[Webkit-unassigned] [Bug 234303] Varying rAF during WebGL video upload on iPod touch 7, iOS 15.2

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=234303

--- Comment #9 from Simon Taylor <simontaylor1 at ntlworld.com> ---
Here's an even simpler reproducer which doesn't actually do anything other than busy-loop for 8ms in its rAF callback:
https://tango-bravo.net/webkit-bug-234303/raf_busyloop.html

Could it perhaps have something to do with content process isolation, when switching back to an existing content process from another domain? (I don't even know if WebKit does that but know it's a thing in Chrome)

This appears to be the behaviour, 100% reproducible from a clean start (Safari killed, no tabs open, even cleared all data and rebooted first but this isn't necessary):

1) Visit this bugzilla page
2) Click any of the links to any of the demos on this page
3) Note rAF loop runs at 60 FPS
4) Back to this page
5) Click any other link to the same domain (doesn't need to be the same page)
6) Note rAF now runs at <60 FPS. <60FPS persists through refresh, background / foreground app switch, history navigation.
7) Kill Safari (still with tab open) and re-open. Back to 60 FPS.

Copying/pasting the URL from a <60FPS tab into a new one also gets 60FPS, so seems something to do with the Tab & Domain combo that is affected.

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