9.3.3. Domain vCPU Threads

In addition to tuning domain processes, libvirt also permits the setting of the pinning policy for each vcpu thread in XML configuration. This is done inside the <cputune> tags:
	<vcpupin vcpu="0" cpuset="1-4,ˆ2"/>
	<vcpupin vcpu="1" cpuset="0,1"/>
	<vcpupin vcpu="2" cpuset="2,3"/>
	<vcpupin vcpu="3" cpuset="0,4"/>
In this tag, libvirt uses either cgroup or sched_setaffinity(2) to pin the vcpu thread to the specified cpuset.


For more details on cputune, refer to the following URL: http://libvirt.org/formatdomain.html#elementsCPUTuning
In addition, if you need to set up a virtual machines with more vCPU than a single NUMA node, configure the host so that the guest detects a NUMA topology on the host. This allows for 1:1 mapping of CPUs, memory, and NUMA nodes. For example, this can be applied with a guest with 4 vCPUs and 6 GB memory, and a host with the following NUMA settings:
4 available nodes (0-3)
Node 0:	CPUs 0 4, size 4000 MiB
Node 1: CPUs 1 5, size 3999 MiB
Node 2: CPUs 2 6, size 4001 MiB
Node 3: CPUs 0 4, size 4005 MiB
In this scenario, use the following Domain XML setting:
	<vcpupin vcpu="0" cpuset="1"/>
	<vcpupin vcpu="1" cpuset="5"/>
	<vcpupin vcpu="2" cpuset="2"/>
	<vcpupin vcpu="3" cpuset="6"/>
	<memory mode="strict" nodeset="1-2"/>
		<cell id="0" cpus="0-1" memory="3" unit="GiB"/>
		<cell id="1" cpus="2-3" memory="3" unit="GiB"/>