doc: add Tx inline hint in mlx5 guide

The no-inline hint flag is described.

Fixes: cacb44a09962 ("net/mlx5: add no-inline Tx flag")

Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>

diff --git a/doc/guides/nics/mlx5.rst b/doc/guides/nics/mlx5.rst
index 4a96979..afd11cd 100644 (file)
--- a/doc/guides/nics/mlx5.rst
+++ b/doc/guides/nics/mlx5.rst
@@ -97,6 +97,7 @@ Features
   increment/decrement, count, drop, mark. For details please see :ref:`mlx5_offloads_support`.
 - Flow insertion rate of more then million flows per second, when using Direct Rules.
 - Support for multiple rte_flow groups.
+- Per packet no-inline hint flag to disable packet data copying into Tx descriptors.
 - Hardware LRO.
 
 Limitations
@@ -189,6 +190,33 @@ Limitations
   To receive IPv6 Multicast messages on VM, explicitly set the relevant
   MAC address using rte_eth_dev_mac_addr_add() API.
 
+- To support a mixed traffic pattern (some buffers from local host memory, some
+  buffers from other devices) with high bandwidth, a mbuf flag is used.
+
+  An application hints the PMD whether or not it should try to inline the
+  given mbuf data buffer. PMD should do the best effort to act upon this request.
+
+  The hint flag ``RTE_PMD_MLX5_FINE_GRANULARITY_INLINE`` is dynamic,
+  registered by application with rte_mbuf_dynflag_register(). This flag is
+  purely driver-specific and declared in PMD specific header ``rte_pmd_mlx5.h``,
+  which is intended to be used by the application.
+
+  To query the supported specific flags in runtime,
+  the function ``rte_pmd_mlx5_get_dyn_flag_names`` returns the array of
+  currently (over present hardware and configuration) supported specific flags.
+  The "not inline hint" feature operating flow is the following one:
+
+    - application starts
+    - probe the devices, ports are created
+    - query the port capabilities
+    - if port supporting the feature is found
+    - register dynamic flag ``RTE_PMD_MLX5_FINE_GRANULARITY_INLINE``
+    - application starts the ports
+    - on ``dev_start()`` PMD checks whether the feature flag is registered and
+      enables the feature support in datapath
+    - application might set the registered flag bit in ``ol_flags`` field
+      of mbuf being sent and PMD will handle ones appropriately.
+
 - The amount of descriptors in Tx queue may be limited by data inline settings.
   Inline data require the more descriptor building blocks and overall block
   amount may exceed the hardware supported limits. The application should