Now that we have set up the guest virtual machine instances so that they will only be allowed to run on cores 2, 3, 6, and, 7 we must also set up the host processes so that they will not run on these cores – restricting themselves instead to cores 0, 1, 4, and 5. To do this we must set the isolcpus kernel argument – adding this requires editing the system’s boot configuration.

Source: Driving in the Fast Lane – CPU Pinning and NUMA Topology Awareness in OpenStack Compute