Created attachment 164429 [details] screenshot of the issue SUMMARY The system monitor uses ~70% of the cpu. STEPS TO REPRODUCE 1. Download KDE Neon unstable 2023-12-24 (neon-unstable-20231224-1120.iso) 2. Run in a qemu vm with 4 cores and 4GB of memory and virtio-gpu graphics and KVM vm hardware acceleration: `qemu-system-x86_64 -cpu max -machine q35,accel=kvm -m 4096 -smp 4 -device virtio-net,netdev=net0 -netdev user,id=net0 "$@" -cdrom ~/Downloads/neon-unstable-20231224-1120.iso -chardev stdio,mux=on,id=char0 -mon chardev=char0,mode=readline -vga virtio` 3. Run the system monitor inside the vm. OBSERVED RESULT The system monitor uses ~70% of the cpu. EXPECTED RESULT The system monitor uses at most 1-2% of the cpu. SOFTWARE/OS VERSIONS Linux/KDE Plasma: (available in About System) KDE Plasma Version: 5.91.90 KDE Frameworks Version: 5.248.0 Qt Version: 6.6.1 ADDITIONAL INFORMATION https://bugs.kde.org/show_bug.cgi?id=475951 seems related, but that talks about cpu usage spikes, while for me it is consistently high cpu usage.
This happens when the llvmpipe graphics driver is used
Created attachment 164476 [details] Hotspot analysis
The charts used by System Monitor use GPU based rendering, which means that LLVMpipe needs to emulate all the shader logic normally done by a GPU. This is pretty heavy for most CPUs, so you end up with a lot of CPU usage. There is not a whole lot we can do about that, as can be seen in the hotspot screenshot most of the time is taken by the LLVMpipe rasterizer.