doc: update RSS flow action with best effort

Using the rte_flow action RSS types field,
may result in undefined outcome.

For example selecting both UDP and TCP,
selecting TCP RSS type but the pattern is targeting UDP traffic.
another option is that the PMD doesn't support all requested types.

Until now, it wasn't clear what will happen in such cases.
This commit clarify this issue by stating that the PMD
will work in the best-effort mode, and will fail
in case the requested type is not supported.

Signed-off-by: Ori Kam <orika@nvidia.com>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>

diff --git a/doc/guides/prog_guide/rte_flow.rst b/doc/guides/prog_guide/rte_flow.rst
index 3e5cd1e..119b128 100644 (file)
--- a/doc/guides/prog_guide/rte_flow.rst
+++ b/doc/guides/prog_guide/rte_flow.rst
@@ -1735,6 +1735,19 @@ unspecified "best-effort" settings from the underlying PMD, which depending
 on the flow rule, may result in anything ranging from empty (single queue)
 to all-inclusive RSS.
 
+If non-applicable for matching packets RSS types are requested,
+these RSS types are simply ignored. For example, it happens if:
+
+- Hashing of both TCP and UDP ports is requested
+  (only one can be present in a packet).
+
+- Requested RSS types contradict to flow rule pattern
+  (e.g. pattern has UDP item, but RSS types contain TCP).
+
+If requested RSS hash types are not supported by the Ethernet device at all
+(not reported in ``dev_info.flow_tpe_rss_offloads``),
+the flow creation will fail.
+
 Note: RSS hash result is stored in the ``hash.rss`` mbuf field which
 overlaps ``hash.fdir.lo``. Since `Action: MARK`_ sets the ``hash.fdir.hi``
 field only, both can be requested simultaneously.