Editing /etc/libvirt/qemu/$VM.xml
under libvirt's hands is not what you should do, neither is setting the affinity without libvirt. In that case libvirt doesn't know about the settings.
The right thing to do is use 'virsh edit $VM', set what you want and stop and start the domain. You can also use virsh
to pin each vCPU to particular host CPU(s):
for i in {1..X}; do # X is the number of VCPUs
virsh vcpupin $VM 0 1,3
done
virsh emulatorpin $VM 1,3
or
virsh numatune $VM --nodeset 1,3 # To pin to particular
You can use '--config' and '--live' to set it in config or for live domain respectively. For further options see the manual for comman virsh
(man virsh
).