doc: correct definition of stats per queue feature

[ upstream commit 71eae7f ]

Change the documentation to match current usage of this feature
in the NIC table. Moved this sub heading to be after basic
stats because the queue stats reported now are in the same structure.

Although the "Stats per Queue" feature was originally intended
to be related to stats mapping, the overwhelming majority of drivers
report this feature with a different meaning.

Hopefully in later release the per-queue stats limitations
can be fixed, but this requires and API, ABI, and lots of driver
changes.

Fixes: dad1ec7 ("doc: document NIC features")

Signed-off-by: Stephen Hemminger <[email protected]>
Acked-by: Ferruh Yigit <[email protected]>

doc/guides/nics/features.rst

@@ -688,14 +688,32 @@ Basic stats
 Support basic statistics such as: ipackets, opackets, ibytes, obytes,
 imissed, ierrors, oerrors, rx_nombuf.
 
-And per queue stats: q_ipackets, q_opackets, q_ibytes, q_obytes, q_errors.
-
 These apply to all drivers.
 
 * **[implements] eth_dev_ops**: ``stats_get``, ``stats_reset``.
 * **[related]    API**: ``rte_eth_stats_get``, ``rte_eth_stats_reset()``.
 
 
+.. _nic_features_stats_per_queue:
+
+Stats per queue
+---------------
+
+Supports per queue stats: q_ipackets, q_opackets, q_ibytes, q_obytes, q_errors.
+Statistics only supplied for first ``RTE_ETHDEV_QUEUE_STAT_CNTRS`` (16) queues.
+If driver does not support this feature the per queue stats will be zero.
+
+* **[implements] eth_dev_ops**: ``stats_get``, ``stats_reset``.
+* **[related]    API**: ``rte_eth_stats_get``, ``rte_eth_stats_reset()``.
+
+May also support configuring per-queue stat counter mapping.
+Used by some drivers to workaround HW limitations.
+
+* **[implements] eth_dev_ops**: ``queue_stats_mapping_set``.
+* **[related]    API**: ``rte_eth_dev_set_rx_queue_stats_mapping()``,
+  ``rte_eth_dev_set_tx_queue_stats_mapping()``.
+
+
 .. _nic_features_extended_stats:
 
 Extended stats
@@ -710,18 +728,6 @@ Supports Extended Statistics, changes from driver to driver.
   ``rte_eth_xstats_get_names_by_id()``, ``rte_eth_xstats_get_id_by_name()``.
 
 
-.. _nic_features_stats_per_queue:
-
-Stats per queue
----------------
-
-Supports configuring per-queue stat counter mapping.
-
-* **[implements] eth_dev_ops**: ``queue_stats_mapping_set``.
-* **[related]    API**: ``rte_eth_dev_set_rx_queue_stats_mapping()``,
-  ``rte_eth_dev_set_tx_queue_stats_mapping()``.
-
-
 .. _nic_features_traffic_manager:
 
 Traffic manager