Bug 400791

Summary:	Wrong reported refresh rate on 75hz monitor
Product:	[Plasma] kwin	Reporter:	tromzy
Component:	wayland-generic	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED LATER
Severity:	normal
Priority:	NOR
Version First Reported In:	unspecified
Target Milestone:	---
Platform:	Other
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description tromzy 2018-11-07 09:59:43 UTC

SUMMARY
On a Wayland session, I have a dual monitor setup : the laptop monitor is at 60hz and the external HDMI monitor is at 75hz. If I set the external monitor to 75hz in the Display KCM module, the OSD on my monitor reports 74.8 Hz which is good. But any application on the desktop reports 60 hz. Now, I have read that there were problems with XWayland reporting incorrect refresh rate values, but even native Wayland applications (Falkon, Retroarch) report 60hz.

STEPS TO REPRODUCE
1. Use a dual monitor setup with one monitor at 75hz
2. Try to set 75hz on the monitor
3. The desktop seems to be stuck at 60 hz / 60 FPS.

OBSERVED RESULT
The desktop seems to be stuck at 60 hz / 60 FPS.

EXPECTED RESULT
Applications should report 75hz instead of 60.

SOFTWARE VERSIONS
(available in About System)
KDE Plasma Version: 5.14.3
KDE Frameworks Version: 5.51.0
Qt Version: 5.11.2

ADDITIONAL INFORMATION
Archlinux, Intel Modesetting

Comment 1 Martin Flöser 2018-11-07 19:18:18 UTC

KWin does not have a per-screen render loop. Due to that the refresh rate of all screens is limited to the lowest refresh rate. So far what you experience is the expected behavior given KWin's internals.

I'm setting to RESOLVED/LATER as this is currently not a bug which we can fix, more like a new feature we need to implement. Once we have implemented a per screen rendering it will automatically resolve. Given that I think LATER makes most sense.