Comment 0 for bug 1836713

Upgrading and existing openvswitch installation which has been manually configured to use the DPDK alternative binary using:

  sudo update-alternatives --set ovs-vswitchd /usr/lib/openvswitch-switch-dpdk/ovs-vswitchd-dpdk

results in the ovs-vswitchd being reset back to 'auto':

Setting up openvswitch-switch (2.11.0-0ubuntu2~cloud0) ...
update-alternatives: using /usr/lib/openvswitch-switch/ovs-vswitchd to provide /usr/sbin/ovs-vswitchd (ovs-vswitchd) in auto mode

The prerm maintainer scripts always remove the alternatives, which purges any manual setting done of the binaries.