packets to add a timestamp. A separate callback is applied to all packets
prior to transmission to calculate the elapsed time, in CPU cycles.
+If hardware timestamping is supported by the NIC, the sample application will
+also display the average latency since the packet was timestamped in hardware,
+on top of the latency since the packet was received and processed by the RX
+callback.
Compiling the Application
-------------------------
The application is located in the ``rxtx_callbacks`` sub-directory.
-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
Running the Application
-----------------------
.. code-block:: console
- ./build/rxtx_callbacks -l 1 -n 4
+ ./<build_dir>/examples/dpdk-rxtx_callbacks -l 1 -n 4 -- [-t]
+
+Use -t to enable hardware timestamping. If not supported by the NIC, an error
+will be displayed.
Refer to *DPDK Getting Started Guide* for general information on running
applications and the Environment Abstraction Layer (EAL) options.
The main functional part of the port initialization is shown below with
comments:
-.. code-block:: c
-
- static inline int
- port_init(uint16_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 rte_ether_addr addr;
- int retval;
- uint16_t q;
-
- /* 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;
- }
+.. literalinclude:: ../../../examples/rxtx_callbacks/main.c
+ :language: c
+ :start-after: Port initialization. 8<
+ :end-before: >8 End of port initialization.
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);
+.. literalinclude:: ../../../examples/rxtx_callbacks/main.c
+ :language: c
+ :start-after: RX and TX callbacks are added to the ports. 8<
+ :end-before: >8 End of RX and TX callbacks.
+ :dedent: 1
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``
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(uint16_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;
- }
+.. literalinclude:: ../../../examples/rxtx_callbacks/main.c
+ :language: c
+ :start-after: Callback added to the RX port and applied to packets. 8<
+ :end-before: >8 End of callback addition and application.
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
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(uint16_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;
- }
+.. literalinclude:: ../../../examples/rxtx_callbacks/main.c
+ :language: c
+ :start-after: Callback is added to the TX port. 8<
+ :end-before: >8 End of callback addition.
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
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