Red Hat Training

A Red Hat training course is available for Red Hat Enterprise Linux

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:
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"/>