https://bugs.kde.org/show_bug.cgi?id=487670
Bug ID: 487670
Summary: Mouse cursor is dropping/skipping frames with explicit
sync driver
Classification: Plasma
Product: kwin
Version: git-stable-Plasma/6.1
Platform: Arch Linux
OS: Linux
Status: REPORTED
Severity: major
Priority: NOR
Component: wayland-generic
Assignee: kwin-bugs-n...@kde.org
Reporter: f...@fellr.net
Target Milestone: ---
There are a lot of synchronisation issues being discussed right now, but I
think I have singled this one out.
STEPS TO REPRODUCE:
1. Aquire a system with an NVIDIA GPU (RTX 2080 Ti in this case)
2. Aquire a high refresh rate monitor, like 144 Hz (may be optional)
2. Install the beta driver version 555.42.02
3. Install Plasma 6.1 beta with KWin 6.0.90
4. Set System Settings → Display & Monitor → Adaptive sync to `Never` in order
to filter out possible issues with adaptive sync.
5. Set `KWIN_DRM_DISABLE_TRIPLE_BUFFERING=1` in order to filter out possible
side effects with triple buffering.
6. Use the computer. Open windows, move windows, close windows, and pay
attention to the mouse cursor movement. It takes a bit of a trained eye.
OBSERVED RESULT:
7. Observe the following behavior(s) of the mouse cursor:
- Skipping frames: The mouse cursor jumps over short distances.
- Frame rate drops: The mouse cursor appears to be rendered at a lower frame
rate for short (~1 second) periods.
NOTE:
This behavior is also observable in the 6.0.5 branch with explicit sync:
https://invent.kde.org/plasma/kwin/-/commits/work/zamundaaa/cherry-pick-explicit-sync
EXPECTED RESULT
The mouse cursor movement should be rendered smoothly at all times, just like
in Plasma 6.0 without explicit sync.
SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 6.0.90
KDE Frameworks Version: 6.2.0
Qt Version: 6.7.1
Kernel Version: 6.9.2-zen1-1.1-zen (64-bit)
Graphics Platform: Wayland
Processors: 24 × AMD Ryzen 9 3900X 12-Core Processor
Memory: 31.3 GiB of RAM
Graphics Processor: NVIDIA GeForce RTX 2080 Ti/PCIe/SSE2
ADDITIONAL INFORMATION
NVIDIA Driver Version: 555.42.02
ENVIRONMENT:
# Native KDE dialogs in Firefox
GTK_USE_PORTAL=1
# Wayland support in Thunderbird
MOZ_ENABLE_WAYLAND=1
# Get other things to use Wayland
SDL_VIDEODRIVER=wayland,x11
QT_QPA_PLATFORM=wayland
ELECTRON_OZONE_PLATFORM_HINT=auto
CLUTTER_BACKEND=wayland
# Maybe fix KDE stutter?
KWIN_DRM_DISABLE_TRIPLE_BUFFERING=1
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