[raspi] GNOME Shell 44.0 runs at 30 FPS unless the CPU is being stressed

This bug has been reported on the Ubuntu ISO testing tracker.

A list of all reports related to this bug can be found here:
https://iso.qa.ubuntu.com/qatracker/reports/bugs/2017097

How do you determine shell fps?

To get FPS in the system journal set environment:

  CLUTTER_SHOW_FPS=1

which will give you accurate FPS but not accurate render times because OpenGL is asynchronous. To get accurate render times too you will need to slow it down a little by adding:

  COGL_DEBUG=sync-frame

Think I found it. The new version of triple buffering in mutter 44.0 is too aggressive at scaling back to double buffering. So that's why 22.04 and 22.10 felt faster on Pi than 23.04 does right now.

The workaround is to add this to /etc/environment:

  MUTTER_DEBUG_TRIPLE_BUFFERING=always

See also bug 2017137

Fix committed to https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1441 but I am waiting till there is a 44.1 tag before rebasing, branching, and proposing a new triple buffering patch to salsa. I will also be away till Monday so it probably won't happen before then.

Fixed in mutter 44.1 which is now in Ubuntu 23.10

Hello Daniel, or anyone else affected,

Accepted mutter into lunar-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/mutter/44.1-0ubuntu1 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-lunar to verification-done-lunar. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-lunar. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

Verified fixed (on Raspberry Pi 400) using mutter 44.1-0ubuntu1

Also verified on a Pi 4 (mutter 44.1-0ubuntu1); video playback is smooth again!

This bug was fixed in the package mutter - 44.1-0ubuntu1

---------------
mutter (44.1-0ubuntu1) lunar; urgency=medium

  [ Jeremy Bícha ]
  * New upstream release (LP: #2020225, LP: #2012717, LP: #2013216,
    LP: #2015861, LP: #2017097)
  * debian/libmutter-12-0.symbols: Add new symbols
  * Drop 3 patches applied in new release

  [ Daniel van Vugt ]
  * Update triple buffering patch for Mutter 44.1 (LP: #2017137)

 -- Jeremy Bícha <email address hidden> Fri, 19 May 2023 16:18:13 -0400

The verification of the Stable Release Update for mutter has completed successfully and the package is now being released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.