Re: [Xen-devel] CAP and performance problem

[Massimo Canonico <mex@xxxxxxxxxxxx>]

I have run other tests, changing the run duration but
it seems that CAP mechanism has some problem.

I always get response time too much longer (3 times instead of 2).

Any idea about how to fix the problem?

Did someone try to make a similar experiment?

Thanks,
 M


On 05/21/2013 04:47 PM, Dario Faggioli wrote:
> 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

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