Performance statistics directly from hypervisor

I am starting a new project based on performance analysis using kvm where the goal is basically to gather the more information as possible about a given VM by neither installing any tool on it nor accessing it directly. In other words, I hope to collect metrics like CPU usage, I/O rates, etc. only through hypervisor analysis. I have found out that I can do something by using libvirt API but in this first step of the project, instead of start programming new tools I would like to just know which statistics/metrics I could acquire with this approach. The closer I got was a tool called host-sflow and another one called collectd, which are supposed to collect statistics from hypervisor. The problem is that they don’t tell a priori which metrics they provide…
Unfortunately I haven’t found much useful information on official documentation as well. So, I would highly appreciate any help coming from you guys. If any point is unclear, please let me know.

Best Regards,