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

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Message-ID: <CAADnVQKhUAR=qVg9q82ngYMzQnoDVbq+wupzdMrH8WiCeMiU4A@mail.gmail.com>
Date:	Mon, 22 Sep 2014 18:54:29 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	Thomas Graf <tgraf@...g.ch>, Jiri Pirko <jiri@...nulli.us>,
	John Fastabend <john.r.fastabend@...el.com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Neil Horman <nhorman@...driver.com>,
	Andy Gospodarek <andy@...yhouse.net>,
	Daniel Borkmann <dborkman@...hat.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Jesse Gross <jesse@...ira.com>,
	Pravin Shelar <pshelar@...ira.com>,
	Andy Zhou <azhou@...ira.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	Vladislav Yasevich <vyasevic@...hat.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Scott Feldman <sfeldma@...ulusnetworks.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Roopa Prabhu <roopa@...ulusnetworks.com>,
	John Linville <linville@...driver.com>,
	"dev@...nvswitch.org" <dev@...nvswitch.org>,
	Jason Wang <jasowang@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	ryazanov.s.a@...il.com, Lennert Buytenhek <buytenh@...tstofly.org>,
	aviadr@...lanox.com, Felix Fietkau <nbd@...nwrt.org>,
	Neil Jerram <Neil.Jerram@...aswitch.com>, ronye@...lanox.com,
	simon.horman@...ronome.com,
	Alexander Duyck <alexander.h.duyck@...el.com>
Subject: Re: [patch net-next v2 8/9] switchdev: introduce Netlink API

On Mon, Sep 22, 2014 at 8:10 AM, Tom Herbert <therbert@...gle.com> wrote:
> On Mon, Sep 22, 2014 at 1:13 AM, Thomas Graf <tgraf@...g.ch> wrote:
>> On 09/20/14 at 03:50pm, Alexei Starovoitov wrote:
>>> I think HW should not be limited by SW abstractions whether
>>> these abstractions are called flows, n-tuples, bridge or else.
>>> Really looking forward to see "device reporting the headers as
>>> header fields (len, offset) and the associated parse graph"
>>> as the first step.
>>>
>>> Another topic that this discussion didn't cover yet is how this
>>> all connects to tunnels and what is 'tunnel offloading'.

> encapsulation (stuffing a few bytes of header into a packet) is in
> itself not nearly an expensive enough operation to warrant offloading
> to the NIC. Personally, I wish if NIC vendors are going to focus on

On contrary, generic tunneling is most important one to get right
when we're talking offloads.
Adding encap header is easy to do in hw, but it breaks all other
offloads if hw is not generic. Consider gso packet coming from vm.
Generic tunnel allows sw to add inner headers, outer headers and
setup offload offsets, so that HW does segmentation, checksuming
of inner packet, adjusts inner headers and adds final outer encap.
And this is just tx offload. On rx smart tunnel offload in HW parses
encap and goes all the way to inner headers to verify checksums,
it also steers based on inner headers.
Try mellanox nics with and without vxlan offload to see
the difference.
It looks like fm10k will be just as good, but existing encaps are
not going to last forever, so RX should be improved they way John
is saying. There gotta to be a 'parse graph' for HW to see past
variable length encap and into inner headers.
checksum_complete style of offloading checksum verification
is not efficient. The cost of adjusting it over and over while
parsing encaps is too high. Plus cpu steering based on outer
headers is just too slow when speeds are in 40G range.

> stateful offload I rather see it be for encryption which I believe
> currently does warrant offload at 40G and higher speeds.

encryption offload is badly needed as well. Unfortunately it's
not seen as nic feature yet.
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