Description of problem:

We need the following Liberty neutron patches ported to the Red Hat’s OSP8 for scalability reason.  Without the must have patch, we cannot scale more than 25+ VMs at a time on the same compute reliably.

Must have
=========
https://review.openstack.org/#/c/293286/

Good to have
===========
https://review.openstack.org/#/c/271804/
https://review.openstack.org/#/c/280092/

We have tested the must have patch by itself and along with the good to have patches, both scenarios we were able to increase performance.


Version-Release number of selected component (if applicable):

openstack-neutron.noarch     1:7.0.1-15.el7ost
openstack-neutron-ml2.noarch 1:7.0.1-15.el7ost


How reproducible:

Using OpenStack Rally running nova_boot scenario multiple times

Steps to Reproduce:

1. Bring up a working Liberty OpenStack cloud with two computes
2. Install OpenStack Rally
3. Upload the cirros image
4. Run the "./rally/samples/tasks/scenarios/nova/boot.json" scenario with the following modification
{
   "NovaServers.boot_server": [
        {
            "args": {
                "flavor": {
                    "name": "ram64"
                },
                "image": {
                    "name": "^cirros-0.3.4-x86_64.*"
                },
                "auto_assign_nic" : true    <=== enable networking
            },
            "runner": {
                "type": "constant",
                "times": 50,         <=== increased from 10 to 50
                "concurrency": 5     <=== increased from 2 to 5
            },
            "context": {
                "users": {
                    "tenants": 1,
                    "users_per_tenant": 1
                },
                "network": {
                    "start_cidr": "10.0.0.0/16"
                },
                "flavors": [
                    {
                        "name": "ram64",
                        "ram": 64
                    }
                ],
                "quotas" : {
                    "nova": {
                         "instances" : -1,
                         "cores" : -1,
                         "ram" : -1,
                         "metadata_items" : -1
                    },
                    "neutron" : {
                        "network" : -1,
                        "subnet" : -1,
                        "port" : -1,
                        "router" : -1,
                        "floatingip" : -1,
                        "security_group" : -1,
                        "security_group_rule": -1
                    }
                }
            }
        }
   ]
}

5. First run will be fast, nova boot time is around ~15-20 seconds
6. Repeat the same test few more times, each time the nova boot time will start to degrade to over time
7. Eventually the boot time will be over 60 seconds which is the vif_plugging_timeout value
 

Actual results:

neutron-server.log
===================
<..snip..>
2016-05-10 19:21:32.736 38 ERROR neutron.notifiers.nova [-] Failed to notify nova on events: [{'status': 'completed', 'tag': u'1698baa3-9fe0-4539-ba48-1eb4f5683b8d', 'name': 'network-vif-plugged', 'server_uuid': u'e3f13bb1-da01-4337-abf6-ad672461de2a'}]
<..snip..>

VM timeout waiting for network and metadata service


Expected results:

Should not observed the above error message and VM should be able to boot successfully with DHCP address.


Additional info: