Question regaring correct usage of CPU shares

Hi there, I have a question regarding the shares option of the cputune section. I want to illustrate my question with the following example. Let's assume I have two virtual machines like the following on four dedicated core with two threads each: VM1: <cputune> <shares>512</shares> <vcpupin vcpu="0" cpuset="0"/> <vcpupin vcpu="1" cpuset="4"/> </cputune> VM2: cputune> <shares>512</shares> <vcpupin vcpu="0" cpuset="1"/> <vcpupin vcpu="1" cpuset="5"/> <vcpupin vcpu="2" cpuset="2"/> <vcpupin vcpu="3" cpuset="6"/> <vcpupin vcpu="4" cpuset="3"/> <vcpupin vcpu="5" cpuset="7"/> </cputune> Those two virtual machines I just mentioned won't interfere with one another since they are pinned to different cores. However I introduce another, third virtual machine, like this: VM3: <cputune> <shares>512</shares> <vcpupin vcpu="0" cpuset="0"/> <vcpupin vcpu="1" cpuset="4"/> <vcpupin vcpu="2" cpuset="1"/> <vcpupin vcpu="3" cpuset="5"/> <vcpupin vcpu="4" cpuset="2"/> <vcpupin vcpu="5" cpuset="6"/> <vcpupin vcpu="6" cpuset="3"/> <vcpupin vcpu="7" cpuset="7"/> </cputune> What I want is that VM1, VM2 and VM3 all receive half of the cores CPU time if congestion appears. My question is how the shares are calculated. Are they calculated on a per core basis? Meaning VM1 and VM3 use the first core so each will get half of the cores capacity when congestion appears, or are the shares calculated over all cores a virtual machine uses and I need to scale the amount of shares with increasing number of cores. What is the correct setting here so that all virtual machines in this example are guaranteed half of the capacity of each of their respective cores if congestion appears? Thank you.