actually I have no problems with usage of my cpu during this tests.
Not on the kvm-host and not inside the guest:
KVM-Guest
top - 08:50:55 up 11:25, 1 user, load average: 0.43, 0.14, 0.05
Tasks: 81 total, 1 running, 80 sleeping, 0 stopped, 0 zombie
Cpu0 : 0.1%us, 0.4%sy, 0.0%ni...