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:
<cputune>
<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"/>
</cputune>
<cputune>
<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"/>
</cputune>
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In this tag, libvirt uses either cgroup or sched_setaffinity(2)
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
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
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In this scenario, use the following Domain XML setting:
<cputune>
<vcpupin vcpu="0" cpuset="1"/>
<vcpupin vcpu="1" cpuset="5"/>
<vcpupin vcpu="2" cpuset="2"/>
<vcpupin vcpu="3" cpuset="6"/>
</cputune>
<numatune>
<memory mode="strict" nodeset="1-2"/>
</numatune>
<cpu>
<numa>
<cell id="0" cpus="0-1" memory="3" unit="GiB"/>
<cell id="1" cpus="2-3" memory="3" unit="GiB"/>
</numa>
</cpu>
<cputune>
<vcpupin vcpu="0" cpuset="1"/>
<vcpupin vcpu="1" cpuset="5"/>
<vcpupin vcpu="2" cpuset="2"/>
<vcpupin vcpu="3" cpuset="6"/>
</cputune>
<numatune>
<memory mode="strict" nodeset="1-2"/>
</numatune>
<cpu>
<numa>
<cell id="0" cpus="0-1" memory="3" unit="GiB"/>
<cell id="1" cpus="2-3" memory="3" unit="GiB"/>
</numa>
</cpu>
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Red Hat Summit
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