Comment # 6 on bug 1086640 from Max Staudt

Hi Peter,

Since the upstream bug keeps referring people to the compositor, I've searched
around for possible causes, and found a hint here:

  https://bugs.kde.org/show_bug.cgi?id=363093

First of all, please make sure that KWin's compositing is enabled, and that in
the "Compositor" settins (right next to the display settings), "Tearing
prevention ("vsync")" is actually enabled - if in doubt, try the setting "Full
screen repaints".

If you go to the KDE settings > Displays, you can select a "Primary display".
Can you experiment with different settings here? Setting the external 4K
monitor that I've hooked up to the T450 here as primary helps a lot, at least
on the external display. The reason behind this is that a generic hardware
interface can only really sync to a single monitor, AFAIK.

Note on the radeon driver, which as mentioned in the upstream bug in Comment 1,
has a TearFree option per output: That may be a hardware specific option, which
the generic modesetting driver may never be able to implement.