Re: [Xen-devel] CAP and performance problem

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On mar, 2013-05-21 at 15:28 +0100, Massimo Canonico wrote:
> On 05/21/2013 03:06 PM, Dario Faggioli wrote:
> > 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.
>
Ok.

> > 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?
> 
Sort of. However, since (you said) you have 4 cores, what I was thinking
was more a situation where you have the 4 Dom0 vCPUs pinned to cores
0-2, and the VM vCPU pinned to core 3.

You should be able to achieve that by doing right this:

# xl vcpu-pin 0 all 0-2
# xl vcpu-pin rubis-web all 3

Does it make sense? Oh, and also, you have 4 _actual_cores_, right? Or
is there any hyperthreading involved?

Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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