** Changed in: mutter (Ubuntu Jammy)
Status: In Progress => Fix Committed
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https://bugs.launchpad.net/bugs/2030959
Title:
Cursor sometimes stutters after heavy shell animations in 42.9
Status in mutter package in Ubuntu:
Invalid
Status in mutter source package in Jammy:
Fix Committed
Bug description:
[ Impact ]
Cursor sometimes stutters after heavy shell animations in 42.9 if
there is no GUI animation in response to its movement. And it doesn't
stop stuttering until GUI redraws occur (giving the frame clock an
opportunity to measure lower GPU usage).
This is different to the recent bug fix that probably caused it:
Bug 2023766:
* only occurs when moving over animated GUIs.
* never recovers or corrects itself.
* was spatial jittering at full frame rate.
* reduced the frame rate of the GUI below it.
This bug:
* only occurs when moving over non-animated GUIs.
* does recover and correct itself.
* is stuttering at seemingly half frame rate, but perfect spatially.
* does not reduce the frame rate of the the GUI below.
I think the reason we only see this in 42 (jammy) is because that
predates the change in the triple buffering algorithm to scale based
on "dynamic max render time" alone.
[ Workaround ]
Add this to /etc/environment:
MUTTER_DEBUG_ENABLE_ATOMIC_KMS=0
and then reboot.
[ Test Plan ]
1. Stress GNOME Shell maximally by repeatedly entering/leaving the
overview and/or scrolling the app grid.
2. Stop suddenly and wiggle the mouse over some part of the desktop
that DOES NOT respond to mouse movement. Such as the wallpaper or some
blank grey space next to the app grid.
Expect: The mouse cursor does not get stuck in half frame rate.
[ Where problems could occur ]
In desktop frame timing since the clutter frame clock is being
changed. Although risk is minimal since we're just reverting to the
pre-July state of that code.
[ Other Info ]
The patch being dropped was found to not really be required in GNOME
42:
https://bugs.launchpad.net/ubuntu/+source/mutter/+bug/2023766/comments/13
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