Xorg sessions have higher output lag than Wayland sessions [performance]
Xorg sessions have higher output lag than Wayland sessions.
Grab a window with the mouse and drag it around smoothly.
Expected: the same minimal gap between the cursor and the window's title bar in both Xorg and Wayland sessions.
Observed: a bigger gap (higher latency) in Xorg sessions.
I only realized this was a bug when I stumbled on a fix while experimenting with the presentation timing logic in mutter. So the issue is related to pre-rendering too many frames, and filling the triple/quad buffer queue when really we would only like to be double buffered.
Downstream bug: https://bugs.launchpad.net/bugs/1796549