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

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

Hi Oliver,

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Olivier MATZ
> Sent: Thursday, November 27, 2014 9:45 AM
> To: Liu, Jijiang; dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH 0/3] i40e VXLAN TX checksum rework
> 
> 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.

FVL HW don't support outer L4 checksum offload.
But to calculate inner checksums correctly, it needs a hint from SW about L4 Tunnelling Type.

> 
> 
> > 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.

No, no big difference here, but I still think it will be a bit cleaner if all 3 flags would be nutually exclusive.
In fact,  we can unite all 3 of them them into 2 bits,    same as we doing for L4 checksum flags.

> 
> 
> > 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.

You mean a new DEV_TX_OFFLOAD_* value, right?
Something like:  DEV_TX_OFFLOAD_UDP_TUNNEL?
And make i40e_dev_info_get() to return it?
Yes, forgot about it, sounds like a proper thing to do. 

Konstantin

> 
> 
> Regards,
> Olivier