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I have screen tearing issues. When I set Tearing prevention ("vsync") in Compositor to something else and then back to Automatic the screen tearing is gone. I would like to know what configuration files Tearing prevention ("vsync") changes to troubleshoot this problem and find a permanent fix.

I test for screen tearing with this video.

I also have screen tearing with the latest live iso with both free and non-free drivers.

Operating System: Manjaro Linux 
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.70.0
Qt Version: 5.15.0
Kernel Version: 5.6.16-1-MANJARO
OS Type: 64-bit
Processors: 8 × Intel® Core™ i7-6700HQ CPU @ 2.60GHz
Memory: 15,5 GiB of RAM
GPU: Nvidia GeForce 940M
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I think that option is helpful only if you don't have VSync feature in your native gpu drivers settings.

If you are using nouveau or some other drivers, set this option to automatic. If you are using Nvidia drivers for your Nvidia card, then you can disable this option & set it to "never".

Because you already will be having Force Composition Pipeline in Nvidia settings.

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WARNING : This question obviously relates to kwin versions < 5.21. Things have considerably changed since and the whole vsync strategy was rewritten. Therefore, if that problem reoccurs with >=5.21 versions, the following answer should be considered obsolete.

As far as I can tell from my own experience :

I second MPK99's suggestion for :

Vsync : Never (as part of kde systemsettings) + Sync to VBlank as part as NVIdia proprietary drivers settings. Which, in my case, gracefully fits 99 % of the purpose.

However, I can still observe tearing with HD videos played back fullscreen by VLC.

I was able to solve this problem using to different means :

  • Option "MetaModes" "nvidia-auto-select +0+0 {ForceFullCompositionPipeline=On}" As part of xorg.conf, exclusive or :
  • vsync = Automatic or Only when Cheap as part of kde settings.

I stayed with the latter because of a significant less amount of (local)timers interrupts needed.

So, in order to answer your question : "What does KDE compositor...", for me, it enables tearing-free full screen HD video rendering in VLC at a less cost (in terms of interrupts => context switches) than any other method.

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