Bug 498628 - Framerate Doubling in Bursts when mirroring screens
Summary: Framerate Doubling in Bursts when mirroring screens
Status: CONFIRMED
Alias: None
Product: kwin
Classification: Plasma
Component: multi-screen (show other bugs)
Version: 6.2.5
Platform: Arch Linux Linux
: NOR normal
Target Milestone: ---
Assignee: KWin default assignee
URL:
Keywords: multiscreen
Depends on:
Blocks:
 
Reported: 2025-01-13 22:16 UTC by Jake
Modified: 2025-01-14 17:54 UTC (History)
3 users (show)

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Description Jake 2025-01-13 22:16:28 UTC 
SUMMARY
KDE will double the framerate of mirrored high refresh rate screens in bursts, this will create stuttering and smoothness issues



STEPS TO REPRODUCE
1. Set two monitors to a high refresh rate
2. Mirror the two monitors using Display configuration


OBSERVED RESULT
Frame rate will frequently swap between desired frame rate and the combined frame rates of the two screens.


EXPECTED RESULT
Both screens stay at the maximum framerate set in Display configuration

SOFTWARE/OS VERSIONS
Linux/KDE Plasma:  Arch 6.12.8
KDE Plasma Version: 6.2.5
KDE Frameworks Version: 6.9.0
Qt Version: 6.8.1

ADDITIONAL INFORMATION
Video of the effect here:
https://imgur.com/a/T6HzVD6
along with screenshot of monitor settings
Comment 1 Zamundaaa 2025-01-13 23:28:39 UTC 
I'm not sure why this would come in bursts, but the issue is likely that we send frame callbacks for every time KWin renders the window, on any output. If we restrict that to only send frame callbacks for one output, then the problem should go away.