[Webkit-unassigned] [Bug 257005] New: The first RemoteLayerTreeDrawingAreaProxy::commitLayerTree after being idle is always considered 'missed'.

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=257005

            Bug ID: 257005
           Summary: The first
                    RemoteLayerTreeDrawingAreaProxy::commitLayerTree after
                    being idle is always considered 'missed'.
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: mattwoodrow at apple.com
                CC: bfulgham at webkit.org, simon.fraser at apple.com,
                    zalan at apple.com

Each RemoteLayerTreeDrawingAreaProxy::commitLayerTree IPC messages results in a reply displayDidRefresh message being sent back to the WebProcess (once the display link fires) to trigger the next rendering update.

If the next commitLayerTree isn't received before the following display link callback, it goes into a 'missed commit' state, assuming the rendering update took more than one interval to render. In missed commit state, when the commitLayerTree eventually arrives, the displayDidRefresh reply is sent immediately, rather than waiting for the next display link callback.

This can't differentiate between a slow rendering update, and an idle WebContent process that decided it didn't need to do a rendering update at all. When we do resume from idle, we'll always be in missed commit state, and do a second rendering update (attempt) immediately, for no real benefit.

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