebCore`WebCore::RenderLayerCompositor::updateBackingAndHierarchy(this=0x000000018c3e9720, layer=0x000000018c3e9850, childLayersOfEnclosingLayer={ size = 0, capacity = 0 }, traversalState=0x00007ffee5eebf50, scrollingTreeState=0x00007ffee5eebf98, updateLevel={ size = 0 }) at RenderLayerCompositor.cpp:1406:13
    frame #11: 0x00000001672d88fa WebCore`WebCore::RenderLayerCompositor::updateCompositingLayers(this=0x000000018c3e9720, updateType=AfterStyleChange, updateRoot=0x000000018c3e9850) at RenderLayerCompositor.cpp:916:9
    frame #12: 0x00000001672d7a7b WebCore`WebCore::RenderLayerCompositor::didRecalcStyleWithNoPendingLayout(this=0x000000018c3e9720) at RenderLayerCompositor.cpp:549:12
    frame #13: 0x000000016684d937 WebCore`WebCore::FrameView::updateCompositingLayersAfterStyleChange(this=0x000000018cecc010) at FrameView.cpp:810:39
    frame #14: 0x0000000165a3a6d9 WebCore`WebCore::Document::resolveStyle(this={ origin = file://, url = file:///Volumes/Data/Development/system/webkit/testcontent/animations/animation-api-two-fixed.html, inMainFrame = Detached, backForwardCacheState = NotInBackForwardCache }, type=Normal) at Document.cpp:2088:46
    frame #15: 0x0000000165a3b3c0 WebCore`WebCore::Document::updateStyleIfNeeded(this={ origin = file://, url = file:///Volumes/Data/Development/system/webkit/testcontent/animations/animation-api-two-fixed.html, inMainFrame = Detached, backForwardCacheState = NotInBackForwardCache }) at Document.cpp:2176:5
    frame #16: 0x000000016683d287 WebCore`WebCore::FrameView::updateLayoutAndStyleIfNeededRecursive(this=0x000000018cecc010) at FrameView.cpp:4445:43
    frame #17: 0x00000001668b72ae WebCore`WebCore::Page::layoutIfNeeded(this=0x000000018c5f9680) at Page.cpp:1463:15
  * frame #18: 0x00000001668b7ba5 WebCore`WebCore::Page::updateRendering(this=0x000000018c5f9680) at Page.cpp:1577:5


  * frame #0: 0x00000001668b73dc WebCore`WebCore::Page::scheduleRenderingUpdate(this=0x000000018c5f9680, requestedSteps={ size = 1 }) at Page.cpp:1469:9
    frame #1: 0x0000000165364be7 WebCore`WebCore::DocumentTimeline::scheduleAnimationResolution(this=0x000000018c37fae0) at DocumentTimeline.cpp:170:25
    frame #2: 0x0000000165368c15 WebCore`WebCore::DocumentTimeline::animationAcceleratedRunningStateDidChange(this=0x000000018c37fae0, animation=0x000000018cecf660) at DocumentTimeline.cpp:436:9
    frame #3: 0x0000000165376249 WebCore`WebCore::WebAnimation::acceleratedStateDidChange(this=0x000000018cecf660) at WebAnimation.cpp:1254:49
    frame #4: 0x0000000165376183 WebCore`WebCore::KeyframeEffect::addPendingAcceleratedAction(this=0x000000018c363840, action=TransformChange) at KeyframeEffect.cpp:1658:18
    frame #5: 0x00000001653763ee WebCore`WebCore::KeyframeEffect::transformRelatedPropertyDidChange(this=0x000000018c363840) at KeyframeEffect.cpp:1686:5
    frame #6: 0x0000000165378ad2 WebCore`WebCore::KeyframeEffectStack::applyKeyframeEffects(this=0x0000000195ec49a0, targetStyle=0x0000000195ebd660, previousLastStyleChangeEventStyle=0x0000000195ebd5a0, parentElementStyle=0x000000018cecdc58) at KeyframeEffectStack.cpp:145:21
    frame #7: 0x000000016762fe9c WebCore`WebCore::Styleable::applyKeyframeEffects(this=0x00007ffee5ee9d98, targetStyle=0x0000000195ebd660, previousLastStyleChangeEventStyle=0x0000000195ebd5a0, parentElementStyle=0x000000018cecdc58) const at Styleable.h:93:60
    frame #8: 0x000000016762e9c0 WebCore`WebCore::Style::TreeResolver::createAnimatedElementUpdate(newStyle=WebCore::RenderStyle @ 0x0000000195ebd540, styleable=0x00007ffee5ee9d98, parentChange=None, parentStyle=0x000000018cecdc58, parentBoxStyle=0x000000018cecdc58) at StyleTreeResolver.cpp:355:37
    frame #9: 0x000000016762e0aa WebCore`WebCore::Style::TreeResolver::resolveElement(this=0x00007ffee5eec7c0, element=0x000000018cecf3d0) at StyleTreeResolver.cpp:226:19
    frame #10: 0x0000000167630835 WebCore`WebCore::Style::TreeResolver::resolveComposedTree(this=0x00007ffee5eec7c0) at StyleTreeResolver.cpp:556:35
    frame #11: 0x0000000167631784 WebCore`WebCore::Style::TreeResolver::resolve(this=0x00007ffee5eec7c0) at StyleTreeResolver.cpp:619:5
    frame #12: 0x0000000165a3a5d4 WebCore`WebCore::Document::resolveStyle(this={ origin = file://, url = file:///Volumes/Data/Development/system/webkit/testcontent/animations/animation-api-two-fixed.html, inMainFrame = Detached, backForwardCacheState = NotInBackForwardCache }, type=Normal) at Document.cpp:2071:37
    frame #13: 0x0000000165a3b3c0 WebCore`WebCore::Document::updateStyleIfNeeded(this={ origin = file://, url = file:///Volumes/Data/Development/system/webkit/testcontent/animations/animation-api-two-fixed.html, inMainFrame = Detached, backForwardCacheState = NotInBackForwardCache }) at Document.cpp:2176:5
    frame #14: 0x000000016683d287 WebCore`WebCore::FrameView::updateLayoutAndStyleIfNeededRecursive(this=0x000000018cecc010) at FrameView.cpp:4445:43
    frame #15: 0x00000001668b72ae WebCore`WebCore::Page::layoutIfNeeded(this=0x000000018c5f9680) at Page.cpp:1463:15
    frame #16: 0x00000001668b7ba5 WebCore`WebCore::Page::updateRendering(this=0x000000018c5f9680) at Page.cpp:1577:5

[Simon Fraser (smfr)]

Interestingly, the bug goes away if I make a trivial change to the class attribute ("bubble ") or disable style sharing.

[Simon Fraser (smfr)]

Liam, does this affect any live web sites that you know of?

[Liam DeBeasi]

I discovered this issue while demoing Ionic's animation library benchmark website: https://flamboyant-brattain-9c21f4.netlify.app/

(Select "Ionic" and a bubble count and click "Start Test")

Other than the benchmark website, I am not aware of any other sites impacted by this.

[Antoine Quint]

Style sharing is disabled for elements with CSS Transitions or CSS Animations in SharingResolver::canShareStyleWithElement():

    if (style->transitions() || style->animations())
        return false;

This should likely check whether there are any keyframe effects for the candidate element.

[Antoine Quint]

Created attachment 443227 [details]
Patch

[Antti Koivisto]

Comment on attachment 443227 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=443227&action=review

> Source/WebCore/style/StyleSharingResolver.cpp:263
> -    if (style->transitions() || style->animations())
> +    if (candidateElement.hasKeyframeEffects(PseudoId::None))

Transitions are "keyframe effects" too?

[Antoine Quint]

(In reply to Antti Koivisto from comment #13)
> Comment on attachment 443227 [details]
> Patch
> 
> View in context:
> https://bugs.webkit.org/attachment.cgi?id=443227&action=review
> 
> > Source/WebCore/style/StyleSharingResolver.cpp:263
> > -    if (style->transitions() || style->animations())
> > +    if (candidateElement.hasKeyframeEffects(PseudoId::None))
> 
> Transitions are "keyframe effects" too?

Yes.

[Antoine Quint]

Committed r285256 (243867@main): <https://commits.webkit.org/243867@main>