Xen can allocate virtual CPUs to associate with one or more host CPUs. This allocates real processing resources to guests. This approach allows Red Hat Enterprise Linux optimize processor resources when employing dual-core, hyper-threading, or other CPU concurrency technologies. The Xen credit scheduler automatically balances virtual CPUs between physical ones, to maximize system use. Red Hat Enterprise Linux allows the credit scheduler to move CPUs around as necessary, as long as the virtual CPU is pinned to a physical CPU.
If you are running I/O intensive tasks, it is recommended to dedicate either a hyperthread or an entire processor core to run domain0.
Note that this is unnecessary for KVM as KVM uses the default Linux kernel scheduler.
CPU affinities can be set with