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[Eugene Nikanorov <enikanorov@xxxxxxxxxxxx>]

The problem described in the bug seems to be a new feature needed to increase performance on the scale.
It can't be really considered as a bug because the described behavior is as designed.

I suggest to work on this problem in the scope of appropriate blueprint.

** Changed in: neutron
   Importance: Undecided => Medium

** Changed in: neutron
       Status: New => Opinion

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https://bugs.launchpad.net/bugs/1337717

Title:
  L2-population fanout-cast leads to performance and scalability issue

Status in OpenStack Neutron (virtual network service):
  Opinion

Bug description:
  https://github.com/osrg/quantum/blob/master/neutron/plugins/ml2/drivers/l2pop/rpc.py

  def _notification_fanout(self, context, method, fdb_entries):
          ....
          self.fanout_cast(context,
                           self.make_msg(method, fdb_entries=fdb_entries),
                           topic=self.topic_l2pop_update)

  the fanout_cast will publish the message to all L2 agents listening
  "l2population" topic.

  If there are 1000 agents (it is a small cloud), and all of them are
  listening to  "l2population" topic, adding one new port will leads to
  1000 sub messages. Generally rabbitMQ can handle 10k messages per
  second, and the fanout_cast method will leads to greatly performance
  issues, and make the neutron service hard to scale, the concurrency of
  VM port request will be very very small.

  No matter how many ports in the subnet, the performance is up to the
  number of the L2 agents listening the topic.

  The way to solve the performance and scalability issue is to make the
  L2 agent listening a topic related to network, for example, using
  network uuid as the topic. If one port is activated in the subnet,
  only those agents where there are VMs of the same network should
  receive the L2-pop message.  This is parial-mesh, the original design
  purpose, but not implemented yet.

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