Hi Haim,

Thanks for taking care of this. I see that Miguel has started working on the 
new L2 extension for Flow management。

https://bugs.launchpad.net/neutron/+bug/1563967
https://review.openstack.org/#/c/320439/

We may need to sync up the change with this new work too.

Thanks,
Cathy

From: Haim Daniel [mailto:hdan...@redhat.com]
Sent: Thursday, May 26, 2016 5:42 AM
To: Ihar Hrachyshka
Cc: Cathy Zhang; OpenStack Development Mailing List (not for usage questions); 
Vikram Choudhary; Sean M. Collins; Mathieu Rohon; Shaughnessy, David; 
Eichberger, German; Henry Fourie; Armando M.
Subject: Re: [openstack-dev] [neutron] work on Common Flow Classifier and OVS 
Agent extension for Newton cycle

Hi all,

sorry for digging up this thread. I took a liberty to submitt an RFE per Ihar's 
suggestion for the first step (switching to l2 agent extensions):
https://bugs.launchpad.net/networking-sfc/+bug/1586024

As a followup on that - hoping to send some wip patches in the near time.

Hope to hear your thoughts/suggestions on the $subj.

On Fri, Apr 15, 2016 at 2:44 AM, Ihar Hrachyshka 
<ihrac...@redhat.com<mailto:ihrac...@redhat.com>> wrote:
Cathy Zhang <cathy.h.zh...@huawei.com<mailto:cathy.h.zh...@huawei.com>> wrote:

I think there is no formal spec or anything, just some emails around there.

That said, I don’t follow why it’s a requirement for SFC to switch to l2 agent 
extension mechanism. Even today, with SFC maintaining its own agent, there are 
no clear guarantees for flow priorities that would avoid all possible conflicts.

Cathy> There is no requirement for SFC to switch. My understanding is that 
current L2 agent extension does not solve the conflicting entry issue if two 
features inject the same priority table entry. I think this new L2 agent effort 
is try to come up with a mechanism to resolve this issue. Of course if each 
feature( SFC or Qos) uses its own agent, then there is no coordination and no 
way to avoid conflicts.

Sorry, I probably used misleading wording. I meant, why do we consider the 
semantic flow management support in l2 agent extension framework a 
*prerequisite* for SFC to switch to l2 agent extensions? The existing framework 
should already allow SFC to achieve what you have in the subproject tree 
implemented as a separate agent (essentially a fork of OVS agent). It will also 
set SFC to use standard extension mechanisms instead of hacky inheritance from 
OVS agent classes. So even without the strict semantic flow management, there 
is benefit for the subproject.

With that in mind, I would split this job into 3 pieces:
* first, adopt l2 agent extension mechanism for SFC functionality (dropping 
custom agent);
* then, work on semantic flow management support in OVS agent API class [1];
* once the feature emerges, switch SFC l2 agent extension to the new framework 
to manage SFC flows.

I would at least prioritize the first point and target it to Newton-1. Other 
bullet points may take significant time to bake.

[1] 
https://github.com/openstack/neutron/blob/master/neutron/plugins/ml2/drivers/openvswitch/agent/ovs_agent_extension_api.py

Ihar

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