https://bugs.kde.org/show_bug.cgi?id=525619

--- Comment #26 from Conn O'Griofa <[email protected]> ---
Testing together against master with fixed rate (60/1) negotiated:
https://invent.kde.org/plasma/kwin/-/merge_requests/9082
https://invent.kde.org/plasma/kwin/-/merge_requests/9948
https://invent.kde.org/plasma/kwin/-/merge_requests/9956

Unfortunately this is still exhibiting random screencast frame dips.

The behaviour is definitely better than master, and the specific 60 -> 30 -> 60
manual toggle testcase with Resident Evil Requiem is not immediately possible
to trigger any more, but normal gameplay triggers random screencast incoming
rate collapse that seems related to 1% lows.

A reliable reproducer on my system is seen in the game Pragmata at 60FPS with
vsync enabled. When in the main hub you can select skins for the characters,
and scrolling the list causes the skin previews to load in immediately, which
happens to trigger some very brief framerate fluctuations on my system. The
problem related to the screencast is that when there's a 1% low that falls
below the vblank period, the screencast will (naturally) follow that dip, but
subsequent incoming screencast framerate collapses to 30-40fps for several
seconds to tens of seconds beyond the point where the in-game framerate had
already recovered and stabilized to a smooth ~16.7ms frametime as seen in
mangohud.

I'll try to find a better test case that doesn't rely on specific games, but
I'm struggling to find a clean reproducer with open source/free software. For
example, I tried vrrtest with vsync on and toggling random stutter of 33ms, but
it doesn't seem to cause screencast collapse that lingers past the actual host
framerate recovering in the same way as seen in games.

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