[ovs-dev] What's the difference between system datapath and netdev datapath?

[ry0117]

Hi ,all:
    Is there anyone know the difference between system datapath and netdev datapath?
I created a bridge in system datapath with a phyical port, and add flow to it, it worked fine.
Then I created a bridge in netdev datapath and add a dpdk port to it, then add the  same flow to it,
But the netdev datapath bridge doesn't work--I don't get any connectivity when I do this. Why?
What should I do to make the bridge work fine in netdev datapth?