Eric Blake

In the case of the memory balloon device, libvirt CAN provide stats from
the guest, because of the way the balloon device works. But if you
aren't using a balloon, or if the guest is not cooperative, this won't
work. Better would be a guest-agent command for getting at this
information (but again, you are relying on guest cooperation). In
short, libvirt is great at stats from the HOST point of view, but for
stats from the GUEST point of view, you are often better off using the
same mechanisms that you would for getting stats from a remote bare
metal machine, without needing libvirt in the mix.