Re: [PATCH net-next,RFC 00/13] New fast forwarding path

On Thu, Jun 14, 2018 at 11:50:49AM -0400, Willem de Bruijn wrote:

quoted

This patchset supports both layer 3 IPv4 and IPv6, and layer 4 TCP and
UDP protocols. This fastpath also integrates with the IPSec
infrastructure and the ESP protocol.

We have collected performance numbers:

        TCP TSO         TCP Fast Forward
        32.5 Gbps       35.6 Gbps

        UDP             UDP Fast Forward
        17.6 Gbps       35.6 Gbps

        ESP             ESP Fast Forward
        6 Gbps          7.5 Gbps

For UDP, this is doubling performance, and we almost achieve line rate
with one single CPU using the Intel i40e NIC. We got similar numbers
with the Mellanox ConnectX-4. For TCP, this is slightly improving things
even if TSO is being defeated given that we need to segment the packet
chain in software.

The difference between TCP and UDP stems from lack of GRO for UDP.

Right.

We
recently added UDP GSO to allow for batch traversal of the UDP stack on
transmission. Adding a UDP GRO handler can probably extend batching to
the forwarding path in a similar way without the need for a new infrastructure.

That's more or less what we did. The batching method ist just
optimized for the forwarding path. We are generating skb chains
by chaning at the frag_list pointer of the first skb. With that,
we don't need to mange packet. We keep the packets in the native
form, so the 'segmentation' is rather easy.

The rest is just to be able to configure this and to make
sure that we handle only flows that are going to be (fast)
forwarded, as the upper stack can not (yet) handle such
skb chains.