KWin Wayland: Halved / poor frame pacing on external monitor (dGPU output) in hybrid Intel+NVIDIA setup

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Hello everyone,

I’m experiencing a frustrating frame pacing issue on KDE Plasma Wayland with a hybrid GPU laptop.

Hardware:

  • Lenovo ThinkPad P16 Gen 2

  • Intel iGPU (drives internal 60 Hz display)

  • NVIDIA RTX 2000 Ada (8 GB) — HDMI port is hardwired to this dGPU

  • External monitor capable of 120 Hz

The Problem:
When using a Plasma Wayland session (KWin defaults to iGPU for compositing):

  • The cursor on the external monitor is smooth.

  • Moving windows, browsers, or any content stutters badly.

  • UFO Test (testufo.com) shows drops down to ~49 FPS at 120 Hz.

  • Internal laptop screen remains at 60 Hz.

  • External display refresh rate is halved (from 120Hz to 60Hz).

This matches the classic hybrid setup symptom where the iGPU has to copy/compose frames to the dGPU output, causing timing issues.

What I’ve tried:

  • Setting the external monitor to 120 Hz (native).

  • The only effective workaround is forcing KWin to use the dGPU with KWIN_DRM_DEVICES (dGPU first). This gives full smoothness but is not ideal as it runs everything on the 8 GB NVIDIA card, quickly consuming VRAM and increasing power/heat.

Note: I had this issue on GNOME as well, but it seems that it was fixed with the release of GNOME 50 (they also mention this in their release notes) However i prefer to not use GNOME. I’m also sure this issue is independent of the distro.

Questions:

  1. Are there better environment variables or config options I should test (related to DMA fences or triple buffering)?

  2. Would logs or specific outputs help?

Thanks in advance! This is one of the last major pain points keeping me from using Plasma on Wayland.