----- Original Message ----- > From: "Abhishek Talwar/HYD/TCS" <abhishek.talwar at tcs.com> > To: openstack-dev at lists.openstack.org > > Hi Folks, > > When we boot an instance and assign a flavor to it, how are the vcpu's, ram > given to the instance. Actually the question is this while creating an > instance we must be assigning it some Vcpu's according to the flavor we gave > to the instance. So where are these Vcpu's placed and how are they mapped > with an instance. By default we do not assign the instances vCPUs to specific pCPU cores - instead just passing a number of vCPUs to give to the instance to qemu. As of Kilo CPU pinning functionality is available but it is somewhat indirect (see http://specs.openstack.org/openstack/nova-specs/specs/kilo/implemented/virt-driver-cpu-pinning.html ). > Suppose I want to add some more Vcpu's to my VM at runtime without changing > my flavor to a bigger one, can I do it ? What you are effectively asking for here is hot resize. Most modern hypervisors including KVM have some concept of being able to do this but it's not currently exposed through Nova, though it has been proposed in the past. This appears to be the most recent proposal of this ilk: https://blueprints.launchpad.net/nova/+spec/instance-live-resize I would recommend reviewing and commenting on the latest specification if this is of interest to you: https://review.openstack.org/#/c/141219/ Thanks, Steve