https://bugs.kde.org/show_bug.cgi?id=468251
Bug ID: 468251
Summary: After updating to 5.27.4 changing the display refresh
rate on Wayland no longer works properly
Classification: Plasma
Product: kwin
Version: 5.27.4
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
While my laptop's display supports 144Hz refresh rate I perfer keeping it at
60Hz instead since I don't think the minor smoothness advantage is worth the
extra load on the system, plus it would also add unnecessary power draw on
battery.
Unfortunately, after upgrading to 5.27.4 I noticed that things looked strangely
smooth despite having set the refresh rate at 60Hz, then I found out that KWin
was still rendering at 144 fps (based on the Show FPS effect), and Firefox with
a vsync tester website also reports running at 144 fps instead of 60 fps.
Changing the refresh rate (both via System Settings and kscreen-doctor) also
only caused the screen to flash once very quickly (normally changing refresh
rates takes a whole second or two), and all that did was change the "Maximum
FPS" value in the Show FPS effect, while the "current FPS" part still says 144
the whole time.
I believe the culprit is this commit:
https://invent.kde.org/plasma/kwin/-/commit/dc95392b982ac9ae95a72e5f38e5ecc499f0bc19
(backends/drm: restrict common mode generation to drivers that support
scaling), if I compile KWin 5.27.3 with that patch I also see this bug, while
plain KWin 5.27.3 works fine.
STEPS TO REPRODUCE
1. Have a screen that supports 60 and 144 Hz
2. Set the refresh rate to 60 Hz in a Wayland session
3. Enable the "Show FPS" effect
OBSERVED RESULT
While the maximum FPS value is 60 the current FPS value is still 144.
EXPECTED RESULT
The maximum and current FPS values both drop to 60.
SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.27.4
KDE Frameworks Version: 5.104.0
Qt Version: 5.15.8
Kernel Version: 6.2.8-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 6800H with Radeon Graphics
Memory: 14.9 GiB of RAM
Graphics Processor: AMD Radeon Graphics
Manufacturer: HP
Product Name: OMEN by HP Gaming Laptop 16-n0xxx
ADDITIONAL INFORMATION
After logging into a Wayland session if I switch back to X11 the bug persists,
changing the refresh rate via xrandr also has no real effect, but if I reboot
and log into an X11 session first then changing refresh rates work as before.
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