https://bugs.kde.org/show_bug.cgi?id=510113
Bug ID: 510113
Summary: Tearing fallback with adaptive sync breaks, resulting
in stuttering, at 240hz (RDNA4)
Classification: Plasma
Product: kwin
Version First 6.4.5
Reported In:
Platform: Arch Linux
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: wayland-generic
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
SUMMARY
When automatic adaptive sync and tearing are both enabled, legacy modesetting
is used, and the monitor is set to 240hz, pushing framerates above the
monitor's adaptive sync range causes stuttering instead of a graceful fallback
to tearing.
STEPS TO REPRODUCE
1. With atomic modesetting disabled, configure monitor to output in 240hz
(actually a fractional value, I can check when I get home, I think it was
239.76), with automatic adaptive sync and tearing enabled.
2. Run a Vulkan game in fullscreen that pushes a framerate that exceeds the
monitor's adaptive sync range. I used the enhanced Steam version of Quake
running at ~1600fps, but much lower framerates trigger the issue as long as
they exceed 240fps.
3. Move the mouse.
OBSERVED RESULT
Stuttery, visibly low-framerate gameplay and cursor movement and dropped frames
even when max frametime is very low.
EXPECTED RESULT
Smooth gameplay with tearing.
SOFTWARE/OS VERSIONS
Linux: 6.16.8-arch3-1
KDE Plasma Version: 6.4.5
KDE Frameworks Version: 6.18.0
Qt Version: 6.9.2
Mesa: 25.2.3-arch1.2
ADDITIONAL INFORMATION
CPU: Ryzen 7 5800XT
GPU: Radeon RX 9060XT 16GB
Output connector: DisplayPort
Environment Variables: KWIN_DRM_NO_AMS=1
The game in question uses Xwayland.
Removing any of the offending variables independently fixes the issue. Lowering
the refresh rate to 144hz or disabling adaptive sync both fix the issue and
tears, and disallowing tearing removes the stutter but is suboptimal for use
case.
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