Changing of_interface between native and ovs-ofctl causes packet drops

[Akihiro Motoki]

When I change [ovs] of_interface option from ovs-ofctl to native, ping packets are dropped when restarting ovs-agent.

https://review.openstack.org/#/c/599496/ tries to drop of_interface option.
This means if a deployer uses of_interface "ovs-ofctl" packet drops always occur regardless of their intention.

I am not sure this packet drop is the expected behavior when changing of_interface option.

I confirmed this behavior with the neutron master (stein).
commit 317cdbf40850964080a0a30d6212a3b536df1caa

Note that the similar packet loss is observed when I changed of_interface from native to ovs-ofctl, but I think this is less important.

Steps to reproduce:

(1) Create a server and associate a FIP to the server
(2) Allow PING to the server
(3) Set[ovs] of_interface option to "ovs-ofctl" and run "sudo service devstack@neutron-agent restart" to ensure of_interface is "ovs-ofctl"
(4) Start ping to the server like "ping 172.24.4.3 -i 0.2" (172.24.4.3 is the FIP)
(5) Set[ovs] of_interface option to "native" and run "sudo service devstack@neutron-agent restart" to ensure of_interface is "native"
(6) Wait for 10 or some seconds (to ensure OVS flows are repopulated)
(7) Stop ping and check if a packet loss occurs

Result:
http://paste.openstack.org/show/730374/
115 packets transmitted, 108 received, 6% packet loss, time 22843ms

[IWAMOTO Toshihiro (iwamoto)]

I'll have a look to see if it can be dealt with.

[IWAMOTO Toshihiro (iwamoto)]

ovs friendly clears up flows when a controller is set up.
See ovs/ofproto/connmgr.c:connmgr_set_controllers.

Dealing with this on the OpenStack side can be impossible.

[Hongbin Lu (hongbin.lu)]

I can confirm that packet loss occurred by following the reproducing steps, but not sure if neutron should deal with it as @IWAMOTO Toshihiro mentioned.

[OpenStack Infra (hudson-openstack)]

Related fix proposed to branch: master
Review: https://review.openstack.org/604228

[OpenStack Infra (hudson-openstack)]

Change abandoned by Slawek Kaplonski (<email address hidden>) on branch: master
Review: https://review.opendev.org/604228
Reason: This review is > 4 weeks without comment and currently blocked by a core reviewer with a -2. We are abandoning this for now. Feel free to reactivate the review by pressing the restore button and contacting the reviewer with the -2 on this review to ensure you address their concerns.

[Brian Haley (brian-haley)]

The of_interface config option has been removed and only the native driver is supported now, so closing this bug.