OFP-Li: add-flow RPC is slow; 2 flow entries per sec.

What I used
-----------

OpenFlow version: OF13
Target OFP: OpenFlow plugin Lithium version
Application: VTN Manager ("odl-vtn-manager-rest" feature)
Problem RPC: add-flow RPC
Tested branch: https://git.opendaylight.org/gerrit/#/c/35118/

What I observed
---------------

I observed that add-flow RPC of the OFP-Li was slow to install flow entries into OpenFlow 1.3 switches.
The rate was 2 flow entries to a switch per second.

In my observation, although the VTN Manager called many add-flow RPC for a switch to install many different flow entries at the same time concurrently, the OFP-Li installed the flow entries at exactly 0.5 second intervals.

For example, the following log messages in karaf.log show that the OFP-Li completed to install flow entries to the switch (openflow:3) at <10:32:11,240>, and <10:32:11,742>, respectively.

2016-02-24 10:32:11,240 (snip) - org.opendaylight.openflowplugin.impl - 0.2.1.SNAPSHOT | flow add finished without error, id=#UF$TABLE*0-35024
2016-02-24 10:32:11,241 (snip) - org.opendaylight.vtn.manager.implementation - 0.4.1.SNAPSHOT | Flow entry has been installed: flow=[id=7f56000000000076-1, pri=10, timeout=(0,0), node=openflow:3, ingress=openflow:3:3, cond=

{DL_SRC=ba:75:46:84:50:34,DL_DST=ea:ed:67:13:85:06,DL_VLAN=0}

, actions=

{OUTPUT(port=openflow:3:1, len=65535)}

2016-02-24 10:32:11,742 (snip) - org.opendaylight.openflowplugin.impl - 0.2.1.SNAPSHOT | flow add finished without error, id=#UF$TABLE*0-35026
2016-02-24 10:32:11,742 (snip) - org.opendaylight.vtn.manager.implementation - 0.4.1.SNAPSHOT | Flow entry has been installed: flow=[id=7f56000000000077-1, pri=10, timeout=(0,0), node=openflow:3, ingress=openflow:3:1, cond=

{DL_SRC=96:99:b7:12:c6:95,DL_DST=ba:75:46:84:50:34,DL_VLAN=0}

, actions=

{OUTPUT(port=openflow:3:3, len=65535)}

The issue is not occurred with the OpenFlow plugin Helium version.