https://bugs.kde.org/show_bug.cgi?id=485927
[email protected] changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |[email protected] --- Comment #52 from [email protected] --- So, there are actually 2 bugs at play here that have very similar (and possibly related) symptoms and both of them are happening on Wayland. I realized this yesterday because I'm experiencing this Qt bug in a laptop with a 120 Hz built-in screen that's connected to a 144 Hz external monitor. Turns out, yes, Qt indeed has a timer bug because I have the exact same symptoms described on Comment 2, with all Plasma animations looking super choppy in the external monitor (dragging windows around, maximizing, minimizing, etc), with the notable exceptions of the Emoji Picker, System Monitor, and Discover being super smooth. This doesn't happen in the built-in screen, where everything is smooth regardless. This particular laptop has an Optimus setup (dual Intel Graphics/NVIDIA GPU), and there seems to be an NVIDIA bug that has a lot of things in common with this Qt bug. This is, however, not exclusively affecting NVIDIA, as some of the people in this comment section have AMD Radeon graphics. On the NVIDIA side at least, it seems that something (this Qt bug?) is causing a delay in per-frame notification between the compositor and the GPU, causing the NVIDIA card to miss the vblank interval every other frame, leading to a halved refresh rate (more info here: https://github.com/NVIDIA/open-gpu-kernel-modules/issues/650#issuecomment-2668160546). This problem affects both the NVIDIA open and proprietary drivers. I could actually verify this being the case for this particular laptop, because the Blur Busters UFO test would actually show 70-72 FPS on the external monitor indicating that the refresh rate of Plasma desktop was exactly half of the 144 Hz of the external monitor. Moving the browser window into the built-in display would cause the UFO test to immediately jump to 117-120 FPS, matching the 120 Hz of the built-in screen. At the very least, on the NVIDIA side, this is a widespread bug that not only affects Kwin, but other Wayland compositors as well (see: https://forums.developer.nvidia.com/t/nvidia-please-get-it-together-with-external-monitors-on-wayland/301684). I haven't tested this on AMD, because I don't have any laptops that have a Radeon dGPU, and my desktop PC isn't affected by this bug. However, a workaround for the time being is forcing Kwin to change GPU priority by editing /etc/environment and use the KWIN_DRM_DEVICES environment variable to force dGPU preference (I personally set it to "/dev/dri/by-path/pci-0000\:01\:00.0-card:/dev/dri/by-path/pci-0000\:00\:02.0-card"). This solves the framerate issue on the external monitor by forcing the dGPU to draw the Plasma desktop, but it's not ideal because of the high power consumption when on battery. This probably also helps with AMD GPUs, but someone else would have to test it. Still, like I said, this is only a workaround for the time being, and should not be used as a final solution. -- You are receiving this mail because: You are watching all bug changes.
