xref: /dpdk/doc/guides/sample_app_ug/hello_world.rst (revision daa02b5cddbb8e11b31d41e2bf7bb1ae64dcae2f)
1..  SPDX-License-Identifier: BSD-3-Clause
2    Copyright(c) 2010-2014 Intel Corporation.
3
4Hello World Sample Application
5==============================
6
7The Hello World sample application is an example of the simplest DPDK application that can be written.
8The application simply prints an "helloworld" message on every enabled lcore.
9
10Compiling the Application
11-------------------------
12
13To compile the sample application see :doc:`compiling`.
14
15The application is located in the ``helloworld`` sub-directory.
16
17Running the Application
18-----------------------
19
20To run the example in a linux environment:
21
22.. code-block:: console
23
24    $ ./<build_dir>/examples/dpdk-helloworld -l 0-3 -n 4
25
26Refer to *DPDK Getting Started Guide* for general information on running applications
27and the Environment Abstraction Layer (EAL) options.
28
29Explanation
30-----------
31
32The following sections provide some explanation of code.
33
34EAL Initialization
35~~~~~~~~~~~~~~~~~~
36
37The first task is to initialize the Environment Abstraction Layer (EAL).
38This is done in the main() function using the following code:
39
40.. literalinclude:: ../../../examples/helloworld/main.c
41    :language: c
42    :start-after: Initialization of Environment Abstraction Layer (EAL). 8<
43    :end-before: >8 End of initialization of Environment Abstraction Layer
44
45This call finishes the initialization process that was started before main() is called (in case of a Linux environment).
46The argc and argv arguments are provided to the rte_eal_init() function.
47The value returned is the number of parsed arguments.
48
49Starting Application Unit Lcores
50~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
51
52Once the EAL is initialized, the application is ready to launch a function on an lcore.
53In this example, lcore_hello() is called on every available lcore.
54The following is the definition of the function:
55
56.. literalinclude:: ../../../examples/helloworld/main.c
57    :language: c
58    :start-after: Launch a function on lcore. 8<
59    :end-before: >8 End of launching function on lcore.
60
61The code that launches the function on each lcore is as follows:
62
63.. literalinclude:: ../../../examples/helloworld/main.c
64    :language: c
65    :start-after: Launches the function on each lcore. 8<
66    :end-before: >8 End of launching the function on each lcore.
67    :dedent: 1
68
69The following code is equivalent and simpler:
70
71.. literalinclude:: ../../../examples/helloworld/main.c
72    :language: c
73    :start-after: Simpler equivalent. 8<
74    :end-before: >8 End of simpler equivalent.
75    :dedent: 2
76
77Refer to the *DPDK API Reference* for detailed information on the rte_eal_mp_remote_launch() function.
78