Test with OVS example failed when exec ovs-vsctl add-port

I'm trying to do the test acording to the dev-quickstart.rst
when exec bash ~/networking-generic-switch/devstack/exercise.sh
the following error happened:
ovs-vsctl: Error detected while setting up 'p_01'. See ovs-vswitchd log for details.
here is the command:
sudo ovs-vsctl add-port genericswitch p_01

the root cause is that the port's name should be a exist interface use ifconfig to see, such as eth0. If you just want to use a virtual port name to make a test you should specify the port's type like ovs-vsctl add-port genericswitch p_01– set Interface port0 type=internal

so I changed the command as following
sudo ovs-vsctl add-port genericswitch p_01 – set Interface p_01 type=internal

this time it worked for me.