doc: add Rx and Tx callbacks sample app user guide
Added a sample application guide for the rxtx_callbacks app. Signed-off-by: John McNamara <john.mcnamara@intel.com> Acked-by: Siobhan Butler <siobhan.a.butler@intel.com> Acked-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
This commit is contained in:
John McNamara
Thomas Monjalon
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@ -463,6 +463,7 @@ F: doc/guides/sample_app_ug/quota_watermark.rst
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M: Bruce Richardson <bruce.richardson@intel.com>
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M: John McNamara <john.mcnamara@intel.com>
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F: examples/rxtx_callbacks/
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F: doc/guides/sample_app_ug/rxtx_callbacks.rst
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M: Bruce Richardson <bruce.richardson@intel.com>
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M: John McNamara <john.mcnamara@intel.com>
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@ -44,6 +44,7 @@ Sample Applications User Guide
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exception_path
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hello_world
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skeleton
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rxtx_callbacks
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ip_frag
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ipv4_multicast
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ip_reassembly
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251
doc/guides/sample_app_ug/rxtx_callbacks.rst
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251
doc/guides/sample_app_ug/rxtx_callbacks.rst
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@ -0,0 +1,251 @@
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.. BSD LICENSE
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Copyright(c) 2015 Intel Corporation. All rights reserved.
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All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions
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are met:
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* Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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* Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in
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the documentation and/or other materials provided with the
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distribution.
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* Neither the name of Intel Corporation nor the names of its
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contributors may be used to endorse or promote products derived
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from this software without specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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RX/TX Callbacks Sample Application
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==================================
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The RX/TX Callbacks sample application is a packet forwarding application that
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demonstrates the use of user defined callbacks on received and transmitted
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packets. The application performs a simple latency check, using callbacks, to
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determine the time packets spend within the application.
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In the sample application a user defined callback is applied to all received
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packets to add a timestamp. A separate callback is applied to all packets
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prior to transmission to calculate the elapsed time, in CPU cycles.
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Compiling the Application
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-------------------------
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To compile the application export the path to the DPDK source tree and go to
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the example directory:
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.. code-block:: console
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export RTE_SDK=/path/to/rte_sdk
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cd ${RTE_SDK}/examples/rxtx_callbacks
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Set the target, for example:
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.. code-block:: console
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export RTE_TARGET=x86_64-native-linuxapp-gcc
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See the *DPDK Getting Started* Guide for possible ``RTE_TARGET`` values.
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The callbacks feature requires that the ``CONFIG_RTE_ETHDEV_RXTX_CALLBACKS``
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setting is on in the ``config/common_`` config file that applies to the
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target. This is generally on by default:
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.. code-block:: console
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CONFIG_RTE_ETHDEV_RXTX_CALLBACKS=y
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Build the application as follows:
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.. code-block:: console
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make
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Running the Application
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-----------------------
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To run the example in a ``linuxapp`` environment:
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.. code-block:: console
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./build/rxtx_callbacks -c 2 -n 4
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Refer to *DPDK Getting Started Guide* for general information on running
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applications and the Environment Abstraction Layer (EAL) options.
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Explanation
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-----------
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The ``rxtx_callbacks`` application is mainly a simple forwarding application
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based on the :doc:`skeleton`. See that section of the documentation for more
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details of the forwarding part of the application.
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The sections below explain the additional RX/TX callback code.
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The Main Function
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~~~~~~~~~~~~~~~~~
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The ``main()`` function performs the application initialization and calls the
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execution threads for each lcore. This function is effectively identical to
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the ``main()`` function explained in :doc:`skeleton`.
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The ``lcore_main()`` function is also identical.
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The main difference is in the user defined ``port_init()`` function where the
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callbacks are added. This is explained in the next section:
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The Port Initialization Function
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The main functional part of the port initialization is shown below with
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comments:
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.. code-block:: c
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static inline int
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port_init(uint8_t port, struct rte_mempool *mbuf_pool)
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{
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struct rte_eth_conf port_conf = port_conf_default;
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const uint16_t rx_rings = 1, tx_rings = 1;
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struct ether_addr addr;
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int retval;
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uint16_t q;
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if (port >= rte_eth_dev_count())
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return -1;
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/* Configure the Ethernet device. */
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retval = rte_eth_dev_configure(port, rx_rings, tx_rings, &port_conf);
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if (retval != 0)
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return retval;
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/* Allocate and set up 1 RX queue per Ethernet port. */
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for (q = 0; q < rx_rings; q++) {
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retval = rte_eth_rx_queue_setup(port, q, RX_RING_SIZE,
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rte_eth_dev_socket_id(port), NULL, mbuf_pool);
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if (retval < 0)
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return retval;
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}
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/* Allocate and set up 1 TX queue per Ethernet port. */
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for (q = 0; q < tx_rings; q++) {
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retval = rte_eth_tx_queue_setup(port, q, TX_RING_SIZE,
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rte_eth_dev_socket_id(port), NULL);
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if (retval < 0)
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return retval;
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}
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/* Start the Ethernet port. */
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retval = rte_eth_dev_start(port);
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if (retval < 0)
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return retval;
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/* Enable RX in promiscuous mode for the Ethernet device. */
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rte_eth_promiscuous_enable(port);
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/* Add the callbacks for RX and TX.*/
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rte_eth_add_rx_callback(port, 0, add_timestamps, NULL);
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rte_eth_add_tx_callback(port, 0, calc_latency, NULL);
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return 0;
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}
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The RX and TX callbacks are added to the ports/queues as function pointers:
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.. code-block:: c
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rte_eth_add_rx_callback(port, 0, add_timestamps, NULL);
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rte_eth_add_tx_callback(port, 0, calc_latency, NULL);
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More than one callback can be added and additional information can be passed
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to callback function pointers as a ``void*``. In the examples above ``NULL``
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is used.
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The ``add_timestamps()`` and ``calc_latency()`` functions are explained below.
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The add_timestamps() Callback
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The ``add_timestamps()`` callback is added to the RX port and is applied to
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all packets received:
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.. code-block:: c
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static uint16_t
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add_timestamps(uint8_t port __rte_unused, uint16_t qidx __rte_unused,
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struct rte_mbuf **pkts, uint16_t nb_pkts, void *_ __rte_unused)
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{
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unsigned i;
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uint64_t now = rte_rdtsc();
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for (i = 0; i < nb_pkts; i++)
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pkts[i]->udata64 = now;
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return nb_pkts;
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}
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The DPDK function ``rte_rdtsc()`` is used to add a cycle count timestamp to
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each packet (see the *cycles* section of the *DPDK API Documentation* for
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details).
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The calc_latency() Callback
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~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The ``calc_latency()`` callback is added to the TX port and is applied to all
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packets prior to transmission:
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.. code-block:: c
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static uint16_t
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calc_latency(uint8_t port __rte_unused, uint16_t qidx __rte_unused,
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struct rte_mbuf **pkts, uint16_t nb_pkts, void *_ __rte_unused)
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{
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uint64_t cycles = 0;
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uint64_t now = rte_rdtsc();
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unsigned i;
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for (i = 0; i < nb_pkts; i++)
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cycles += now - pkts[i]->udata64;
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latency_numbers.total_cycles += cycles;
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latency_numbers.total_pkts += nb_pkts;
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if (latency_numbers.total_pkts > (100 * 1000 * 1000ULL)) {
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printf("Latency = %"PRIu64" cycles\n",
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latency_numbers.total_cycles / latency_numbers.total_pkts);
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latency_numbers.total_cycles = latency_numbers.total_pkts = 0;
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}
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return nb_pkts;
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}
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The ``calc_latency()`` function accumulates the total number of packets and
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the total number of cycles used. Once more than 100 million packets have been
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transmitted the average cycle count per packet is printed out and the counters
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are reset.
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