netdev - Re: XDP seeking input from NIC hardware vendors

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Message-ID: <20160708022210.GA12244@ast-mbp.thefacebook.com>
Date:	Thu, 7 Jul 2016 19:22:12 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	"Fastabend, John R" <john.r.fastabend@...el.com>
Cc:	Jesper Dangaard Brouer <brouer@...hat.com>,
	"iovisor-dev@...ts.iovisor.org" <iovisor-dev@...ts.iovisor.org>,
	Brenden Blanco <bblanco@...mgrid.com>,
	Rana Shahout <ranas@...lanox.com>, Ari Saha <as754m@....com>,
	Tariq Toukan <tariqt@...lanox.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Simon Horman <horms@...ge.net.au>,
	Simon Horman <simon.horman@...ronome.com>,
	Jakub Kicinski <jakub.kicinski@...ronome.com>,
	Edward Cree <ecree@...arflare.com>
Subject: Re: XDP seeking input from NIC hardware vendors

On Thu, Jul 07, 2016 at 03:18:11PM +0000, Fastabend, John R wrote:
> Hi Jesper,
> 
> I have done some previous work on proprietary systems where we used hardware to do the classification/parsing then passed a cookie to the software which used the cookie to lookup a program to run on the packet. When your programs are structured as a bunch of parsing followed by some actions this can provide real performance benefits. Also a lot of existing hardware supports this today assuming you use headers the hardware "knows" about. It's a natural model for hardware that uses a parser followed by tcam/cam/sram/etc lookup tables.

looking at bpf programs written in plumgrid, facebook and cisco
with full certainty I can assure that parse/action split doesn't exist.
Parsing is always interleaved with lookups and actions.
cpu spends a tiny fraction of time doing parsing. Lookups are the heaviest.
Trying to split single logical program into parsing/after_parse stages
has no pracitcal benefit.

> If the goal is to just separate XDP traffic from non-XDP traffic you could accomplish this with a combination of SR-IOV/macvlan to separate the device queues into multiple netdevs and then run XDP on just one of the netdevs. Then use flow director (ethtool) or 'tc cls_u32/flower' to steer traffic to the netdev. This is how we support multiple networking stacks on one device by the way it is called the bifurcated driver. Its not too far of a stretch to think we could offload some simple XDP programs to program the splitting of traffic instead of cls_u32/flower/flow_director and then you would have a stack of XDP programs. One running in hardware and a set running on the queues in software.

the above sounds like much better approach then Jesper/mine prog_per_ring stuff.
If we can split the nic via sriov and have dedicated netdev via VF just for XDP that's way cleaner approach.
I guess we won't need to do xdp_rxqmask after all.