[libvirt] limit cpu speed in domain xml

Hi. Does it possible to limit vm cpu speed for example to 1Ghz or 500Mhz ? I need to simulate some hardware with specific cpu speed and test my application inside this vm , i want to measure results from each test and need constant cpu speed for testing (i need to run test not only my notebook but on server too and want identical cpu speed inside vm) -- Vasiliy Tolstov, e-mail: v.tolstov(a)selfip.ru