Queens steal time [nova]

Laurent Dumont laurentfdumont at gmail.com
Thu Nov 12 19:10:30 UTC 2020

Is the vCPU placement the same between the two? (if you do a virsh dumpxml
of all the VMs on the compute, you should be able to see the which vCPU
we're mapped to which VM CPU). The same VMs under a Kilo compute are seeing
different Steal % when the compute is upgraded to Queens? I guess that
overall % Steal will also be impacted by how busy and noisy the VMs are.

My knowledge is far from exhaustive but I would be surprised at a loss of
CPU performance between Kilo and Queens.

On Thu, Nov 12, 2020 at 12:35 PM Budai Laszlo <laszlo.budai at gmail.com>

> Hi Laurent,
> Thank you for your answer.
> I agree with you that without the pinning the steal time can appear
> anytime. What is strange to me that in openstack Kilo the steal is
> significantly smaller even when there is some overcommit. So I am wondering
> where to look for the difference?
> Kind regards,
> Laszlo
> On 11/12/20 5:01 PM, Laurent Dumont wrote:
> Hi,
> Technically, I think that you always run the chance of "steal" time if you
> don't pin CPUs. I'm not sure if Openstack is "smart" enough to allocate
> CPUs that are not mapped to anyone in sequence (and start to overcommit
> once it's necessary. You might have 42 out of 48 free CPUs but I don't
> think that means that Openstack will prevent two VM from getting the same
> CPU scheduled (without CPU pinning).
> On Thu, Nov 12, 2020 at 9:09 AM Budai Laszlo <laszlo.budai at gmail.com>
> wrote:
>> Hello all,
>> we are comparing the behavior of our queens  openstack with kilo. In
>> queens we are observing an increase in the steal time reported in the guest
>> along with the increase of the load averages. All this is happening while
>> the host is not overloaded, and reports 80+ idle time
>> Initially we have suspected that the overcommit might be the reason of
>> the steal, so we have migrated vms, and now there are 42 vCPUs used out of
>> the 48 pCPUs, but in the guest we still observe the steal time.
>> with similar configuration in openstack kilo we see smaller load, and
>> almost no steal time at all.
>> what could be the reason of this steal time when there is no CPU
>> overcommit?
>> Thank you for any ideas.
>> Kind regards,
>> Laszlo
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