netdev - Re: [patch net-next v2 8/9] switchdev: introduce Netlink API

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Date:	Sat, 20 Sep 2014 12:51:40 +0100
From:	Thomas Graf <tgraf@...g.ch>
To:	Jamal Hadi Salim <jhs@...atatu.com>
Cc:	Jiri Pirko <jiri@...nulli.us>,
	John Fastabend <john.r.fastabend@...el.com>,
	netdev@...r.kernel.org, davem@...emloft.net, nhorman@...driver.com,
	andy@...yhouse.net, dborkman@...hat.com, ogerlitz@...lanox.com,
	jesse@...ira.com, pshelar@...ira.com, azhou@...ira.com,
	ben@...adent.org.uk, stephen@...workplumber.org,
	jeffrey.t.kirsher@...el.com, vyasevic@...hat.com,
	xiyou.wangcong@...il.com, edumazet@...gle.com,
	sfeldma@...ulusnetworks.com, f.fainelli@...il.com,
	roopa@...ulusnetworks.com, linville@...driver.com,
	dev@...nvswitch.org, jasowang@...hat.com, ebiederm@...ssion.com,
	nicolas.dichtel@...nd.com, ryazanov.s.a@...il.com,
	buytenh@...tstofly.org, aviadr@...lanox.com, nbd@...nwrt.org,
	alexei.starovoitov@...il.com, Neil.Jerram@...aswitch.com,
	ronye@...lanox.com, simon.horman@...ronome.com,
	alexander.h.duyck@...el.com
Subject: Re: [patch net-next v2 8/9] switchdev: introduce Netlink API

On 09/20/14 at 07:32am, Jamal Hadi Salim wrote:
> I am sorry to have tied the two together. Maybe not OVS but the approach
> described is heaven for vendor SDKs.

I fail to see the connection. You can use switch vendor SDK no matter
how we define the kernel APIs. They already exist and have been
designed in a way to be completely indepenedent from the kernel.

Are you referring to vendor specific decisions in user space in
general? I believe that the whole point of swdev is to provide *that*
level of abstraction so decisions can be made in a vendor neutral way.

> >The statement was that the requirement of deriving hardware flows from
> >software flows *in the kernel* is not flexible enough for the future
> >for reasons such as:
> >
> >1) The OVS software data path might be based on eBPF in the future and
> >    it is unclear how we could derive hardware flows from that
> >    transparently.
> >
> 
> Who says you cant put BPF in hardware?

I don't think anybody is saying that. P4 is likely a reality soon. But
we definitely want hardware offload in a BPF world even if the hardware
can't do BPF yet.

> And why is OVS defining how BPF should evolve or how it should be used?

Not sure I understand. OVS would be a user of eBPF just like tracing,
xt_BPF, socket filter, ...

> >2) Depending on hardware capabilities. Hardware flows might need to be
> >    assisted by software flow counterparts and it is believed that it
> >    is the wrong approach to push all the necessary context for the
> >    decision down into the kernel. This can be argued about and I don't
> >    feel strongly either way.
> >
> 
> Pointing to the current FDB offload: You can select to bypass
> and not use s/ware.

As I said, this can be argued about. It would require to push a lot of
context into the kernel though. The FDB offload is relatively trivial
in comparison to the complexity OVS user space can handle. I can't think
of any reasons why to complicate the kernel further with OVS specific
knowledge as long as we can guarantee the vendor abstraction.
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