Ubuntu
mutter package

  1. Noble (24.04)
  2. Bug #2070438
  3. Comment #0

Comment 0 for bug 2070438

Revision history for this message
Daniel van Vugt (vanvugt) wrote :

[ Impact ]

Fullscreen direct scanout is not used if you enable the hidden experimental VRR feature in Mutter 46.

[ Test Plan ]

0. Find a monitor that is VRR capable.
1. Set MUTTER_DEBUG=kms in /etc/environment
2. Enable VRR (TODO: need to relearn all the steps required)
3. Reboot.
4. Log into a Wayland session.
5. Open Google Chrome, start an animation like https://www.vsynctester.com/ and make it full screen (F11).
6. journalctl -f /usr/bin/gnome-shell | grep Post
7. Verify the "Post" messages you see mention direct scan out and not "composite".

[ Where problems could occur ]

Since the fix affects the runtime decision of whether to allow triple buffering or stay double buffering, the main risk is that triple buffering wouldn't be used in some situation where we would rather have it to maintain a smoother frame rate.

[ Other Info ]

First reported upstream in:
https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1441#note_2062222

We DO NOT recommend enabling the VRR feature anyway because it is still buggy:
https://gitlab.gnome.org/GNOME/mutter/-/issues/3419