Re: [dpdk-dev] [PATCH 0/3] i40e VXLAN TX checksum rework

[Olivier MATZ <olivier.matz@6wind.com>]

Hi Jijiang,

Please find below some comments about the specifications. The global
picture looks fine to me.

I've not reviewed the patch right now, but it's in the pipe.

On 11/27/2014 09:18 AM, Jijiang Liu wrote:
> We have got some feedback about backward compatibility of VXLAN TX checksum offload API with 1G/10G NIC after the i40e VXLAN TX checksum codes were applied, so we have to rework the APIs on i40e, including the changes of mbuf, i40e PMD and csum engine.
>
> The main changes in mbuf are as follows,
> In place of removing PKT_TX_VXLAN_CKSUM, we introducing 2 new flags: PKT_TX_OUT_IP_CKSUM, PKT_TX_UDP_TUNNEL_PKT, and a new field: l4_tun_len.

What about PKT_TX_OUT_UDP_CKSUM instead of PKT_TX_UDP_TUNNEL_PKT? It's
maybe more coherent with the other names.


> Replace the inner_l2_len and the inner_l3_len field with the outer_l2_len and outer_l3_len field.
>
> The existing flags are listed below,
> PKT_TX_IP_CKSUM:     HW IPv4 checksum for non-tunnelling packet/ HW inner IPv4 checksum for tunnelling packet
> PKT_TX_TCP_CKSUM:    HW TCP checksum for non-tunnelling packet/ HW inner TCP checksum for tunnelling packet
> PKT_TX_SCTP_CKSUM:   HW SCTP checksum for non-tunnelling packet/ HW inner SCTP checksum for tunnelling packet
> PKT_TX_UDP_CKSUM:    HW SCTP checksum for non-tunnelling packet/ HW inner SCTP checksum for tunnelling packet
> PKT_TX_IPV4:        IPv4 with no HW checksum offload for non-tunnelling packet/inner IPv4 with no HW checksum offload for tunnelling packet
> PKT_TX_IPV6:        IPv6 non-tunnelling packet/ inner IPv6 with no HW checksum offload for tunnelling packet

As I suggested in the TSO thread, I think the following semantics
is easier to understand for the user:

   - PKT_TX_IP_CKSUM: tell the NIC to compute IP cksum

   - PKT_TX_IPV4: tell the NIC it's an IPv4 packet. Required for L4
     checksum offload or TSO.

   - PKT_TX_IPV6: tell the NIC it's an IPv6 packet. Required for L4
     checksum offload or TSO.

I think it won't make a big difference in the FVL driver.


> let's use a few examples to demonstrate how to use these flags:
> Let say we have a tunnel packet: eth_hdr_out/ipv4_hdr_out/udp_hdr_out/vxlan_hdr/ehtr_hdr_in/ipv4_hdr_in/tcp_hdr_in.There could be several scenarios:
>
> A) User requests HW offload for ipv4_hdr_out checksum.
> He doesn't care is it a tunnelled packet or not.
> So he sets:
>
> mb->l2_len =  eth_hdr_out;
> mb->l3_len = ipv4_hdr_out;
> mb->ol_flags |= PKT_TX_IPV4_CSUM;
>
> B) User is aware that it is a tunnelled packet and requests HW offload for ipv4_hdr_in and tcp_hdr_in *only*.
> He doesn't care about outer IP checksum offload.
> In that case, for FVL  he has 2 choices:
>     1. Treat that packet as a 'proper' tunnelled packet, and fill all the fields:
>       mb->l2_len =  eth_hdr_in;
>       mb->l3_len = ipv4_hdr_in;
>       mb->outer_l2_len = eth_hdr_out;
>       mb->outer_l3_len = ipv4_hdr_out;
>       mb->l4tun_len = vxlan_hdr;
>       mb->ol_flags |= PKT_TX_UDP_TUNNEL_PKT | PKT_TX_IP_CKSUM |  PKT_TX_TCP_CKSUM;
>
>     2. As user doesn't care about outer IP hdr checksum, he can treat everything before ipv4_hdr_in as L2 header.
>     So he knows, that it is a tunnelled packet, but makes HW to treat it as ordinary (non-tunnelled) packet:
>       mb->l2_len = eth_hdr_out + ipv4_hdr_out + udp_hdr_out + vxlan_hdr + ehtr_hdr_in;
>       mb->l3_len = ipv4_hdr_in;
>       mb->ol_flags |= PKT_TX_IP_CKSUM |  PKT_TX_TCP_CKSUM;
>
> i40e PMD will support both B.1 and B.2.
> ixgbe/igb/em PMD supports only B.2.
> if HW supports both - it will be up to user app which method to choose.

I think we should have a flag to advertise outer ip and outer udp
checksum offload support, so the application knows which mode can
be used.


Regards,
Olivier