Re: [Xen-devel] CAP and performance problem

[Massimo Canonico <mex@xxxxxxxxxxxx>]

Hi Dario,
inline my answers
On 05/21/2013 03:06 PM, Dario Faggioli wrote:
> On mar, 2013-05-21 at 13:54 +0200, Massimo Canonico wrote:
> > Hi George,
> > thanks for your answer.
> >
> > Our physical machine has two processors and two cores for each processors.
> >
> > The virtual machine where our application run has just one VCPU that is
> > pinned to a single core.
> > Instead, dom0 was not pinned to any particular core.
> Ok, and what are you doing in Dom0? I guess almost nothing, is that the
> case?
yes
> Also, when inspecting the vCPU utilization, do you see the VM vCPU busy
> up to 100% without cap (or with cap set to 100) and, OTOH, up to 50%
> with cap set to 50?
I have monitored the CPU usage with xentop during the experiment and
I got what you said: my application always use the total amonut of CPU 
available.
> Well, looks like a scheduling issue, or, in any case, one where
> something is interacting with the scheduling. Can you perhaps boot Dom0
> so that it uses only 2 or 3 cores (or arrange for that later, e.g., with
> cpupools) and pin the vCPU of the VM on the 4th one?
In my experiments, I pin the vCPU of the VM on one core and other cores 
are pinned to Dom0.
[root@csitest ~]# xl vcpu-list
Name                                ID  VCPU   CPU State   Time(s) CPU 
Affinity
Domain-0                             0     0    0   ---     383.3  0
Domain-0                             0     1    0   -b-     358.1  0
Domain-0                             0     2    0   -b-     224.3  0
Domain-0                             0     3    0   r--     256.8  0
rubis-web                            1     0    2   -b-    9250.9  2

(rubis-web is, of course, the VM where my application run)

Is this configuration what you meant?

Thanks,
 Massimo



> I'm not sure what could be going on, but that sounds a reasonable way to
> rule out as much room for interference as possible...
>
> Dario

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