Only three qubes running(fedora-38-xfce):
With wi-fi connection on, but without any activity on my part, CPU usage of sys-net is ~2%, sys-firewall and dom0 – ~1%, sys-usb – 0%.
Without wi-fi connection CPU usage reduced to ~0% on all of qubes.
Is there any valid reason for this to be OK?
How can this be monitored/checked?
sys-net may be just seeing raw traffic on the network but the others would still be idle if there is nothing actually let in by sys-net to process. It seems legit to me.
Dom0> xl top
XL command above will show you the various runtime aspects of each vm, but since you already knew the cpu load I suspect you already knew that. Running top inside the individual idle vm’s will of course spike the cpu by virtue of running top just to see all the other individual processes that are currently idle. Anything you do inside the respective VM should of course show activity otherwise they should be idle.
I’m not sure what else you might be looking for in this response.