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

[Viacheslav Ovsiienko <viacheslavo@mellanox.com>]

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 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