GNOME Lands Nice Optimization For Wayland Gaming

Merged this week into the GNOME Mutter compositor codebase is what should be a beneficial optimization for those enjoying Linux gaming under the GNOME Wayland session.

The change made to Mutter is around no longer blocking in glGetQueryObjecti64v when engaging in direct scanout purposes such as for full-screen games.

This in turn reduces or eliminates stuttering and missed frames, improves frame pacing, stabilizes frame timing, and also provides a better variable rate refresh (VRR / FreeSync) experience with AMD graphics processors.

The MR by Dor Askayo sums it up as:

"This MR assumes that the Wayland transaction mechanism results in zero buffer rendering time before presentation in the direct scanout case, and thus removes the need to query for GPU timestamps using glGetQueryObjecti64v.

See commit messages for more information.

It works quite well from initial testing; fixes dynamic max rendering time estimations, reduces stutter/missed frames, improves frame pacing and stabilizes frame timings. This is also required for smooth VRR experience with AMD GPUs."

This also eliminates nearly 200 lines of code and simplifies the logic for the Wayland direct scanout code path.

This improvement was motivated by this two month old bug report by Ernst Sjöstrand around experiencing irregular FPS under the GNOME Wayland session. Ultimately this change should be a very nice improvement for those running full-screen games under the GNOME Wayland session.