Secondary GPU frame rates are held back by dynamic-max-render-time

[Daniel van Vugt]

[ Impact ]

Secondary GPU frame rates are held back by dynamic-max-render-time as shown on this amdgpu setup connected to a 60 Hz monitor:

main: 30 FPS
main + CLUTTER_PAINT=disable-dynamic-max-render-time: 60 FPS

https://gitlab.gnome.org/GNOME/mutter/-/issues/3070

[ Test Plan ]

This is imprecise because many machines won't exhibit a measurable difference...

1. Set up a dual GPU machine with dual monitors using an open source driver such as amdgpu or nouveau. If you are using Mutter 46 or later then the closed source Nvidia driver may also be used in theory.

2. In a Wayland session, check that the frame rate being achieved on the monitor connected to the secondary GPU is at least that of the refresh rate.

3. Add CLUTTER_PAINT=disable-dynamic-max-render-time to /etc/environment and reboot.

4. In a Wayland session, check that the frame rate on the monitor connected to the secondary GPU has not changed (didn't get better) after the environment change.

5. Remove the change from /etc/environment.

[ Where problems could occur ]

Anywhere in frame scheduling and frame rate performance, since that is what changed.

[ Other Info ]