Re: [dpdk-dev] [PATCH] doc: announce changes to ethdev rxconf structure

[Jerin Jacob <jerinjacobk@gmail.com>]

On Mon, Aug 3, 2020 at 4:28 PM Viacheslav Ovsiienko
<viacheslavo@mellanox.com> wrote:
>
> The DPDK datapath in the transmit direction is very flexible.
> The applications can build multisegment packets and manages
> almost all data aspects - the memory pools where segments
> are allocated from, the segment lengths, the memory attributes
> like external, registered, etc.
>
> In the receiving direction, the datapath is much less flexible,
> the applications can only specify the memory pool to configure
> the receiving queue and nothing more. In order to extend the
> receiving datapath capabilities it is proposed to add the new
> fields into rte_eth_rxconf structure:
>
> struct rte_eth_rxconf {
>     ...
>     uint16_t rx_split_num; /* number of segments to split */
>     uint16_t *rx_split_len; /* array of segment lengthes */
>     struct rte_mempool **mp; /* array of segment memory pools */

The pool has the packet length it's been configured for.
So I think, rx_split_len can be removed.

This feature also available in Marvell HW. So it not specific to one vendor.
Maybe we could just the use case mention the use case in the depreciation notice
and the tentative change in rte_eth_rxconf and exact details can be worked
out at the time of implementation.

With the above change:
Acked-by: Jerin Jacob <jerinj@marvell.com>


>     ...
> };
>
> The non-zero value of rx_split_num field configures the receiving
> queue to split ingress packets into multiple segments to the mbufs
> allocated from various memory pools according to the specified
> lengths. The zero value of rx_split_num field provides the
> backward compatibility and queue should be configured in a regular
> way (with single/multiple mbufs of the same data buffer length
> allocated from the single memory pool).
>
> The new approach would allow splitting the ingress packets into
> multiple parts pushed to the memory with different attributes.
> For example, the packet headers can be pushed to the embedded data
> buffers within mbufs and the application data into the external
> buffers attached to mbufs allocated from the different memory
> pools. The memory attributes for the split parts may differ
> either - for example the application data may be pushed into
> the external memory located on the dedicated physical device,
> say GPU or NVMe. This would improve the DPDK receiving datapath
> flexibility preserving compatibility with existing API.
>
> Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
> ---
>  doc/guides/rel_notes/deprecation.rst | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
> index ea4cfa7..cd700ae 100644
> --- a/doc/guides/rel_notes/deprecation.rst
> +++ b/doc/guides/rel_notes/deprecation.rst
> @@ -99,6 +99,11 @@ Deprecation Notices
>    In 19.11 PMDs will still update the field even when the offload is not
>    enabled.
>
> +* ethdev: add new fields to ``rte_eth_rxconf`` to configure the receiving
> +  queues to split ingress packets into multiple segments according to the
> +  specified lengths into the buffers allocated from the specified
> +  memory pools. The backward compatibility to existing API is preserved.
> +
>  * ethdev: ``rx_descriptor_done`` dev_ops and ``rte_eth_rx_descriptor_done``
>    will be deprecated in 20.11 and will be removed in 21.11.
>    Existing ``rte_eth_rx_descriptor_status`` and ``rte_eth_tx_descriptor_status``
> --
> 1.8.3.1
>