Re: CAP and performance problem

[Massimo Canonico <mex@di.unipmn.it>]

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)

Thanks,
  M