Everything Is Your Own Fault - Downside of virt-manager
Using libvirt and virt-manager does reduce the number of known features that need attention, but it also doesn't offer you any help by providing useful features.
After setting up libvirt with virt-manager I followed some guides on performance optimisation -
Reading these guides made it clear that real performance optimisation can quickly get complex and requires deep knowledge of kernel features.
Turns out that management tools like oVirt provide a one-click solution to apply many optimization settings at once: oVirt 4.2 introducing High Performance VM profile 😒
It's nice to learn about all these features by reading documentation and guides - but sometimes a little bit more convenience is just nice to have.