Re: XDP seeking input from NIC hardware vendors

Alexei Starovoitov via iovisor-dev
2016-07-08T02:22:12Z

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.