https://bugs.kde.org/show_bug.cgi?id=459609
Bug ID: 459609
Summary: KWin switches the discrete GPU on every time a new
Wayland window is opened in a switchable graphics
setup
Classification: Plasma
Product: kwin
Version: 5.25.5
Platform: Archlinux
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: wayland-generic
Assignee: kwin-bugs-n...@kde.org
Reporter: putr...@gmail.com
Target Milestone: ---
SUMMARY
With dynamic switchable graphics set up on my system with Nouveau KWin appears
to poke the dGPU every time a native Wayland window is opened (including
Dolphin, System Settings, Konsole, KRunner and the logout/shutdown screen at
least), my laptop's dGPU light indicator turns on and there is a delay (about
2s) before the window appears. If the dGPU is already on and/or I force the
dGPU to stay off then there is no delay, and the issue does not occur with
XWayland windows (for example if I start Dolphin with `QT_QPA_PLATFORM=xcb`
set) nor with an X11 session. The dGPU does turn off again after a few seconds.
While I suspect the delay part could just be something specific to my system I
don't think KWin should even touch the dGPU unless said app is meant to use it
(as it would use battery power unnecessarily), and when I tried this same setup
with GNOME Wayland (I think it was with Fedora 34) it did not turn on the dGPU
when not required other than on startup.
STEPS TO REPRODUCE
1. Start a Plasma Wayland session
2. Wait until the dGPU turns off (say a minute or so)
3. Start a Wayland native app that does not use the dGPU (say Dolphin or
Konsole)
4. Close said app and reopen it
OBSERVED RESULT
There is a significant delay before the app window appears in step 4 instead of
being quick, and the dGPU turns on despite not being required.
EXPECTED RESULT
The app opens immediately in step 4.
SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.25.5
KDE Frameworks Version: 5.98.0
Qt Version: 5.15.6
Kernel Version: 5.19.9-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 8 × Intel® Core™ i7-6700HQ CPU @ 2.60GHz
Memory: 15.5 GiB of RAM
Graphics Processor: Mesa Intel® HD Graphics 530 (plus a GTX 960M as the dGPU)
Manufacturer: Micro-Star International Co., Ltd.
Product Name: GP62 6QF
System Version: REV:1.0
ADDITIONAL INFORMATION
In addition to the delay and the light indicator the file
`/sys/kernel/debug/vgaswitcheroo/switch` also says "DynPwr" instead of "DynOff"
for the dGPU when the issue occurs.
Also, I did not try the proprietary driver in this scenario since it does not
support power management for my old dGPU, plus I was not able to get any
Wayland native apps to use the dGPU without crashing in that case anyway (I
assume that could be a configuration error on my end).
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