[ovirt-users] Ovirt VM Performance abd CPU times

[Daniel Helgenberger]

On 29.10.2014 15:57, Xavier Naveira wrote:
> On 10/29/2014 03:07 PM, Xavier Naveira wrote:
>> On 10/29/2014 01:26 PM, Daniel Helgenberger wrote:
>>> On 29.10.2014 11:48, Xavier Naveira wrote:
>>>> On 10/29/2014 11:47 AM, Xavier Naveira wrote:
>>>>> On 10/29/2014 11:40 AM, Daniel Helgenberger wrote:
>>>>>>
>>>>>>
>>>>>> On 29.10.2014 10:21, Xavier Naveira wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> We are migrating our ifrastructure from kvm+libvirt hypervisors to
>>>>>>> ovirt.
>>>>>>>
>>>>>>> Everything is working fine but we're noticing that all the qemu-kvm
>>>>>>> processes in the hypervisors take a lot of CPU.
>>>>>> Without further details of the workload this is hard tell. One
>>>>>> Reason I
>>>>>> can think of might be KSM [1]. Is it enabled on your cluster(s)?
>>>>>> What is
>>>>>> your mem over-commitment setting?
>>>>>>
>>>>>> Note, IIRC the KSM policy is currently hard coded; it will start at
>>>>>> 80%
>>>>>> host mem usage.
>>>>>>
>>>>>> [1] http://www.ovirt.org/Sla/host-mom-policy
>>>>>>>
>>>>>>> The typical example is an idle machine, running top from the machine
>>>>>>> itself it reports cpu use percentages below 10% and loads (with 2
>>>>>>> processors) of 0.0x. The process running that machine in the
>>>>>>> hypervisor
>>>>>>> rports cpu uses in the order of the 80-100%.
>>>>>>>
>>>>>>> Should the values look like this? Why are the idle machines eating
>>>>>>> up so
>>>>>>> much CPU time?
>>>>>>>
>>>>>>> Thank you.
>>>>>>> Xavier
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> Users mailing list
>>>>>>> Users at ovirt.org
>>>>>>> http://lists.ovirt.org/mailman/listinfo/users
>>>>>>>
>>>>>>
>>>>>
>>>> Hi, thank you for the answer.
>>>>
>>>> I've been trying to work out some pattern and realized that the VMs
>>>> using that much cpu all are Redhat 5.x, the Readhat 6.x doesn't exhibit
>>>> this kind of high cpu use. (we run only redhat/centos 5.x/6.x on the
>>>> cluster)
>>> What OS are the hosts running? In case of EL6, make sure you have
>>> tuned-0.2.19-13.el6.noarch installed [1].
>>
>> That's exactly the version we've in the hypervisors.
>>
>>>
>>> To further investigate please post Engine, VDSM, libvirt and kernel
>>> versions from the hosts.
>>
>> vdsm-xmlrpc-4.14.11.2-0.el6.noarch
>> vdsm-cli-4.14.11.2-0.el6.noarch
>> vdsm-python-4.14.11.2-0.el6.x86_64
>> vdsm-4.14.11.2-0.el6.x86_64
>> vdsm-python-zombiereaper-4.14.11.2-0.el6.noarch
>>
>> libvirt-client-0.10.2-29.el6_5.12.x86_64
>> libvirt-0.10.2-29.el6_5.12.x86_64
>> libvirt-lock-sanlock-0.10.2-29.el6_5.12.x86_64
>> libvirt-python-0.10.2-29.el6_5.12.x86_64
>>
>> 2.6.32-431.23.3.el6.x86_64 #1 SMP Wed Jul 16 06:12:23 EDT 2014 x86_64
>> x86_64 x86_64 GNU/Linux
>>
>>
>>>
>>> [1] https://access.redhat.com/solutions/358033
>>>>
>>>> I'll take a look to the KSM config.
>>>>
>>>> Cheers,
>>>>
>>>> Xavier
>>>>
>>>
>>
>
> Actually, this seems to be it. But I'm already at a newer kernel:
> https://bugzilla.redhat.com/show_bug.cgi?id=705082
Well, I do not have such hardware so I never run into the issue. You 
could disable HT as I suspect your physical cores are less then 64?

Your workload might differ but my VMs usually do not benefit from 
'threaded' cores and I want HT disabled anyway. Also, you can check 
cluster settings and disable 'count threads as cores' if enabled. But I 
think this might not make any difference.
>

-- 
Daniel Helgenberger
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