Re: CAP and performance problem

[Juergen Gross <juergen.gross@ts.fujitsu.com>]

On 06.06.2013 14:52, 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

You added the boot parameter for the hypervisor, not dom0? And (please forgive
my paranoia) you rebooted the complete system after that?

> 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)

What was the load reported by xentop for your domu?

Could you try:

xl vcpu-list; sleep 10; xl vcpu-list

when the test is running and post the output?


Juergen

-- 
Juergen Gross                 Principal Developer Operating Systems
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