[xdp-hints] Re: [RFC net-next v4 2/8] xsk: add TX timestamp and TX checksum offload support

[Jesper Dangaard Brouer <jbrouer@redhat.com>]

On 26/07/2023 01.10, Willem de Bruijn wrote:
> Stanislav Fomichev wrote:
>> On 07/25, Willem de Bruijn wrote:
>>> Stanislav Fomichev wrote:
[...]
>>>> +struct xsk_tx_metadata {
>>>> +	__u32 flags;
>>>> +
>>>> +	/* XDP_TX_METADATA_CHECKSUM */
>>>> +
>>>> +	/* Offset from desc->addr where checksumming should start. */
>>>> +	__u16 csum_start;
>>>> +	/* Offset from csum_start where checksum should be stored. */
>>>> +	__u16 csum_offset;
>>>> +
>>>> +	/* XDP_TX_METADATA_TIMESTAMP */
>>>> +
>>>> +	__u64 tx_timestamp;
>>>> +};
 >>>
>>> Is this structure easily extensible for future offloads,
[...]
> 
> Pacing offload is the other feature that comes to mind. That could
> conceivably use the tx_timestamp field.

I would really like to see hardware offload "pacing" or LaunchTime as
hardware chips i210 and i225 calls it. I looked at the TX descriptor
details for drivers igc (i225) and igb (i210), and documented my finding
here[1], which should help with the code details if someone is motivated
for implementing this (I know of people on xdp-hints list that wanted
this LaunchTime feature).

   [1] 
https://github.com/xdp-project/xdp-project/blob/master/areas/tsn/code01_follow_qdisc_TSN_offload.org#tx-time-to-hardware-driver-igc

AFAIK this patchset uses struct xsk_tx_metadata as both TX and 
TX-Completion, right?.  It would be "conceivable" to reuse tx_timestamp 
field, but it might be confusing for uAPI end-users.  Maybe a union?

--Jesper