Games are choppy on XWayland

Affected version

• OS: ArchLinux (latest as of 2020.10.07)
• Mutter: 3.38.1
• Session: Wayland
• GPU / driver: AMD + mesa

Bug summary

Most native and wine games running through XWayland are choppy on a 144hz display, it feels like they are running at a lower frame rate. It is especially visible with Xonotic, but much less so with SuperTuxKart.

glxgears reports 144hz.

When launched with the SDL_VIDEODRIVER=wayland parameter, Xonotic is smooth.

Steps to reproduce

1. Start Xonotic or a Wine game (tested with Trackmania 2 Stadium on Steam and Trackmania 2020 on Lutris) in fullscreen mode.
2. Play the game, it feels choppy especially when moving fast.
3. Play the same games on a X11 session, they feel a lot smoother.

What happened

The games feel choppy.

The Xonotic in-game FPS counter reports 144fps when vsync is enabled in the game preferences, so the screen refresh rate is properly detected. But it feels like the game itself runs at a lower frame rate.

What did you expect to happen

The games should be as smooth as they are on a X11 session.

Additional information

It also used to happen with Mutter 3.36.6. I also tested Xonotic with a Fedora 33 beta LiveUSB, with the same results.