[v5,0/6] ethdev: introduce Rx buffer split

  The DPDK datapath in the transmit direction is very flexible.
An application can build the multi-segment packet and manages
almost all data aspects - the memory pools where segments
are allocated from, the segment lengths, the memory attributes
like external buffers, registered for DMA, etc.

In the receiving direction, the datapath is much less flexible,
an application can only specify the memory pool to configure the
receiving queue and nothing more. In order to extend receiving
datapath capabilities it is proposed to add the way to provide
extended information how to split the packets being received.

The following structure is introduced to specify the Rx packet
segment:

struct rte_eth_rxseg {
    struct rte_mempool *mp; /* memory pools to allocate segment from */
    uint16_t length; /* segment maximal data length,
		       	configures "split point" */
    uint16_t offset; /* data offset from beginning
		       	of mbuf data buffer */
    uint32_t reserved; /* reserved field */
};

The segment descriptions are added to the rte_eth_rxconf structure:
   rx_seg - pointer the array of segment descriptions, each element
             describes the memory pool, maximal data length, initial
             data offset from the beginning of data buffer in mbuf.
	     This array allows to specify the different settings for
	     each segment in individual fashion.
   n_seg - number of elements in the array

If the extended segment descriptions is provided with these new
fields the mp parameter of the rte_eth_rx_queue_setup must be
specified as NULL to avoid ambiguity.

The new offload flag RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT in device
capabilities is introduced to present the way for PMD to report to
application about supporting Rx packet split to configurable
segments. Prior invoking the rte_eth_rx_queue_setup() routine
application should check RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT flag.

If the Rx queue is configured with new routine the packets being
received will be split into multiple segments pushed to the mbufs
with specified attributes. The PMD will split the received packets
into multiple segments according to the specification in the
description array:

- the first network buffer will be allocated from the memory pool,
  specified in the first segment description element, the second
  network buffer - from the pool in the second segment description
  element and so on. If there is no enough elements to describe
  the buffer for entire packet of maximal length the pool from the
  last valid element will be used to allocate the buffers from for the
  rest of segments

- the offsets from the segment description elements will provide
  the data offset from the buffer beginning except the first mbuf -
  for this one the offset is added to the RTE_PKTMBUF_HEADROOM to get
  actual offset from the buffer beginning. If there is no enough
  elements to describe the buffer for entire packet of maximal length
  the offsets for the rest of segment will be supposed to be zero.

- the data length being received to each segment is limited  by the
  length specified in the segment description element. The data
  receiving starts with filling up the first mbuf data buffer, if the
  specified maximal segment length is reached and there are data
  remaining (packet is longer than buffer in the first mbuf) the
  following data will be pushed to the next segment up to its own
  maximal length. If the first two segments is not enough to store
  all the packet remaining data  the next (third) segment will
  be engaged and so on. If the length in the segment description
  element is zero the actual buffer size will be deduced from
  the appropriate memory pool properties. If there is no enough
  elements to describe the buffer for entire packet of maximal
  length the buffer size will be deduced from the pool of the last
  valid element for the remaining segments.

For example, let's suppose we configured the Rx queue with the
following segments:
    seg0 - pool0, len0=14B, off0=2
    seg1 - pool1, len1=20B, off1=128B
    seg2 - pool2, len2=20B, off2=0B
    seg3 - pool3, len3=512B, off3=0B

The packet 46 bytes long will look like the following:
    seg0 - 14B long @ RTE_PKTMBUF_HEADROOM + 2 in mbuf from pool0
    seg1 - 20B long @ 128 in mbuf from pool1
    seg2 - 12B long @ 0 in mbuf from pool2

The packet 1500 bytes long will look like the following:
    seg0 - 14B @ RTE_PKTMBUF_HEADROOM + 2 in mbuf from pool0
    seg1 - 20B @ 128 in mbuf from pool1
    seg2 - 20B @ 0 in mbuf from pool2
    seg3 - 512B @ 0 in mbuf from pool3
    seg4 - 512B @ 0 in mbuf from pool3
    seg5 - 422B @ 0 in mbuf from pool3

The offload RTE_ETH_RX_OFFLOAD_SCATTER must be present and
configured to support new buffer split feature (if n_seg
is greater than one).

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 with preserving compatibility
with existing API.

Signed-off-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
---
v1: http://patches.dpdk.org/patch/79594/
v2: http://patches.dpdk.org/patch/79893/
    - add feature support to mlx5 PMD

v3: http://patches.dpdk.org/patch/80389/
    - rte_eth_rx_queue_setup_ex is renamed to rte_eth_rxseg_queue_setup
    - DEV_RX_OFFLOAD_BUFFER_SPLIT is renamed to
      RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT
    - commit message update
    - documentaion provided
    - release notes update
    - minor bug fixes in testpmd related part

v4: http://patches.dpdk.org/patch/80401/
    - common part of rx_queue_setup/rxseg_queue_setup

v5: - refactored to approach of providing split configuration
      in the rte_eth_rxconf structure instead of introducing
      the new API routine
    - added support for rxoffs command to testpmd to
      provide segment offsets for complete testing of split
      configurations
    - patchset is split into two parts - PMD part will
      be presented as separate series

Viacheslav Ovsiienko (6):
  ethdev: introduce Rx buffer split
  app/testpmd: add multiple pools per core creation
  app/testpmd: add buffer split offload configuration
  app/testpmd: add rxpkts commands and parameters
  app/testpmd: add rxoffs commands and parameters
  app/testpmd: add extended Rx queue setup

 app/test-pmd/bpf_cmd.c                      |   4 +-
 app/test-pmd/cmdline.c                      | 151 ++++++++++++++++++++++++----
 app/test-pmd/config.c                       | 107 +++++++++++++++++++-
 app/test-pmd/parameters.c                   |  54 ++++++++--
 app/test-pmd/testpmd.c                      | 120 ++++++++++++++++------
 app/test-pmd/testpmd.h                      |  44 ++++++--
 doc/guides/nics/features.rst                |  15 +++
 doc/guides/rel_notes/release_20_11.rst      |   9 ++
 doc/guides/testpmd_app_ug/run_app.rst       |  22 +++-
 doc/guides/testpmd_app_ug/testpmd_funcs.rst |  36 ++++++-
 lib/librte_ethdev/rte_ethdev.c              |  95 +++++++++++++----
 lib/librte_ethdev/rte_ethdev.h              |  58 ++++++++++-
 lib/librte_ethdev/rte_ethdev_version.map    |   1 +
 13 files changed, 621 insertions(+), 95 deletions(-)