Openstack-Train VCPU issue in Hyper-V

Sean Mooney smooney at
Fri Aug 14 12:46:39 UTC 2020

On Fri, 2020-08-14 at 17:12 +0530, its-openstack at wrote:
> Dear Team,
>    We are using Openstack-Train in our organization.We have created windows server 2016 Std R2 instances with this
> flavor m5.xlarge ( RAM - 65536 , Disk - 500 , VCPUs - 16 ).Once Hyper-V future enabled in this instances VCPU count is
> automatically reduced to 1 core after restart.Even we have enabled nested virtualisation in openstack compute server.
just to confirm you are using the hyperv driver? if so then this sound like a hyperv bug not an openstack bug.
have you reached out to microsfot for support with this issue.

openstack itself does not garentee neted virt will be avaiable or work and doe not guarentee that
it will work across operationg systems.
> Please help us to short out this issue.
im off today so i wont be monitoring this i just saw your email while i was doing something else but without more info
of what your configurtion is and how this is failing i dont think people will be able to help you root cause your issue.
the other thing to be aware is that this is not a support list, peopel might have time to help and often do try to help
but outside of there good nature if you have an issue you can resolve your self withpointer form the comunity you might
need to reach out to your openstack vendor for support or if you dont have one engage one of your engeiner to work
with the upstream comunity to rootcause and fix the issue. there is not vendor customer support relationship betten
upstream and those that install it. the list acks as a way for people that develop and use openstack to help each other
> #cat /sys/module/kvm_intel/parameters/nested
> Y
are you setting this on the host if so that implies you are using the libvirt driver and instead rung windows server
as a guest and trying to enable hyperv on a windwos guest.  that is not whoe your email initally reads and is a differnt
part of teh code base.  when you say you enable the Hyper-V future is that in the windows os on the host or in a windows
os on a vm hosted on a linux host.

i dont know of any way that that could alter the vcpu allocated to the vm.

if you are using the libvirt dirver can you provide the xml before and after you enable the hyperv feature and reboot
if they are still the same then this is a windows kernel bug.  if you are not enabling the hyperv featre in the windows
os and are instead refering to modifying the libvirt xml to add hyperv feature flags to the gust  that is not supported.
you are not allowed to ever modify a nova crated guest xml. the wya to enable the hyperv enlightlment is to set
metadata on the glance image to delcare the image as a windows image and then nova will enabel the hyperv enlightement
feature flags in the xml.

> Regards,
> Sysadmin.

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