https://bugs.kde.org/show_bug.cgi?id=419387
Bug ID: 419387
Summary: Frame drops when the second monitor has 30Hz refresh
rate
Product: kwin
Version: 5.18.3
Platform: openSUSE RPMs
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: kwin-bugs-n...@kde.org
Reporter: i...@guoyunhe.me
Target Milestone: ---
SUMMARY
When you have two monitors with different refresh rates, the one higher refresh
rate drop frames (noticeably).
STEPS TO REPRODUCE
1. Connect to two 1080p monitors, we call them A and B
2. In KDE Settings, set refresh rates of both to 60Hz
3. Watch this video in monitor A https://www.youtube.com/watch?v=Cyxixzi2dgQ
4. In KDE Settings, set refresh rate of A to 60Hz and B to 30Hz
5. Watch the same video in monitor A
6. Shift+Alt+F12 to disable KWin composition
7. Watch the same video in monitor A
OBSERVED RESULT
When B is 60Hz, monitor A doesn't drop frames.
When B is 30Hz, monitor A drop frames noticeably.
When B is 30Hz but KWin composition is off, monitor A doesn't drop frames.
EXPECTED RESULT
Monitor A shouldn't drop frames when monitor B has a different refresh rate.
SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20200326
KDE Plasma Version: 5.18.3
KDE Frameworks Version: 5.68.0
Qt Version: 5.14.1
Kernel Version: 5.5.11-1-default
OS Type: 64-bit
Processors: 8 × Intel® Core™ i7-8550U CPU @ 1.80GHz
Memory: 31.1 GiB
ADDITIONAL INFORMATION
I think this is not deal to GPU performance limitation, because when you reduce
refresh rate of monitor B, the total computing load is smaller and GPU should
render faster.
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