net/mlx5: add Multi-Packet Rx support

Multi-Packet Rx Queue (MPRQ a.k.a Striding RQ) can further save PCIe
bandwidth by posting a single large buffer for multiple packets. Instead of
posting a buffer per a packet, one large buffer is posted in order to
receive multiple packets on the buffer. A MPRQ buffer consists of multiple
fixed-size strides and each stride receives one packet.

Rx packet is mem-copied to a user-provided mbuf if the size of Rx packet is
comparatively small, or PMD attaches the Rx packet to the mbuf by external
buffer attachment - rte_pktmbuf_attach_extbuf(). A mempool for external
buffers will be allocated and managed by PMD.

Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
Acked-by: Shahaf Shuler <shahafs@mellanox.com>

1 files changed, 58 insertions, 0 deletions

diff --git a/doc/guides/nics/mlx5.rst b/doc/guides/nics/mlx5.rst
index 13cc3f8..a7d5c90 100644
--- a/doc/guides/nics/mlx5.rst
+++ b/doc/guides/nics/mlx5.rst
@@ -105,10 +105,14 @@ Limitations
 - A multi segment packet must have less than 6 segments in case the Tx burst function
   is set to multi-packet send or Enhanced multi-packet send. Otherwise it must have
   less than 50 segments.
+
 - Count action for RTE flow is **only supported in Mellanox OFED**.
+
 - Flows with a VXLAN Network Identifier equal (or ends to be equal)
   to 0 are not supported.
+
 - VXLAN TSO and checksum offloads are not supported on VM.
+
 - VF: flow rules created on VF devices can only match traffic targeted at the
   configured MAC addresses (see ``rte_eth_dev_mac_addr_add()``).
 
@@ -119,6 +123,13 @@ Limitations
    the device. In case of ungraceful program termination, some entries may
    remain present and should be removed manually by other means.
 
+- When Multi-Packet Rx queue is configured (``mprq_en``), a Rx packet can be
+  externally attached to a user-provided mbuf with having EXT_ATTACHED_MBUF in
+  ol_flags. As the mempool for the external buffer is managed by PMD, all the
+  Rx mbufs must be freed before the device is closed. Otherwise, the mempool of
+  the external buffers will be freed by PMD and the application which still
+  holds the external buffers may be corrupted.
+
 Statistics
 ----------
 
@@ -229,6 +240,53 @@ Run-time configuration
   - x86_64 with ConnectX-4, ConnectX-4 LX and ConnectX-5.
   - POWER8 and ARMv8 with ConnectX-4 LX and ConnectX-5.
 
+- ``mprq_en`` parameter [int]
+
+  A nonzero value enables configuring Multi-Packet Rx queues. Rx queue is
+  configured as Multi-Packet RQ if the total number of Rx queues is
+  ``rxqs_min_mprq`` or more and Rx scatter isn't configured. Disabled by
+  default.
+
+  Multi-Packet Rx Queue (MPRQ a.k.a Striding RQ) can further save PCIe bandwidth
+  by posting a single large buffer for multiple packets. Instead of posting a
+  buffers per a packet, one large buffer is posted in order to receive multiple
+  packets on the buffer. A MPRQ buffer consists of multiple fixed-size strides
+  and each stride receives one packet. MPRQ can improve throughput for
+  small-packet tarffic.
+
+  When MPRQ is enabled, max_rx_pkt_len can be larger than the size of
+  user-provided mbuf even if DEV_RX_OFFLOAD_SCATTER isn't enabled. PMD will
+  configure large stride size enough to accommodate max_rx_pkt_len as long as
+  device allows. Note that this can waste system memory compared to enabling Rx
+  scatter and multi-segment packet.
+
+- ``mprq_log_stride_num`` parameter [int]
+
+  Log 2 of the number of strides for Multi-Packet Rx queue. Configuring more
+  strides can reduce PCIe tarffic further. If configured value is not in the
+  range of device capability, the default value will be set with a warning
+  message. The default value is 4 which is 16 strides per a buffer, valid only
+  if ``mprq_en`` is set.
+
+  The size of Rx queue should be bigger than the number of strides.
+
+- ``mprq_max_memcpy_len`` parameter [int]
+
+  The maximum length of packet to memcpy in case of Multi-Packet Rx queue. Rx
+  packet is mem-copied to a user-provided mbuf if the size of Rx packet is less
+  than or equal to this parameter. Otherwise, PMD will attach the Rx packet to
+  the mbuf by external buffer attachment - ``rte_pktmbuf_attach_extbuf()``.
+  A mempool for external buffers will be allocated and managed by PMD. If Rx
+  packet is externally attached, ol_flags field of the mbuf will have
+  EXT_ATTACHED_MBUF and this flag must be preserved. ``RTE_MBUF_HAS_EXTBUF()``
+  checks the flag. The default value is 128, valid only if ``mprq_en`` is set.
+
+- ``rxqs_min_mprq`` parameter [int]
+
+  Configure Rx queues as Multi-Packet RQ if the total number of Rx queues is
+  greater or equal to this value. The default value is 12, valid only if
+  ``mprq_en`` is set.
+
 - ``txq_inline`` parameter [int]
 
   Amount of data to be inlined during TX operations. Improves latency.