https://bugs.kde.org/show_bug.cgi?id=489069
Bug ID: 489069
Summary: Choppy VRR/Adaptive Sync on Wayland
Classification: Plasma
Product: kwin
Version: 6.1.0
Platform: Fedora RPMs
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: performance
Assignee: kwin-bugs-n...@kde.org
Reporter: kyri...@proton.me
Target Milestone: ---
SUMMARY
So here's my setup : I run Fedora 40 with KDE Plasma 6.1 on a dual GPU system
(Radeon WX 2100 and RX 6900 XT) on Wayland, using PRIME GPU Offloading (so I
can passthrough the 6900 XT for VMs).
It works fine, however VRR is very choppy, almost as if it is switching between
two framerates (Low Framerate Compensation kicking in ?). Taking a look at the
monitor OSD indicates that the framerate is all over the place, bouncing in the
VRR range.
What I tried :
Delaying cursor updates with KWIN_DRM_DELAY_VRR_CURSOR_UPDATES=1 and disabling
HW cursor with KWIN_FORCE_SW_CURSOR=1 => doesn't change anything, is apparently
the default behavior on KDE 6.1
Disabling Atomic Modesetting with KWIN_DRM_NO_AMS=1 and delaying cursor updates
with KWIN_DRM_DELAY_VRR_CURSOR_UPDATES=1 and use HW cursor with
KWIN_DRM_DONT_FORCE_AMD_SW_CURSOR=1 => the issue somewhat remains but it is
smoother, but with visible tearing happening where it should not be the case
Changing the GPUs power profiles : doesn't do much
Using only the bigger GPU : also broken
Disabling Triple Buffering with KWIN_DRM_DISABLE_TRIPLE_BUFFERING=1 : also
broken
Using KDE 5.27.10 : works fine, but breaks after like 80 FPS
STEPS TO REPRODUCE
1. Enable Adaptive Sync
2. Launch a fullscreen app (i.e. Nixola's VRRTest) and observe the framerate
fluctuations on the monitor's OSD
OBSERVED RESULT
Choppy/stuttery image, with refresh rate bouncing in the VRR range and
sometimes hitting the monitor's refresh rate
EXPECTED RESULT
Smooth image, with monitor's refresh rate following the app's refresh rate
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Fedora 40/KDE Plasma 6.1.0
(available in About System)
KDE Plasma Version: 6.1.0
KDE Frameworks Version: 6.3.0
Qt Version: 6.7.1
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