netdev - Re: [PATCH net-next v6 3/3] openvswitch: enable NSH support

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Date:   Tue, 5 Sep 2017 19:38:49 +0800
From:   "Yang, Yi" <yi.y.yang@...el.com>
To:     Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "dev@...nvswitch.org" <dev@...nvswitch.org>,
        "jbenc@...hat.com" <jbenc@...hat.com>, "e@...g.me" <e@...g.me>,
        "blp@....org" <blp@....org>,
        "jan.scheurich@...csson.com" <jan.scheurich@...csson.com>
Subject: Re: [PATCH net-next v6 3/3] openvswitch: enable NSH support

On Tue, Sep 05, 2017 at 12:30:09PM +0200, Hannes Frederic Sowa wrote:
> "Yang, Yi" <yi.y.yang@...el.com> writes:
> 
> > I'm not sure what new action you expect to bring here, I think group
> > action is just for this, as you said it isn't only bound to NSH, you can
> > start a new thread to discuss this. I don't think it is in scope of NSH.
> 
> It is in scope of this discussion as you will provide a user space API
> that makes the NSH context fields accessible from user space in a
> certain way. If you commit to this, there is no way going back.

We can change this later if we really find a better way to handle this
because it isn't defined in include/uapi/linux/openvswitch.h, so I still
have backdoor to do this if needed :-)

> 
> I haven't yet grasped the idea on how those fields will be used in OVS
> besides load balancing. Even for load balancing the tunnel itself
> (vxlan-gpe + UDP source port or ipv6 flowlabel) already provides enough
> entropy to do per-flow load balancing. What else is needed?  Why a
> context header for that? You just need multiple action chains and pick
> one randomly.

For our sfc use case in Opendaylight, we use context[0] for tunnel ID,
context[1] for destination IP for reverse RSP, they are used to match
and set in OpenFlow table, you can't limit users to use them in such
ways.

If you check GENEVE implementation, tun_metadata* can be set or matched
as any other match field.

Actually the most important information in NSH are just these context
headers, you can't limit imagination of users by removing them from flow
keys.

My point is to bring miniflow into kernel data path to fix your concern,
this will benefit your employer directly :-)

I'm just curious your company has hardware to offload NSH? Which
company are you from?

> 
> The only protocol that I can compare that to is geneve with TLVs, but
> the TLVs are global and uniquie and a property of the networking
> forwarding backplane and not a property of the path inside a tenant. So
> I expect this actually to be the first case where I think that matters.
> 
> Why are context labels that special that they are not part of tun_ops?
> 
> Thanks,
> Hannes