9a212dc06c
Currently the sample app user guides use hard coded code snippets,
this patch changes these to use literalinclude which will dynamically
update the snippets as changes are made to the code.
This was introduced in commit 413c75c33c ("doc: show how to include
code in guides"). Comments within the sample apps were updated to
accommodate this as part of this patch. This will help to ensure that
the code within the sample app user guides is up to date and not out
of sync with the actual code.
Signed-off-by: Conor Fogarty <conor.fogarty@intel.com>
Signed-off-by: Conor Walsh <conor.walsh@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>
127 lines
4.1 KiB
ReStructuredText
127 lines
4.1 KiB
ReStructuredText
.. SPDX-License-Identifier: BSD-3-Clause
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Copyright(c) 2015 Intel Corporation.
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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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If hardware timestamping is supported by the NIC, the sample application will
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also display the average latency since the packet was timestamped in hardware,
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on top of the latency since the packet was received and processed by the RX
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callback.
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Compiling the Application
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-------------------------
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To compile the sample application see :doc:`compiling`.
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The application is located in the ``rxtx_callbacks`` sub-directory.
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Running the Application
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-----------------------
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To run the example in a ``linux`` environment:
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.. code-block:: console
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./<build_dir>/examples/dpdk-rxtx_callbacks -l 1 -n 4 -- [-t]
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Use -t to enable hardware timestamping. If not supported by the NIC, an error
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will be displayed.
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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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.. literalinclude:: ../../../examples/rxtx_callbacks/main.c
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:language: c
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:start-after: Port initialization. 8<
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:end-before: >8 End of port initialization.
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The RX and TX callbacks are added to the ports/queues as function pointers:
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.. literalinclude:: ../../../examples/rxtx_callbacks/main.c
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:language: c
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:start-after: RX and TX callbacks are added to the ports. 8<
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:end-before: >8 End of RX and TX callbacks.
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:dedent: 1
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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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.. literalinclude:: ../../../examples/rxtx_callbacks/main.c
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:language: c
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:start-after: Callback added to the RX port and applied to packets. 8<
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:end-before: >8 End of callback addition and application.
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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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.. literalinclude:: ../../../examples/rxtx_callbacks/main.c
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:language: c
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:start-after: Callback is added to the TX port. 8<
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:end-before: >8 End of callback addition.
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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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