https://bugs.kde.org/show_bug.cgi?id=509020
Bug ID: 509020
Summary: KWin Wayland insufficient performance for video
playback vs. Xorg on slow Gemini Lake GPU
Classification: Plasma
Product: kwin
Version First 6.4.4
Reported In:
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: wayland-generic
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
SUMMARY
On a slow notebook with Intel Gen 9.5 Gemini Lake graphics, video playback in
mpv stutters vs. Xorg uncomposited.
STEPS TO REPRODUCE
1. Use mpv (ideally recent git-master build, including recent libplacebo
git-master) to play a 1080p 24fps video on a 1080p 48Hz display with this basic
mpv config:
vo=gpu-next
hwdec=vaapi
gpu-api=opengl
sigmoid-upscaling=no
linear-downscaling=no
correct-downscaling=no
cscale=bilinear
scale=bilinear
dscale=bilinear
video-sync=display-resample
2.
Judge playback result or enable mpv stats overlay with shift + i
OBSERVED RESULT
On Wayland, playback stutters and mpv reports mistimed/delayed frames in its
stats.
EXPECTED RESULT
It shouldn't stutter. On uncomposited Xorg fullscreen, playback is without
stutter and without tearing. Also on Windows, mpv D3D11 can play such videos
with the provided config on the same device without stutter, also in windowed
mode.
This used to work also on KWin Wayland, back in the Plasma 5 days with manually
configured maximum compositor latency. It shouldn't be related to thermal or
power throttling, as power draw during video playback is just 3.5 Watts.
Can test env vars and also patches that work against the stable KWin build, or
soon 6.5 beta.
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch kernel 6.16.4
KDE Plasma Version: 6.4.4
KDE Frameworks Version: 6.17.0
Qt Version: 6.9.2
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