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Re: [Xen-devel] CAP and performance problem

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


and run your test again (with and without cap).

Ah, genius Juergen!  That would make total sense.


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?


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