Re: [Xen-devel] cpufreq implementation for OMAP under xen hypervisor.

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 22 Aug 2014, Vitaly Chernooky wrote:
> On Fri, Aug 22, 2014 at 2:05 AM, Stefano Stabellini 
> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
>       It is not stupid, it is actually possible to do it that way.
> 
>       It would be similar to do cpufreq in dom0: anything you can run in Dom0,
>       you can also run separately in a little stubdom.
> 
>       However I think that it would be best to do it in Xen.
> 
> 
> Ok, what the reason is to prefer to do cpufreq in Xen?
> 
> With driver domain we can once provide stable binary ABI for cpufreq and do 
> not have any confusion with sources,
> patches and branches. If we will do cpufreq in Xen I expect in the nearest 
> future large amount of patches for cpufreq
> for wide variety of ARM platforms.
 
The reason is that cpu virtualization is done by Xen. The guest
operating system doesn't actually know anything about physical cpus,
because it is running on virtual cpus.

So it is OK to let a guest operating system manage one or more physical
devices. On the other hand letting it manage one ore more physical cpus
is more of a layering violation.

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