[libvirt] limit cpu speed in domain xml

[Vasiliy Tolstov]

16 Мар 2017 г. 13:18 пользователь "Daniel P. Berrange" <berrange at redhat.com>
написал:

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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Thanks! Next question, does it possible to provide constant speed for vps
in case of cloud service? For example user buy vps with 500mhz or 1ghz and
pay for guaranteed resource?
Weights not very useful because I can't guarantee that each vps have needed
processor time...
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