On Thu, Mar 16, 2017 at 12:14:31AM +0300, Vasiliy Tolstov wrote:

> 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)

There's no way to do this at a KVM or libvirt level. The host kernel will
always auto-scale CPU frequency according to the load placed on them by
the guest OS (and other processes).

To get a fixed frequency,and predictable benchmark results you would
have to first use CPUAffinity in systemd.conf (or equiv) to ensure
no other OS processes run on a particular chosen CPU. Then strictly
bind the guest vCPU to that host CPU. Finally you would have to
use sysfs to set the scaling_max_freq/min_freq to contrl what speed
your host CPUs ran at.




Regards,
Daniel
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