Re: [Xen-devel] CAP and performance problem

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 06/06/13 13:52, Massimo Canonico wrote:
> On 06/06/2013 12:44 PM, George Dunlap wrote:
> > 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
> Unfortunately, this did not change much. I set "cpufreq=none" in the 
> boot line and restart my experiment.
> With no cap I got 298.029
> with cap=50% I got 910.272
> (average values of 3 experiments for each cap setting)
>
> dom0 load during the experiment is less than 1% (that says xentop)
Have you checked your BIOS for performance settings?

 -George

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