Hi jiri, The actual utilization can never be greater than 400% i.e. 100% per vCPu. we are overcommitting by allocating 4 vCpus to both the VMs. if both the VMs are trying to use what is allocated then there will be contention for resources. During the contention the resource allocation is done differently in different hypervisors.
So in the scenario below both the apps cannot be happy if VM1 and VM2 want to use 350% and 360% at the same time. Overcommit is useful to increase the overall resource utilization. Overcommit is useful if the scenario was say VM1 uses 300% and VM2 uses 100% during 10-11 am and form 11-12am VM2 uses 300% where as VM1 uses 100%. we have overcommitted the resource by allocation more than what we have, this will keep the cpu utilization of the host near 100% most of the time and we will be able to launch more VMs as not all the VMs try to use the resource allocated to them at the same time. Regards, Bharat. On Aug 16, 2013, at 9:28 AM, Jerry Jiang <[email protected]> wrote: > HI all, > > > > I have question not figured out very well. (may not for CS, but I noticed CS > supports CPU over-commitment) > > > > Imaging the following case, > > > > A host owns 4 physical CPUs > > Because apps on VM1 consume 350% CPU during 10am-11am, so I gave VM1 4 vCPUs > to ensure performance > > Because apps on VM2 consume 360% CPU during 10am-11am, so I gave VM2 4 vCPUs > to ensure performance > > > > So I would ask if Apps are both happy with vm1 and vm2 during 10am-11am > > > > If not, Is CPU over-commitment meaningful? How is your guys consider the > over-commitment > > > > Thanks > > Jerry > > >
