https://bugs.kde.org/show_bug.cgi?id=452219
Bug ID: 452219
Summary: Low fps and high CPU usage on external monitor
connected to NVIDIA when default GPU is Intel
Product: kwin
Version: 5.24.4
Platform: Archlinux Packages
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: wayland-generic
Assignee: kwin-bugs-n...@kde.org
Reporter: ye.jingc...@gmail.com
Target Milestone: ---
SUMMARY
My laptop is an Intel+NVIDIA optimus one, which has an HDMI port on Intel GPU,
and an mini DisplayPort on NVIDIA.
If the external monitor is connected to the NVIDIA miniDP port, though both
internal and external monitor are detected correctly and both show the desktop,
whole desktop renders pretty low fps, and kwin_wayland process consumes nearly
100% CPU of a single core. However, if the image on external monitor stays
static, kwin_wayland stays calm and the internal monitor is smooth as usual.
If I set environment variable `KWIN_DRM_DEVICES=/dev/dri/card0` (NVIDIA GPU
determined from /dev/dri/by-path and lspci), kwin can drive the external
monitor even if connected to NVIDIA miniDP port, but the internal monitor is
not detected. Moreover, if I set
`KWIN_DRM_DEVICES=/dev/dri/card0:/dev/dri/card1` (NVIDIA followed by Intel),
same syndrome occurs just like when KWIN_DRM_DEVICES is absent.
STEPS TO REPRODUCE
1. Boot into KDE desktop without external monitor
2. Connect external monitor to NVIDIA GPU
3. Logout and set KWIN_DRM_DEVICES=/dev/dri/card0 in /etc/environment (from tty
or ssh)
4. Login again with the external monitor still on NVIDIA GPU
OBSERVED RESULT
After step 2, both monitor works, but desktop is low fps and kwin_wayland
process consumes high CPU usage;
after stop 4, desktop on external monitor works smoothly, but internal monitor
is not detected.
EXPECTED RESULT
No matter which GPU is default, or which port external monitors connect to,
desktop should be smooth.
SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.24.4
KDE Frameworks Version: 5.92.0
Qt Version: 5.15.3
Kernel Version: 5.17.1-zen1-1-zen (64-bit)
Graphics Platform: Wayland
Processors: 8 × Intel® Core™ i7-6700HQ CPU @ 2.60GHz
Memory: 15.5 GiB of RAM
Graphics Processor: NVIDIA GeForce GTX 965M/PCIe/SSE2
Graphics Processor: Intel HD Graphics 530
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