[libvirt] Question about save and restore OVS per-port data in live migration

[wangxin (U)]

Hi

When we try to migrate a guest with 12 NICs, we find libvirt will try
to get per-port data in finish phase, it makes the guest paused for
several hundred milliseconds.

  qemuMigrationCookieAddNetwork
    -> virNetDevOpenvswitchGetMigrateData for per-nic
      -> run 'ovs-vsctl --if-exists get Interface vnetx external_ids:Port'  (about 25ms)

In our case, there's no portData available and it seems there is no need to run the cmd.

Questions:
1. Is it necessary to get/set per-port data in migration finish phase? It will increase the downtime.
2. Is there any way (i.e. a switch) to not run the OVS cmd if there's no portData available?