https://bugs.kde.org/show_bug.cgi?id=463963
Bug ID: 463963
Summary: Reverse PRIME on Wayland causes lower (matched) FPS on
nvidia 525.78.01.
Classification: Plasma
Product: kwin
Version: 5.26.5
Platform: Archlinux
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: multi-screen
Assignee: kwin-bugs-n...@kde.org
Reporter: g...@silikeite.me
Target Milestone: ---
SUMMARY
Prior to nvidia 525.78.01, Reverse PRIME was unusable due to pinning one of the
CPU cores to 100% with a low FPS (~30FPS on my setup), however this low FPS
applies only to the external display. This is clearly not a multi-monitor issue
with FPS mismatch on the screens, since my non-Reverse PRIME output can drive
both screens (144FPS main and 75FPS external) at their respective max FPS.
The new nvidia version fixed the CPU usage problem, and there are no hiccups on
X11. However, on Wayland, both screens now get driven to a lower FPS (~50FPS)
in my case, although without the CPU usage issue. The non-Reverse PRIME
multi-monitor setup still works fine (albeit with the screen occasionally going
black when my fridge compressor turns on, which doesn't happen with the nvidia
output).
STEPS TO REPRODUCE
1. Boot to Wayland session on an Nvidia/Intel Optimus laptop. Use kwin 5.26.5
and nvidia 525.78.01
2. Use Reverse PRIME on a monitor with lower FPS than the main display, or set
the monitor to use a lower FPS than the main display.
3. Open testufo.com on both screens. If your eyes are sharp, observe the
smoothness/jumpiness of the cursor.
4. Connect the monitor to a non-Reverse PRIME port (might not be possible on
some laptops) and open testufo.com on both screens again.
OBSERVED RESULT
Both displays output the same FPS that is lower than the maximum FPS on either
monitor when using reverse PRIME.
EXPECTED RESULT
The system should be able to drive each monitor at their respective maximum FPS
when no GPU intensive actions are being done, just like with my non-Reverse
PRIME port.
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: linux-zen 6.1.3-zen1-1-zen
KDE Plasma Version: 5.26.5
KDE Frameworks Version: 5.101.0
Qt Version: 5.15.7
ADDITIONAL INFORMATION
I can live with using the DP port on my laptop, although my DP-over-USB C port
is Reverse PRIME, which I want to use as it is more convenient.
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