.. BSD LICENSE
- Copyright(c) 2010-2014 Intel Corporation. All rights reserved.
+ Copyright(c) 2010-2015 Intel Corporation. All rights reserved.
All rights reserved.
Redistribution and use in source and binary forms, with or without
Refer to the testpmd source code for details.
Also, L4 (UDP/TCP/ SCTP) checksum offload by the NIC can be enabled for an individual packet as long as the packet mbuf is set up correctly. See `Hardware Offload`_ for details.
-Configuration of Transmit and Receive Queues
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Configuration of Transmit Queues
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Each transmit queue is independently configured with the following information:
When configuring for DCB operation, at port initialization, both the number of transmit queues and the number of receive queues must be set to 128.
+Free Tx mbuf on Demand
+~~~~~~~~~~~~~~~~~~~~~~
+
+Many of the drivers do not release the mbuf back to the mempool, or local cache,
+immediately after the packet has been transmitted.
+Instead, they leave the mbuf in their Tx ring and
+either perform a bulk release when the ``tx_rs_thresh`` has been crossed
+or free the mbuf when a slot in the Tx ring is needed.
+
+An application can request the driver to release used mbufs with the ``rte_eth_tx_done_cleanup()`` API.
+This API requests the driver to release mbufs that are no longer in use,
+independent of whether or not the ``tx_rs_thresh`` has been crossed.
+There are two scenarios when an application may want the mbuf released immediately:
+
+* When a given packet needs to be sent to multiple destination interfaces
+ (either for Layer 2 flooding or Layer 3 multi-cast).
+ One option is to make a copy of the packet or a copy of the header portion that needs to be manipulated.
+ A second option is to transmit the packet and then poll the ``rte_eth_tx_done_cleanup()`` API
+ until the reference count on the packet is decremented.
+ Then the same packet can be transmitted to the next destination interface.
+ The application is still responsible for managing any packet manipulations needed
+ between the different destination interfaces, but a packet copy can be avoided.
+ This API is independent of whether the packet was transmitted or dropped,
+ only that the mbuf is no longer in use by the interface.
+
+* Some applications are designed to make multiple runs, like a packet generator.
+ For performance reasons and consistency between runs,
+ the application may want to reset back to an initial state
+ between each run, where all mbufs are returned to the mempool.
+ In this case, it can call the ``rte_eth_tx_done_cleanup()`` API
+ for each destination interface it has been using
+ to request it to release of all its used mbufs.
+
+To determine if a driver supports this API, check for the *Free Tx mbuf on demand* feature
+in the *Network Interface Controller Drivers* document.
+
Hardware Offload
~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~
The Ethernet device API exported by the Ethernet PMDs is described in the *DPDK API Reference*.
+
+Extended Statistics API
+~~~~~~~~~~~~~~~~~~~~~~~
+
+The extended statistics API allows each individual PMD to expose a unique set
+of statistics. Accessing these from application programs is done via two
+functions:
+
+* ``rte_eth_xstats_get``: Fills in an array of ``struct rte_eth_xstat``
+ with extended statistics.
+* ``rte_eth_xstats_get_names``: Fills in an array of
+ ``struct rte_eth_xstat_name`` with extended statistic name lookup
+ information.
+
+Each ``struct rte_eth_xstat`` contains an identifier and value pair, and
+each ``struct rte_eth_xstat_name`` contains a string. Each identifier
+within the ``struct rte_eth_xstat`` lookup array must have a corresponding
+entry in the ``struct rte_eth_xstat_name`` lookup array. Within the latter
+the index of the entry is the identifier the string is associated with.
+These identifiers, as well as the number of extended statistic exposed, must
+remain constant during runtime. Note that extended statistic identifiers are
+driver-specific, and hence might not be the same for different ports.
+
+A naming scheme exists for the strings exposed to clients of the API. This is
+to allow scraping of the API for statistics of interest. The naming scheme uses
+strings split by a single underscore ``_``. The scheme is as follows:
+
+* direction
+* detail 1
+* detail 2
+* detail n
+* unit
+
+Examples of common statistics xstats strings, formatted to comply to the scheme
+proposed above:
+
+* ``rx_bytes``
+* ``rx_crc_errors``
+* ``tx_multicast_packets``
+
+The scheme, although quite simple, allows flexibility in presenting and reading
+information from the statistic strings. The following example illustrates the
+naming scheme:``rx_packets``. In this example, the string is split into two
+components. The first component ``rx`` indicates that the statistic is
+associated with the receive side of the NIC. The second component ``packets``
+indicates that the unit of measure is packets.
+
+A more complicated example: ``tx_size_128_to_255_packets``. In this example,
+``tx`` indicates transmission, ``size`` is the first detail, ``128`` etc are
+more details, and ``packets`` indicates that this is a packet counter.
+
+Some additions in the metadata scheme are as follows:
+
+* If the first part does not match ``rx`` or ``tx``, the statistic does not
+ have an affinity with either receive of transmit.
+
+* If the first letter of the second part is ``q`` and this ``q`` is followed
+ by a number, this statistic is part of a specific queue.
+
+An example where queue numbers are used is as follows: ``tx_q7_bytes`` which
+indicates this statistic applies to queue number 7, and represents the number
+of transmitted bytes on that queue.
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