Re: [Xen-devel] RFC: cpu frequency scaling

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 25/10/06 7:04 pm, "Rik van Riel" <riel@xxxxxxxxxx> wrote:

> These approaches both have their drawbacks.  One requires porting over
> a series of drivers from Linux to the hypervisor, maintaining two sets
> into the future.  The second could mess up some of the credit
> scheduler's balancing, and requires Linux modifications to poll the
> hypervisor for the CPU load...
> 
> Also, it would mean the end of running a 1 vcpu small dom0, which some
> people seem to like.
> 
> Which of these approaches would you prefer?

Frequency changes in dom0, please. The 'small dom0' issue is easily handled
-- create a driver domain to handle the frequency management. Or move the
potentially resource-intensive processes in dom0 out to a domU (amounts to
the same thing, really). It ought to take little enough resource that having
a VCPU per PCPU should not affect scheduling of more user-visible VMs.

We want to have the flexibility to implement cpufreq policy in a user-space
process anyway, so the feedback loop requires an interface to be punched
through between Xen and a cpufreq-managing guest.

 -- Keir



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