[dpdk-dev] question regarding rx checksum offload flags

Olivier Matz olivier.matz at 6wind.com
Thu Sep 17 16:05:03 CEST 2020


Hi Lance,

On Mon, Aug 24, 2020 at 04:11:45PM -0400, Lance Richardson wrote:
> I was looking for some clarification regarding how rx checksum
> flags should be set for tunnel packets having both inner and outer
> IP/L4 headers.
> 
> Based on comments in rte_mbuf_core.h, it seems to me. that the
> inner (encapsulated) IP header checksum status should determine
> which of these goes into ol_flags:
>     PKT_RX_IP_CKSUM_UNKNOWN
>     PKT_RX_IP_CKSUM_BAD
>     PKT_RX_IP_CKSUM_GOOD
>     PKT_RX_IP_CKSUM_NONE
> 
> Similarly, the L4 checksum status should determine which of these
> goes into ol_flags:
>    PKT_RX_L4_CKSUM_UNKNOWN
>    PKT_RX_L4_CKSUM_BAD
>    PKT_RX_L4_CKSUM_GOOD
>    PKT_RX_L4_CKSUM_NONE
> 
> The IP header checksum status for the outer IP header should determine
> whether this flag is set in ol_flags:
>     PKT_RX_EIP_CKSUM_BAD
> 
> And for UDP-based tunnel encapsulations, the outer L4 checksum status
> should determine which of these goes into ol_flags:
>     PKT_RX_OUTER_L4_CKSUM_UNKNOWN
>     PKT_RX_OUTER_L4_CKSUM_BAD
>     PKT_RX_OUTER_L4_CKSUM_GOOD
>     PKT_RX_OUTER_L4_CKSUM_INVALID
> 
> Finally, the checksum status of inner headers should have no influence
> on PKT_RX_EIP_CKSUM_BAD or PKT_RX_OUTER_L4_CKSUM_*, and
> likewise the checksum status of outer headers should have no influence
> on PKT_RX_L4_CKSUM_* or PKT_RX_IP_CKSUM_*.
> 
> Is this correct? Apologies for such a basic question, but I'm having trouble
> correlating the above with implementations.
> 
> Thanks and regards,
>     Lance

The PKT_RX_EIP_CKSUM_BAD flag was added by these commits:

https://git.dpdk.org/dpdk/commit/?id=c22265f6fd4cdcac9ee1b4970e4af8459d267516
https://git.dpdk.org/dpdk/commit/?id=d909af8f72ca3f8ab4fe1942abfb4f53e15ff8bc

First, to be honnest, I don't think this API is the right one. From a software
stack point of view, it would have been more logical to have PKT_RX_INNER_*
flags instead of outer.

That said, your understanding looks correct to me. I think this is the
expected behavior when the DEV_RX_OFFLOAD_OUTER* capability is enabled.

If the capability is not set, only the PKT_RX_IP_CKSUM* and
PKT_RX_L4_CKSUM* flags may be set, and they reference the first layer.

Regards,
Olivier


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