Re: [Qemu-devel] Qemu-KVM: Virtual Machine Power Managment

[Eduardo Habkost]

On Thu, Nov 06, 2014 at 02:52:02PM +0000, Carew, Alan wrote:
> Hi folks,
> 
> I am looking for feedback regarding work-in-progress or planned CPU power
> management features for Qemu-KVM based Virtual Machines.
> 
> Looking back through the mailing list archives I did not find any discussion
> or patches relating to the general problem of virtual machine power
> management.
> 
> Currently the MSRs for power management are not exposed to a guest OS and as
> far as I am aware no abstraction driver exists to facilitate acpi_cpufreq like
> features on a guest.
> 
> The context for my query relates to deterministic power management at the
> application level(non-VM), where in certain domains the workload is 
> partitioned
> on a per core basis(1:1 thread-core exclusive pinning) and based on current
> workload an application thread can request a transition to a different 
> P-State,
> for example using the apci_cpufreq userspace power governor.
> 
> Are there any plans or previous discussion that I missed for exposing such an
> ability or similar for Qemu-KVM based virtual machines.

I am not aware of any previous discussion, either. One problem I see is
that you probably don't just need the VCPUs (or other VM-related tasks)
to be pinned to specific host CPUs, but you also want to make sure that
no other task in the system will unexpectedly run on that host CPU.

How is that normally achieved when no VMs are involved? Does the system
administrator have to ensure that no other processes are running at all,
or is there some software component that implements this and makes it
easier to set up?

-- 
Eduardo