Re: [Xen-users] Does Xen's Dom0 hypervisor based cpufreq support 'schedutil' governor?

[lists@xxxxxxxxxxxx]

On Tue, Aug 23, 2016, at 11:55 AM, Austin S. Hemmelgarn wrote:
> As far as I understand it, they are independent of the Domain-0 cpufreq 
> governors (or if they aren't, then Linux and NetBSD have identical 
> behavior in their CPU frequency governors, which would not surprise me 
> all that much).
>
> Assuming that's the case, 'ondemand' is the closest to 'schedutil', as 
> schedutil in Linux is just a smarter version of the ondemand governor. 
> Ondemand takes only the processor utilization and the current frequency 
> into account, while schedutil also factors in a bunch of other things.
> 
> I'm not a Xen developer myself, but based on my very limited knowledge 
> of the internals of Xen and my marginally greater knowledge of the 
> internals of Linux, I'd say it's not likely that a governor equivalent 
> to schedutil is even possible on Xen without all the domains 
> co-operating (a lot of the stats that schedutil looks at are derived 
> from parts of the process state which would translate to guest kernel 
> internal state in the context of Xen).

In Dom0, with cpufreq=xen set (i.e. hypervisor based cpufreq in use) it looks 
like 'ondemand' is the default

        xenpm  get-cpufreq-para all | egrep "scaling_driver|current"
                scaling_driver       : acpi-cpufreq
                current_governor     : ondemand
                scaling_driver       : acpi-cpufreq
                current_governor     : ondemand
                scaling_driver       : acpi-cpufreq
                current_governor     : ondemand
                scaling_driver       : acpi-cpufreq
                current_governor     : ondemand

Notice that the scaling driver is apci-cpufreq -- which is the same as what the 
kernel would use in a non-Xen env.

It'd be nice to find an up to date, authoritative doc on this.  It's pretty 
confusing .





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