Bug 99461 – Web Inspector: add timeline instrumentation for scrolling of a layer

• Component: Web Inspector (Deprecated)
• Status: RESOLVED FIXED

[Andrey Kosyakov]

Layer scrolling can be rather expensive -- for example, scrolling gmail with 100 conversations per page is ca. 6ms, which is currently not accounted by timeline.

[Andrey Kosyakov]

Created attachment 168931 [details]
Patch

[Pavel Feldman]

Comment on attachment 168931 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=168931&action=review

r- for didScroll vs didScrollLayer

> Source/WebCore/ChangeLog:8
> +        - added timeline instrumentation for scrolling of a layer;

What does it give to the user? Is there a way to address scrolling slowness?

> Source/WebCore/inspector/InspectorInstrumentation.h:147
> +    static void didScrollLayer(Frame*);

What is the difference with didScroll ?

> Source/WebCore/inspector/InspectorTimelineAgent.h:111
> +    void willScroll(Frame*);

Nit: we should come up with more dense way of instrumenting simple signals.

> Source/WebCore/rendering/RenderLayer.cpp:1712
> +    InspectorInstrumentation::willScrollLayer(frame);

Is there a TRACE_EVENT for this? Should we start with tracing it there and add it into the instrumentation if it proves to be valuable?

[Andrey Kosyakov]

(In reply to comment #2)
> (From update of attachment 168931 [details])
> View in context: https://bugs.webkit.org/attachment.cgi?id=168931&action=review
> 
> r- for didScroll vs didScrollLayer

> > Source/WebCore/ChangeLog:8
> > +        - added timeline instrumentation for scrolling of a layer;
> 
> What does it give to the user? 

It just closes the instrumentation gap -- we show where we spend considerable amount of time.

> Is there a way to address scrolling slowness?

There may be, but I imagine it's an effort of a different magnitude. I think there's still value in adding instrumentation for this first.

> > Source/WebCore/inspector/InspectorInstrumentation.h:147
> > +    static void didScrollLayer(Frame*);
> 
> What is the difference with didScroll ?

didScroll is for scrolling a view, while didScrollLayer is for scrolling a layer. The code paths appear to be somewhat different. It would be trivial to instrument both, but so far I failed to create a scenario where scrolling a view would be sufficiently slow, so the idea was to instrument only what we know to be slow.

> > Source/WebCore/inspector/InspectorTimelineAgent.h:111
> > +    void willScroll(Frame*);
> 
> Nit: we should come up with more dense way of instrumenting simple signals.

Totally agree. I do have some ideas for that, but I see this as a separate issue.

> > Source/WebCore/rendering/RenderLayer.cpp:1712
> > +    InspectorInstrumentation::willScrollLayer(frame);
> 
> Is there a TRACE_EVENT for this? Should we start with tracing it there and add it into the instrumentation if it proves to be valuable?

I did have it internally before adding inspector instrumentation. Will add to the patch as well.

[Andrey Kosyakov]

Created attachment 168955 [details]
Patch

[Pavel Feldman]

Comment on attachment 168955 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=168955&action=review

> LayoutTests/inspector/timeline/timeline-enum-stability-expected.txt:32
> +    Scroll : "Scroll"

ScrollLayer

[Andrey Kosyakov]

Committed r132088: <http://trac.webkit.org/changeset/132088>