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Re: [Xen-devel] CAP and performance problem

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?


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


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
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?


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