populate fdb entries before spawning vm

[Perry]

before spawning vm, neutron l2 agent has to wire up device on compute. This is controlled by provisioning_block in neutron. However L2 agent on compute takes much time to sync lots of fdb info during wire up device and which causes VM takes long time to spawn and active. The fdb synchronization could be done when spawning vm to improve the performance of booting vm. This also delays next loop of daemon_loop to get another new taps processed.

Steps to re-produce the problem:

L2 of linuxbridge and dedicated compute nodes

1) nova boot --image ubuntu-guest-image-14.04 --flavor m1.medium --nic net-name=internal --security-groups unlocked --min-count 50 --max-count 50 free_deletable

2)observe numerous log as below in neutron-linuxbridge-agent.log.

2017-03-07 05:01:43.220 25336 DEBUG neutron.agent.linux.utils [req-534e9f59-0a66-4071-8c40-977f87a6be49 - - - - -] Running command: ['sudo', '/bin/neutron-rootwrap', '/etc/neutron/rootwrap.conf', 'bridge', 'fdb', 'append', '00:00:00:00:00:00', 'dev', 'vxlan-1', 'dst', '10.160.152.141'] create_process /usr/lib/python2.7/site-packages/neutron/agent/linux/utils.py:89

3)eventually, it takes lots of time to process new tap (6.2 seconds) in neutron-linuxbridge-agent.log

2017-03-07 05:01:44.654 25336 DEBUG neutron.plugins.ml2.drivers.agent._common_agent [req-835dd509-27b0-42e3-903d-32577187d288 - - - - -] Loop iteration exceeded interval (2 vs. 6.2001709938)! daemon_loop /usr/lib/python2.7/site-packages/neutron/plugins/ml2/drivers/agent/_common_agent.py:466

[Kevin Benton (kevinbenton)]

Yes, with the l2pop operations currently inside of the device retrieval, this can become slow. I would like to revisit this after we have switched to push notifications for the l2 agent because it will change these interactions quite a bit.