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Re: [Xen-devel] CAP and performance problem

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

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?


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...


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