xref: /dpdk/doc/guides/sample_app_ug/l2_forward_event.rst (revision 8750576fb2a9a067ffbcce4bab6481f3bfa47097)

..  SPDX-License-Identifier: BSD-3-Clause
    Copyright(c) 2010-2014 Intel Corporation.

L2 Forwarding Eventdev Sample Application
=========================================

The L2 Forwarding eventdev sample application is an example of
packet processing using the Data Plane Development Kit (DPDK)
to demonstrate the usage of the poll and event mode packet I/O mechanism.

Overview
--------

The L2 forwarding eventdev sample application performs
L2 forwarding for each packet that is received on an Rx port.
The destination port is the adjacent port from the enabled portmask.
If the first four ports are enabled (portmask=0x0f),
ports 1 and 2 forward into each other,
and ports 3 and 4 forward into each other.
Also, if MAC address updating is enabled,
the MAC addresses are affected as follows:

*   The source MAC address is replaced by the Tx port MAC address
*   The destination MAC address is replaced by 02:00:00:00:00:<Tx port>

Application receives packets from Rx port using these methods:

*   Poll mode
*   Eventdev mode (default)

This application can be used to benchmark performance using a traffic-generator,
as shown in the :numref:`figure_l2fwd_event_benchmark_setup`.

.. _figure_l2fwd_event_benchmark_setup:

.. figure:: img/l2_fwd_benchmark_setup.*

   Performance Benchmark Setup (Basic Environment)

Compiling the Application
-------------------------

To compile the sample application, see :doc:`compiling`.

The application is located in the ``l2fwd-event`` sub-directory.

Running the Application
-----------------------

The application requires a number of command line options:

.. code-block:: console

    ./<build_dir>/examples/dpdk-l2fwd-event [EAL options] -- -p PORTMASK
                                                        [-q NQ]
                                                        [--[no-]mac-updating]
                                                        [--mode=MODE]
                                                        [--eventq-sched=SCHED_MODE]
                                                        [--event-vector [--event-vector-size SIZE] [--event-vector-tmo NS]]

where,

*   p PORTMASK: A hexadecimal bitmask of the ports to configure

*   q NQ: Maximum number of queues per lcore (default is 1)

*   --[no-]mac-updating: Enable or disable MAC addresses updating (enabled by default).

*   --mode=MODE: Packet transfer mode for I/O, poll or eventdev. Eventdev by default.

*   --eventq-sched=SCHED_MODE: Event queue schedule mode, Ordered, Atomic or Parallel. Atomic by default.

*   --config: Configure forwarding port pair mapping. Alternate port pairs by default.

*   --event-vector: Enable event vectorization. Only valid if --mode=eventdev.

*   --event-vector-size: Max vector size if event vectorization is enabled.

*   --event-vector-tmo: Max timeout to form vector in nanoseconds if event vectorization is enabled.

Sample usage commands are given below to run the application into different modes:

Poll mode with 4 lcores, 16 ports and 8 RX queues per lcore and MAC address updating enabled,
issue the command:

.. code-block:: console

    ./<build_dir>/examples/dpdk-l2fwd-event -l 0-3 -n 4 -- -q 8 -p ffff --mode=poll

Eventdev mode with 4 lcores, 16 ports, schedule method ordered and MAC address updating enabled,
issue the command:

.. code-block:: console

    ./<build_dir>/examples/dpdk-l2fwd-event -l 0-3 -n 4 -- -p ffff --eventq-sched=ordered

or

.. code-block:: console

    ./<build_dir>/examples/dpdk-l2fwd-event -l 0-3 -n 4 -- -q 8 -p ffff --mode=eventdev --eventq-sched=ordered

Refer to the *DPDK Getting Started Guide* for general information on running
applications and Environment Abstraction Layer (EAL) options.

To run the application with S/W scheduler, it uses following DPDK services:

*   Software scheduler
*   Rx adapter service function
*   Tx adapter service function

The application needs service cores to run the above mentioned services.
Service cores must be provided as EAL parameters
along with the ``--vdev=event_sw0`` to enable S/W scheduler.
The following is the sample command:

.. code-block:: console

    ./<build_dir>/examples/dpdk-l2fwd-event -l 0-7 -s 0-3 -n 4 --vdev event_sw0 -- -q 8 -p ffff --mode=eventdev --eventq-sched=ordered

Explanation
-----------

The following sections provide an explanation of the code.

.. _l2_fwd_event_app_cmd_arguments:

Command Line Arguments
~~~~~~~~~~~~~~~~~~~~~~

The L2 forwarding eventdev sample application takes specific parameters
and Environment Abstraction Layer (EAL) arguments.
The preferred way to parse parameters is to use the ``getopt()`` function
since it is part of a well-defined and portable library.

The parsing of arguments is done in the ``l2fwd_parse_args()`` function
for non-eventdev parameters
and in ``parse_eventdev_args()`` for eventdev parameters.
This method of argument parsing is not described here.
Refer to the *glibc getopt(3)* main page for details.

EAL arguments are parsed first, then application-specific arguments follow.
This is done at the beginning of the ``main()`` function and eventdev parameters
are parsed in ``eventdev_resource_setup()`` function during eventdev setup:

.. literalinclude:: ../../../examples/l2fwd-event/main.c
        :language: c
        :start-after: Init EAL. 8<
        :end-before: >8 End of init EAL.
        :dedent: 1

Mbuf Pool Initialization
~~~~~~~~~~~~~~~~~~~~~~~~

Once the arguments are parsed, the mbuf pool is created.
The mbuf pool contains a set of mbuf objects that will be used by the driver
and the application to store network packet data:

.. literalinclude:: ../../../examples/l2fwd-event/main.c
        :language: c
        :start-after: Create the mbuf pool. 8<
        :end-before: >8 End of creation of mbuf pool.
        :dedent: 1

The rte_mempool is a generic structure used to handle pools of objects.
In this case, it is necessary to create a pool that will be used by the driver.
The number of allocated mbufs is ``NB_MBUF``,
with a data room size of ``RTE_MBUF_DEFAULT_BUF_SIZE`` each.
A per-lcore cache of 32 mbufs is kept.
The memory is allocated in NUMA socket 0,
but it is possible to extend this code to allocate one mbuf pool per socket.

The ``rte_pktmbuf_pool_create()`` function uses the default mbuf pool
and mbuf initializers, respectively ``rte_pktmbuf_pool_init()`` and ``rte_pktmbuf_init()``.
An advanced application may want to use the mempool API to create the
mbuf pool with more control.

.. _l2_fwd_event_app_drv_init:

Driver Initialization
~~~~~~~~~~~~~~~~~~~~~

The main part of the code in the ``main()`` function relates to the initialization
of the driver. To fully understand this code, it is recommended to study the
chapters related to the Poll Mode and Event mode Driver in the
*DPDK Programmer's Guide* - Rel 1.4 EAR and the *DPDK API Reference*.

.. literalinclude:: ../../../examples/l2fwd-event/main.c
        :language: c
        :start-after: Reset l2fwd_dst_ports. 8<
        :end-before: >8 End of reset l2fwd_dst_ports.
        :dedent: 1

The next step is to configure the RX and TX queues. For each port, there is only
one RX queue (only one lcore is able to poll a given port). The number of TX
queues depends on the number of available lcores. The ``rte_eth_dev_configure()``
function is used to configure the number of queues for a port:

.. literalinclude:: ../../../examples/l2fwd-event/l2fwd_common.c
        :language: c
        :start-after: Configure RX and TX queue. 8<
        :end-before: >8 End of configuration RX and TX queue.
        :dedent: 2

RX Queue Initialization
~~~~~~~~~~~~~~~~~~~~~~~

The application uses one lcore to poll one or several ports, depending on the -q
option, which specifies the number of queues per lcore.

For example, if the user specifies -q 4, the application is able to poll four
ports with one lcore. If there are 16 ports on the target (and if the portmask
argument is -p ffff ), the application will need four lcores to poll all the
ports.

.. literalinclude:: ../../../examples/l2fwd-event/l2fwd_common.c
        :language: c
        :start-after: Using lcore to poll one or several ports. 8<
        :end-before: >8 End of using lcore to poll one or several ports.
        :dedent: 2

The list of queues that must be polled for a given lcore is stored in a private
structure called struct lcore_queue_conf.

.. literalinclude:: ../../../examples/l2fwd/main.c
        :language: c
        :start-after: List of queues to be polled for a given lcore. 8<
        :end-before: >8 End of list of queues to be polled for a given lcore.

The values n_rx_port and rx_port_list[] are used in the main packet processing
loop (see :ref:`l2_fwd_event_app_rx_tx_packets`).

.. _l2_fwd_event_app_tx_init:

TX Queue Initialization
~~~~~~~~~~~~~~~~~~~~~~~

Each lcore should be able to transmit on any port. For each port, a single TX
queue is initialized.

.. literalinclude:: ../../../examples/l2fwd-event/l2fwd_common.c
        :language: c
        :start-after: Init one TX queue on each port. 8<
        :end-before: >8 End of init one TX queue on each port.
        :dedent: 2

To configure eventdev support, the application sets up following components:

*   Event dev
*   Event queue
*   Event Port
*   Rx/Tx adapters
*   Ethernet ports

.. _l2_fwd_event_app_event_dev_init:

Event device Initialization
~~~~~~~~~~~~~~~~~~~~~~~~~~~

Application can use either H/W or S/W based event device scheduler
implementation and supports single instance of event device. It configures event
device as per the following configuration:

.. literalinclude:: ../../../examples/l2fwd-event/l2fwd_event_generic.c
        :language: c
        :start-after: Configures event device as per below configuration. 8<
        :end-before: >8 End of configuration event device as per below configuration.
        :dedent: 1

In case of S/W scheduler, the application runs eventdev
scheduler service on the service core.
The application retrieves the service id
and finds the best possible service core to run S/W scheduler.

.. literalinclude:: ../../../examples/l2fwd-event/l2fwd_event.c
        :language: c
        :start-after: Running eventdev scheduler service on service core. 8<
        :end-before: >8 End of running eventdev scheduler service on service core.
        :dedent: 1

Event queue Initialization
~~~~~~~~~~~~~~~~~~~~~~~~~~

Each Ethernet device is assigned a dedicated event queue which will be linked
to all available event ports, i.e. each lcore can dequeue packets from any of the
Ethernet ports.

.. literalinclude:: ../../../examples/l2fwd-event/l2fwd_event_generic.c
        :language: c
        :start-after: Event queue initialization. 8<
        :end-before: >8 End of event queue initialization.
        :dedent: 1

In case of S/W scheduler, an extra event queue is created which will be used for
Tx adapter service function for enqueue operation.

.. _l2_fwd_app_event_port_init:

Event port Initialization
~~~~~~~~~~~~~~~~~~~~~~~~~

Each worker thread is assigned a dedicated event port for enq/deq operations
to/from an event device.
All event ports are linked to all available event queues.

.. literalinclude:: ../../../examples/l2fwd-event/l2fwd_event_generic.c
        :language: c
        :start-after: Event port initialization. 8<
        :end-before: >8 End of event port initialization.
        :dedent: 1

In case of S/W scheduler, an extra event port is created by the DPDK library
which is retrieved by the application.
It will be used by Tx adapter service.

.. literalinclude:: ../../../examples/l2fwd-event/l2fwd_event_generic.c
        :language: c
        :start-after: Extra port created. 8<
        :end-before: >8 End of extra port created.
        :dedent: 1

Rx/Tx adapter Initialization
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Each Ethernet port is assigned a dedicated Rx/Tx adapter for H/W scheduler. Each
Ethernet port's Rx queues are connected to its respective event queue at
priority 0 via Rx adapter configuration and Ethernet port's tx queues are
connected via Tx adapter.

.. literalinclude:: ../../../examples/l2fwd-event/l2fwd_event_internal_port.c
        :language: c
        :start-after: Assigned ethernet port. 8<
        :end-before: >8 End of assigned ethernet port.
        :dedent: 1

For S/W scheduler instead of dedicated adapters, common Rx/Tx adapters are
configured which will be shared among all the Ethernet ports.
Also, the DPDK library needs service cores to run internal services for Rx/Tx adapters.
The application gets a service id for Rx/Tx adapters.
After a successful setup, it runs the services on dedicated service cores.

.. literalinclude:: ../../../examples/l2fwd-event/l2fwd_event.c
        :language: c
        :start-after: Gets service ID for RX/TX adapters. 8<
        :end-before: >8 End of get service ID for RX/TX adapters.
        :dedent: 1

.. _l2_fwd_event_app_rx_tx_packets:

Receive, Process and Transmit Packets
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In the ``l2fwd_main_loop()`` function,
the main task is to read ingress packets from the Rx queues.
This is done using the following code:

.. literalinclude:: ../../../examples/l2fwd-event/l2fwd_poll.c
        :language: c
        :start-after: Reading ingress packets. 8<
        :end-before: >8 End of reading ingress packets.
        :dedent: 2

Packets are read in a burst of size ``MAX_PKT_BURST``.
The ``rte_eth_rx_burst()`` function writes the mbuf pointers
in a local table and returns the number of available mbufs in the table.

Then, each mbuf in the table is processed by the ``l2fwd_simple_forward()`` function.
The processing is very simple: process the Tx port from the Rx port,
then replace the source and destination MAC addresses if MAC address updating is enabled.

During the initialization process, a static array of destination ports
(``l2fwd_dst_ports[]``) is filled so that for each source port, a destination port
is assigned that is either the next or previous enabled port from the portmask.
If the number of ports are odd in portmask, then the packet from the last port will be
forwarded to first port i.e. if portmask=0x07, then forwarding will take place
like p0--->p1, p1--->p2, p2--->p0.

Also, to optimize enqueue operation, ``l2fwd_simple_forward()`` stores incoming mbufs
up to ``MAX_PKT_BURST``.
Once it reaches the limit, all packets are transmitted to destination ports.

.. literalinclude:: ../../../examples/l2fwd/main.c
        :language: c
        :start-after: Simple forward. 8<
        :end-before: >8 End of simple forward.

For this test application, the processing is exactly the same for all packets
arriving on the same RX port. Therefore, it would have been possible to call
the ``rte_eth_tx_buffer()`` function directly from the main loop to send all the
received packets on the same TX port, using the burst-oriented send function,
which is more efficient.

However, in real-life applications (such as L3 routing),
packet N is not necessarily forwarded on the same port as packet N-1.
The application is implemented to illustrate so the same approach can be
reused in a more complex application.

To ensure that no packets remain in the tables, each lcore does a draining of TX
queue in its main loop. This technique introduces some latency when there are
not many packets to send. However, it improves performance:

.. literalinclude:: ../../../examples/l2fwd-event/l2fwd_poll.c
        :language: c
        :start-after: Draining TX queue in main loop. 8<
        :end-before: >8 End of draining TX queue in main loop.
        :dedent: 2

In the ``l2fwd_event_loop()`` function,
the main task is to read ingress packets from the event ports.
This is done using the following code:

.. literalinclude:: ../../../examples/l2fwd-event/l2fwd_event.c
        :language: c
        :start-after: Read packet from eventdev. 8<
        :end-before: >8 End of reading packets from eventdev.
        :dedent: 2

Before reading packets, ``deq_len`` is fetched
to ensure the correct allowed deq length by the eventdev.
The ``rte_event_dequeue_burst()`` function writes the mbuf pointers in a local table
and returns the number of available mbufs in the table.

Then, each mbuf in the table is processed by the ``l2fwd_eventdev_forward()``
function. The processing is very simple: process the TX port from the RX port,
then replace the source and destination MAC addresses if MAC address updating
is enabled.

During the initialization process, a static array of destination ports
(``l2fwd_dst_ports[]``) is filled so that for each source port, a destination port
is assigned that is either the next or previous enabled port from the portmask.
If number of ports are odd in portmask then packet from last port will be
forwarded to first port i.e. if portmask=0x07, then forwarding will take place
like p0--->p1, p1--->p2, p2--->p0.

``l2fwd_eventdev_forward()`` does not stores incoming mbufs.
The packet will forwarded to destination ports
via Tx adapter or generic event dev enqueue API
depending H/W or S/W scheduler is used.

.. literalinclude:: ../../../examples/l2fwd-event/l2fwd_event.c
        :language: c
        :start-after: Read packet from eventdev. 8<
        :end-before: >8 End of reading packets from eventdev.
        :dedent: 2