Queens steal time [nova]

Budai Laszlo laszlo.budai at gmail.com
Thu Nov 12 17:35:56 UTC 2020

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,

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 <mailto: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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