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Re: [Xen-devel] CAP and performance problem

  • To: Massimo Canonico <mex@xxxxxxxxxxxx>
  • From: Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>
  • Date: Thu, 06 Jun 2013 15:02:59 +0200
  • Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>, Dario Faggioli <dario.faggioli@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxx
  • Delivery-date: Thu, 06 Jun 2013 13:06:46 +0000
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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


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

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 Gross                 Principal Developer Operating Systems
PBG PDG ES&S SWE OS6                   Telephone: +49 (0) 89 3222 2967
Fujitsu Technology Solutions              e-mail: juergen.gross@xxxxxxxxxxxxxx
Domagkstr. 28                           Internet: ts.fujitsu.com
D-80807 Muenchen                 Company details: ts.fujitsu.com/imprint.html

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