https://bugs.kde.org/show_bug.cgi?id=493745
Bug ID: 493745
Summary: kwin-wayland struggles with external GPUs
Classification: Plasma
Product: kwin
Version: 6.1.5
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: wayland-generic
Assignee: kwin-bugs-n...@kde.org
Reporter: khanich.opensou...@gmx.de
Target Milestone: ---
Sorry for the title, I am not sure what to name this.
SUMMARY
I have a laptop with an Intel iGPU (marked as default) and an AMD 6750XT as an
external GPU connected via Thunderbolt. The eGPU also has a display connected
via Display Port. Normally the Laptop lid is closed while using the external
monitor.
While trying to run a game fullscreen the eGPU gets used as expected (at least
according to radeontop), but I don't see a picture, just a black screen. When
opening the overview, I get a picture in that small window, but not an updating
one, more like a screenshot. The showed picture when leaving the overview again
is also that picture.
When I go and open the Laptop lid, the game gets automatically moved to the
internal monitor where it also runs as expected (but not as great as it could
be because of the limited bandwidth).
If I then go and open the overview again, drag the game to the external monitor
and then click on it, it's moved back to the internal monitor like KWin doesn't
want me to let the game run on that monitor.
If I start a game in windowed mode (I tested this with War Thunder with maximum
settings in the garage) I can move the window around freely. But the FPS
counter of the game shows something interesting: If the window is on the
external monitor, the FPS is at about 19 while on the internal monitor it's at
about 29.
None of this was a problem on Plasma version 6.0 (but I am not sure when it
changed because I didn't play anything for a few months).
My theory is that KWin for some reason really wants to move the window buffer
to the iGPU (or system RAM) and then struggles while moving it back because of
bandwidth limitation (after all, Thunderbolt 3 and 4 are practically PCIe 3.0
4x in bandwidth). usbtop gives about 200 kb/s "To Device" and about 28kb/s
"From Device" and watching a video on YouTube (at fullscreen Firefox) is giving
the same amount (although as I noticed YouTube does report about 1 dropped
frame per second).
SOFTWARE/OS VERSIONS
Linux-Kernel: 6.10.11-200.fc40.x86_64 (64-bit)
KDE Plasma Version: 6.1.5
KDE Frameworks Version: 6.6.0
Qt Version: 6.7.2
Linux distribution: Fedora Kinoite
ADDITIONAL INFORMATION
It's independent of the game and of if it's run via Wine/Proton or a native
game.
No, I didn't test in an Xorg session.
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