To make these settings persistent on 18.06.X and 19.07 it might make sense to add
echo 3 > /sys/class/net/eth0/queues/rx-0/rps_cpus
echo 3 > /sys/class/net/eth0/queues/tx-0/xps_cpus
to the end of /etc/hotplug.d/net/20-smp-tune as otherwise a hotplug event on eth0 will reset the values away from 3.