Re: Performance difference between Xen versions

["Jan Beulich" <JBeulich@novell.com>]

>>> On 06.05.11 at 15:49, Juergen Gross <juergen.gross@ts.fujitsu.com> wrote:
> Okay, I think I understand the basic mechanisms of cpufreq stuff now :-)
> I propose the following changes:
> 
> - Cpupools get a new parameter "cpufreq" which is similar to the hypervisor
>    boot parameter. It is valid if the hypervisor is responsible for cpufreq
>    handling (this excludes cases cpufreq=none and cpufreq=dom0-kernel)
> - Cpupool0 is initialized with the boot parameter settings, new cpupools are
>    created with the cpupool0 settings, they get their new cpufreq parameters
>    via libxl later (this avoids changing the interface for cpupool creation, 
> I 
> only
>    need a new interface to set the cpufreq parameters for a cpupool, which
>    can be used for changing the settings, too. This interface could take the
>    cpufreq parameters as text string resulting in support of exactly the 
> same
>    parameters as the hypervisor).
> - cpufreq_policy is only spanning multiple cpus of one cpupool (if at all). 
> This
>    requires a check for the max frequency to be set in a frequency domain
>    if the frequency of a processor is changing. This is similar to the 
> ondemand
>    governor, but might cross cpufreq_policy boundaries.
> 
> Did I miss anything? Any other suggestions?

There are cases (hyperthreads, and iirc also some AMD CPUs) where
altering the frequency of one CPU at once alters that of others, and
if those live in distinct pools things are going to become "interesting".

Jan

> 
> 
> Juergen