I tried fedora rawhide too - same problem, so this seems to be a problem of some Plasma component, not Qt 6.7

Does it happen on both X11 and Wayland, or only one?

(In reply to Nate Graham from comment #2)
> Does it happen on both X11 and Wayland, or only one?

It happens in wayland only.

Thanks.

I'm seeing something very similar here. I just booted the neon-user-20240523-1335.iso ISO in QEMU (I'm running Ubuntu 22.04 as the host system).

Simply moving the mouse around gives me these messages in the system journal (journalctl | grep libinput):

May 23 18:55:55 neon kwin_wayland[1104]: kwin_libinput: Libinput: event2  - VirtualPS/2 VMware VMMouse: client bug: event processing lagging behind by 29ms, your system is too slow
May 23 18:55:56 neon kwin_wayland[1104]: kwin_libinput: Libinput: event2  - VirtualPS/2 VMware VMMouse: client bug: event processing lagging behind by 78ms, your system is too slow
May 23 18:56:01 neon kwin_wayland[1104]: kwin_libinput: Libinput: event2  - VirtualPS/2 VMware VMMouse: client bug: event processing lagging behind by 28ms, your system is too slow
May 23 18:56:05 neon kwin_wayland[1104]: kwin_libinput: Libinput: event2  - VirtualPS/2 VMware VMMouse: client bug: event processing lagging behind by 32ms, your system is too slow
May 23 18:56:38 neon kwin_wayland[1104]: kwin_libinput: Libinput: event2  - VirtualPS/2 VMware VMMouse: client bug: event processing lagging behind by 32ms, your system is too slow
May 23 18:56:38 neon kwin_wayland[1104]: kwin_libinput: Libinput: event2  - VirtualPS/2 VMware VMMouse: WARNING: log rate limit exceeded (5 msgs per 60min). Discarding future messages.

From what I undertand, kwin_libinput isn't able to keep up (dispatch) events fast enough and so libinput complains.

I also have this exact same behaviour on a custom image (yocto based) running plasma mobile.

Another thing to try is `sudo evtest`, select the first mouse (VirtualPS/2 VMware Mouse) and look at the events. The faster the mouse moves the 'jerkier' it gets. CPU usage for the kwin_wayland process also goes up substantially (~12%).

Note: doesn't happen when running on mutter, with the same QEMU setup.

kinfo:
Operating System: KDE neon 6.0
KDE Plasma Version: 6.0.4
KDE Frameworks Version: 6.2.0
Qt Version: 6.7.0
Kernel Version: 6.5.0-35-generic (64-bit)
Graphics Platform: Wayland
Processors: 2 × AMD Ryzen 9 7900 12-Core Processor
Memory: 7.7 GiB of RAM
Graphics Processor: virgl

Please attach the full output of
> journalctl --user-unit plasma-kwin_wayland --boot 0

Created attachment 170960 [details]
plasma-kwin_wayland service log

There you go.

Okay, KWin is using legacy modesetting, with XRGB8888 as the buffer format. I can't think of any reason this would be slow, without Xorg also being slow

(In reply to Zamundaaa from comment #8)
> Okay, KWin is using legacy modesetting, with XRGB8888 as the buffer format.
> I can't think of any reason this would be slow, without Xorg also being slow

Note that if my mouse cursor is _not_ on the QEMU window, the system doesn't experience slowdowns. It's only when I move the mouse that everything seems to slow down. For example, navigating the 'start' menu is very jerky in the VM but works fine on bare metal... very strange.

My QEMU configuration:

/usr/local/bin/qemu-system-x86_64 \
    -enable-kvm \
    -cpu host \
    -drive if=pflash,format=raw,unit=0,readonly=on,file=/usr/share/ovmf/OVMF.fd \
    -drive file=$image_file,if=virtio,format=raw \
    -device virtio-net-pci,netdev=net0 \
    -device virtio-rng-pci \
    -device virtio-vga-gl \
    -display gtk,gl=on \
    -m 8G,maxmem=16G \
    -machine q35,accel=kvm \
    -netdev user,id=net0,hostfwd=tcp::2222-:22,"${PORT_FWDS}" \
    -boot d \
    -drive file=/home/marc/Downloads/neon-user-20240523-1335.iso,media=cdrom,readonly=on \
    -smp 2

QEMU version: 9.0.0