--- /dev/null
+.. BSD LICENSE
+ Copyright(c) 2015 Intel Corporation. All rights reserved.
+ All rights reserved.
+
+ Redistribution and use in source and binary forms, with or without
+ modification, are permitted provided that the following conditions
+ are met:
+
+ * Redistributions of source code must retain the above copyright
+ notice, this list of conditions and the following disclaimer.
+ * Redistributions in binary form must reproduce the above copyright
+ notice, this list of conditions and the following disclaimer in
+ the documentation and/or other materials provided with the
+ distribution.
+ * Neither the name of Intel Corporation nor the names of its
+ contributors may be used to endorse or promote products derived
+ from this software without specific prior written permission.
+
+ THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+
+RX/TX Callbacks Sample Application
+==================================
+
+The RX/TX Callbacks sample application is a packet forwarding application that
+demonstrates the use of user defined callbacks on received and transmitted
+packets. The application performs a simple latency check, using callbacks, to
+determine the time packets spend within the application.
+
+In the sample application a user defined callback is applied to all received
+packets to add a timestamp. A separate callback is applied to all packets
+prior to transmission to calculate the elapsed time, in CPU cycles.
+
+
+Compiling the Application
+-------------------------
+
+To compile the application export the path to the DPDK source tree and go to
+the example directory:
+
+.. code-block:: console
+
+ export RTE_SDK=/path/to/rte_sdk
+
+ cd ${RTE_SDK}/examples/rxtx_callbacks
+
+
+Set the target, for example:
+
+.. code-block:: console
+
+ export RTE_TARGET=x86_64-native-linuxapp-gcc
+
+See the *DPDK Getting Started* Guide for possible ``RTE_TARGET`` values.
+
+The callbacks feature requires that the ``CONFIG_RTE_ETHDEV_RXTX_CALLBACKS``
+setting is on in the ``config/common_`` config file that applies to the
+target. This is generally on by default:
+
+.. code-block:: console
+
+ CONFIG_RTE_ETHDEV_RXTX_CALLBACKS=y
+
+Build the application as follows:
+
+.. code-block:: console
+
+ make
+
+
+Running the Application
+-----------------------
+
+To run the example in a ``linuxapp`` environment:
+
+.. code-block:: console
+
+ ./build/rxtx_callbacks -c 2 -n 4
+
+Refer to *DPDK Getting Started Guide* for general information on running
+applications and the Environment Abstraction Layer (EAL) options.
+
+
+
+Explanation
+-----------
+
+The ``rxtx_callbacks`` application is mainly a simple forwarding application
+based on the :doc:`skeleton`. See that section of the documentation for more
+details of the forwarding part of the application.
+
+The sections below explain the additional RX/TX callback code.
+
+
+The Main Function
+~~~~~~~~~~~~~~~~~
+
+The ``main()`` function performs the application initialization and calls the
+execution threads for each lcore. This function is effectively identical to
+the ``main()`` function explained in :doc:`skeleton`.
+
+The ``lcore_main()`` function is also identical.
+
+The main difference is in the user defined ``port_init()`` function where the
+callbacks are added. This is explained in the next section:
+
+
+The Port Initialization Function
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The main functional part of the port initialization is shown below with
+comments:
+
+.. code-block:: c
+
+ static inline int
+ port_init(uint8_t port, struct rte_mempool *mbuf_pool)
+ {
+ struct rte_eth_conf port_conf = port_conf_default;
+ const uint16_t rx_rings = 1, tx_rings = 1;
+ struct ether_addr addr;
+ int retval;
+ uint16_t q;
+
+ if (port >= rte_eth_dev_count())
+ return -1;
+
+ /* Configure the Ethernet device. */
+ retval = rte_eth_dev_configure(port, rx_rings, tx_rings, &port_conf);
+ if (retval != 0)
+ return retval;
+
+ /* Allocate and set up 1 RX queue per Ethernet port. */
+ for (q = 0; q < rx_rings; q++) {
+ retval = rte_eth_rx_queue_setup(port, q, RX_RING_SIZE,
+ rte_eth_dev_socket_id(port), NULL, mbuf_pool);
+ if (retval < 0)
+ return retval;
+ }
+
+ /* Allocate and set up 1 TX queue per Ethernet port. */
+ for (q = 0; q < tx_rings; q++) {
+ retval = rte_eth_tx_queue_setup(port, q, TX_RING_SIZE,
+ rte_eth_dev_socket_id(port), NULL);
+ if (retval < 0)
+ return retval;
+ }
+
+ /* Start the Ethernet port. */
+ retval = rte_eth_dev_start(port);
+ if (retval < 0)
+ return retval;
+
+ /* Enable RX in promiscuous mode for the Ethernet device. */
+ rte_eth_promiscuous_enable(port);
+
+
+ /* Add the callbacks for RX and TX.*/
+ rte_eth_add_rx_callback(port, 0, add_timestamps, NULL);
+ rte_eth_add_tx_callback(port, 0, calc_latency, NULL);
+
+ return 0;
+ }
+
+
+The RX and TX callbacks are added to the ports/queues as function pointers:
+
+.. code-block:: c
+
+ rte_eth_add_rx_callback(port, 0, add_timestamps, NULL);
+ rte_eth_add_tx_callback(port, 0, calc_latency, NULL);
+
+More than one callback can be added and additional information can be passed
+to callback function pointers as a ``void*``. In the examples above ``NULL``
+is used.
+
+The ``add_timestamps()`` and ``calc_latency()`` functions are explained below.
+
+
+The add_timestamps() Callback
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The ``add_timestamps()`` callback is added to the RX port and is applied to
+all packets received:
+
+.. code-block:: c
+
+ static uint16_t
+ add_timestamps(uint8_t port __rte_unused, uint16_t qidx __rte_unused,
+ struct rte_mbuf **pkts, uint16_t nb_pkts, void *_ __rte_unused)
+ {
+ unsigned i;
+ uint64_t now = rte_rdtsc();
+
+ for (i = 0; i < nb_pkts; i++)
+ pkts[i]->udata64 = now;
+
+ return nb_pkts;
+ }
+
+The DPDK function ``rte_rdtsc()`` is used to add a cycle count timestamp to
+each packet (see the *cycles* section of the *DPDK API Documentation* for
+details).
+
+
+The calc_latency() Callback
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The ``calc_latency()`` callback is added to the TX port and is applied to all
+packets prior to transmission:
+
+.. code-block:: c
+
+ static uint16_t
+ calc_latency(uint8_t port __rte_unused, uint16_t qidx __rte_unused,
+ struct rte_mbuf **pkts, uint16_t nb_pkts, void *_ __rte_unused)
+ {
+ uint64_t cycles = 0;
+ uint64_t now = rte_rdtsc();
+ unsigned i;
+
+ for (i = 0; i < nb_pkts; i++)
+ cycles += now - pkts[i]->udata64;
+
+ latency_numbers.total_cycles += cycles;
+ latency_numbers.total_pkts += nb_pkts;
+
+ if (latency_numbers.total_pkts > (100 * 1000 * 1000ULL)) {
+ printf("Latency = %"PRIu64" cycles\n",
+ latency_numbers.total_cycles / latency_numbers.total_pkts);
+
+ latency_numbers.total_cycles = latency_numbers.total_pkts = 0;
+ }
+
+ return nb_pkts;
+ }
+
+The ``calc_latency()`` function accumulates the total number of packets and
+the total number of cycles used. Once more than 100 million packets have been
+transmitted the average cycle count per packet is printed out and the counters
+are reset.
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