From discussion with Alexandre the profile was taken when he wasn't actively interacting with the browser, so there's an expectation that we shouldn't be rendering continuously, however the profile shows that awe are. There's some activity on the parent main threads as well as content processes at various times, but I also see parts where all main threads are idle and we keep rendering. According to profile markers, a lot of the frames don't have draw calls nor invalidated picture cache times, so we appear to be continuously compositing only.
Bug 1733377 Comment 1 Edit History
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From discussion with Alexandre the profile was taken when he wasn't actively interacting with the browser, so there's an expectation that we shouldn't be rendering continuously, however the profile shows that awe are. There's some activity on the parent main threads as well as content processes at various times, but I also see parts where all main threads are idle and we keep rendering. According to profile markers, a lot of the frames don't have draw calls nor invalidated picture cache tiles, so we appear to be continuously compositing only.