Re: [Xen-devel] CAP and performance problem

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 06/06/13 11:39, Juergen Gross wrote:
> On 06.06.2013 10:57, Massimo Canonico wrote:
> > On 06/06/2013 10:37 AM, Dario Faggioli wrote:
> > > On mer, 2013-06-05 at 19:05 +0200, Massimo Canonico wrote:
> > > > Hi Dario,
> > > > and thanks for these test.
> > > >
> > > > I forgot to ask you which xen version has beed used for your 
> > > > experiments.
> > > Yeah, me too! :-)
> > >
> > > I'm using xen-unstable, pulled yesterday (commit id
> > > e430510e5cbbfcdc1077739292def633e70fedea), compiled and installed on a
> > > Debian unstable system. Dom0 kernel is a bit old, as it's a 3.6.
> > >
> > > What about you?
> > xen 4.2.2
> > kernel dom0: 3.8.11-200.fc18.x86_64
> Just had an idea: is there any other load on the system during your 
> test (other
> domains, dom0 load)? If not, it could be that the power management is 
> reducing
> the cpu speed during idle (when the cap applies). This could lead to 
> reduced
> performance overall.
>
> You can test this by setting the xen hypervisor boot option
>
> cpufreq=none
>
> and run your test again (with and without cap).
Ah, genius Juergen!  That would make total sense.

 -George


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