Re: [Xen-devel] CAP and performance problem

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 06/06/13 14:55, Massimo Canonico wrote:
> On 06/06/2013 03:02 PM, Juergen Gross wrote:
> > 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? 
> Fedora, after few seconds, asks you which kernel do you want to use. 
> You can add some parameter in the command line who launches the 
> kernel. So, I add "cpufreq=none" in the command line.
> > And (please forgive
> > my paranoia) you rebooted the complete system after that?
> Your paranoia is also mine, I always reboot my machines. Thanks for 
> asking.
> > > 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?
> My virtual machines is called rubis-web and during "cap=50%" 
> experiment I can see this values in xentop for this specific domain.
> > Could you try:
> >
> > xl vcpu-list; sleep 10; xl vcpu-list
> >
> > when the test is running and post the output?
> >
> >
> > Juergen
> here we go:
>
> [root@csitest ~]# xl vcpu-list; sleep 10; xl vcpu-list
> Name                                ID  VCPU   CPU State   Time(s) CPU 
> Affinity
> Domain-0                             0     0    0   ---      23.0 0
> Domain-0                             0     1    0   ---      10.5 0
> Domain-0                             0     2    0   ---       8.5 0
> Domain-0                             0     3    0   r--       6.8 0
> rubis-web                            1     0    2   r--    2968.5 2
> Name                                ID  VCPU   CPU State   Time(s) CPU 
> Affinity
> Domain-0                             0     0    0   ---      23.0 0
> Domain-0                             0     1    0   r--      10.6 0
> Domain-0                             0     2    0   ---       8.5 0
> Domain-0                             0     3    0   ---       6.8 0
> rubis-web                            1     0    2   r--    2973.5 2
>
> Concerning the George's question:
> > Have you checked your BIOS for performance settings?
> I'm not sure what you mean for "BIOS perfomance settings". To my best 
> knowledge, in the BIOS I have to be sure that the "hw virtualization" 
> is enabled.
Some BIOSes have settings that will automatically mess around with the 
performance settings of the processor.  This could be automatically 
slowing the core down because it's only 50% busy. This would be 
different on each BIOS.  Just take a quick look for anything that seems 
to say something about performance, and set it to "max" or "performance" 
mode (as opposed to say, power-saving or balanced mode).
You might also try playing around with the "turbo" mode if it's 
available -- maybe the "turbo" mode takes a bit of time to get going, 
and running at 50% never kicks it in.  If you disable "turbo" mode, you 
may find that with no cap you get 450s instead of 300s.
 -George

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