diff mbox

[dpdk-dev,v2] doc: add l2fwd-jobstats user guide

Message ID 1426674039-13016-1-git-send-email-pawelx.wodkowski@intel.com (mailing list archive)
State Accepted, archived
Headers show

Commit Message

Wodkowski, PawelX March 18, 2015, 10:20 a.m. UTC
Signed-off-by: Pawel Wodkowski <pawelx.wodkowski@intel.com>
---

 Changes v2
  1. Fix trailing spaces and typos.
  2. Add maintaners claim

 MAINTAINERS                                       |   1 +
 doc/guides/sample_app_ug/index.rst                |   1 +
 doc/guides/sample_app_ug/l2_forward_job_stats.rst | 637 ++++++++++++++++++++++
 3 files changed, 639 insertions(+)
 create mode 100644 doc/guides/sample_app_ug/l2_forward_job_stats.rst

Comments

De Lara Guarch, Pablo March 27, 2015, 3:33 p.m. UTC | #1
> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Pawel Wodkowski
> Sent: Wednesday, March 18, 2015 10:21 AM
> To: dev@dpdk.org
> Subject: [dpdk-dev] [PATCH v2] doc: add l2fwd-jobstats user guide
> 
> Signed-off-by: Pawel Wodkowski <pawelx.wodkowski@intel.com>
> ---
> 
>  Changes v2
>   1. Fix trailing spaces and typos.
>   2. Add maintaners claim
> 

[...]

> diff --git a/doc/guides/sample_app_ug/l2_forward_job_stats.rst
> b/doc/guides/sample_app_ug/l2_forward_job_stats.rst
> new file mode 100644
> index 0000000..e25d7b1

[...]

> +        /* Pass target to indicate that this job is happy of time interval
> +         * in which it was called. */
> +        rte_jobstats_finish(&qconf->flush_job, qconf->flush_job.target);
> +    }
> +
> +.. |l2_fwd_benchmark_setup| image:: img/l2_fwd_benchmark_setup.svg
> +
> +.. |l2_fwd_virtenv_benchmark_setup| image::
> img/l2_fwd_virtenv_benchmark_setup.png
> --
> 1.9.1

PDF will not build due to the extension of the images. Can you change them from ".svg" to ".*"?

Thanks,
Pablo
Thomas Monjalon March 31, 2015, 12:19 a.m. UTC | #2
2015-03-27 15:33, De Lara Guarch, Pablo:
> > Signed-off-by: Pawel Wodkowski <pawelx.wodkowski@intel.com>
> > ---
> > 
> >  Changes v2
> >   1. Fix trailing spaces and typos.
> >   2. Add maintaners claim
> 
> PDF will not build due to the extension of the images. Can you change them from ".svg" to ".*"?

Applied with above fix, thanks
diff mbox

Patch

diff --git a/MAINTAINERS b/MAINTAINERS
index 07fdf5e..a82e2f0 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -391,6 +391,7 @@  Job statistics
 M: Pawel Wodkowski <pawelx.wodkowski@intel.com>
 F: lib/librte_jobstats/
 F: examples/l2fwd-jobstats/
+F: doc/guides/sample_app_ug/l2_forward_job_stats.rst
 
 
 Test Applications
diff --git a/doc/guides/sample_app_ug/index.rst b/doc/guides/sample_app_ug/index.rst
index 5720181..c89a2f0 100644
--- a/doc/guides/sample_app_ug/index.rst
+++ b/doc/guides/sample_app_ug/index.rst
@@ -47,6 +47,7 @@  Sample Applications User Guide
     ipv4_multicast
     ip_reassembly
     kernel_nic_interface
+    l2_forward_job_stats
     l2_forward_real_virtual
     l3_forward
     l3_forward_power_man
diff --git a/doc/guides/sample_app_ug/l2_forward_job_stats.rst b/doc/guides/sample_app_ug/l2_forward_job_stats.rst
new file mode 100644
index 0000000..e25d7b1
--- /dev/null
+++ b/doc/guides/sample_app_ug/l2_forward_job_stats.rst
@@ -0,0 +1,637 @@ 
+..  BSD LICENSE
+    Copyright(c) 2010-2015 Intel Corporation. All rights reserved.
+    All rights reserved.
+
+    Redistribution and use in source and binary forms, with or without
+    modification, are permitted provided that the following conditions
+    are met:
+
+    * Redistributions of source code must retain the above copyright
+    notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above copyright
+    notice, this list of conditions and the following disclaimer in
+    the documentation and/or other materials provided with the
+    distribution.
+    * Neither the name of Intel Corporation nor the names of its
+    contributors may be used to endorse or promote products derived
+    from this software without specific prior written permission.
+
+    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+    A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+    OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+    SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+    LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+L2 Forwarding Sample Application (in Real and Virtualized Environments) with core load statistics.
+==================================================================================================
+
+The L2 Forwarding sample application is a simple example of packet processing using
+the Data Plane Development Kit (DPDK) which
+also takes advantage of Single Root I/O Virtualization (SR-IOV) features in a virtualized environment.
+
+.. note::
+
+    This application is a variation of L2 Forwarding sample application. It demonstrate possible
+    scheme of job stats library usage therefore some parts of this document is identical with original
+    L2 forwarding application.
+
+Overview
+--------
+
+The L2 Forwarding sample application, which can operate in real and virtualized environments,
+performs L2 forwarding for each packet that is received.
+The destination port is the adjacent port from the enabled portmask, that is,
+if the first four ports are enabled (portmask 0xf),
+ports 1 and 2 forward into each other, and ports 3 and 4 forward into each other.
+Also, 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_ID
+
+This application can be used to benchmark performance using a traffic-generator, as shown in the Figure 3.
+
+The application can also be used in a virtualized environment as shown in Figure 4.
+
+The L2 Forwarding application can also be used as a starting point for developing a new application based on the DPDK.
+
+.. _figure_3:
+
+**Figure 3. Performance Benchmark Setup (Basic Environment)**
+
+.. image4_png has been replaced
+
+|l2_fwd_benchmark_setup|
+
+.. _figure_4:
+
+**Figure 4. Performance Benchmark Setup (Virtualized Environment)**
+
+.. image5_png has been renamed
+
+|l2_fwd_virtenv_benchmark_setup|
+
+Virtual Function Setup Instructions
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This application can use the virtual function available in the system and
+therefore can be used in a virtual machine without passing through
+the whole Network Device into a guest machine in a virtualized scenario.
+The virtual functions can be enabled in the host machine or the hypervisor with the respective physical function driver.
+
+For example, in a Linux* host machine, it is possible to enable a virtual function using the following command:
+
+.. code-block:: console
+
+    modprobe ixgbe max_vfs=2,2
+
+This command enables two Virtual Functions on each of Physical Function of the NIC,
+with two physical ports in the PCI configuration space.
+It is important to note that enabled Virtual Function 0 and 2 would belong to Physical Function 0
+and Virtual Function 1 and 3 would belong to Physical Function 1,
+in this case enabling a total of four Virtual Functions.
+
+Compiling the Application
+-------------------------
+
+#.  Go to the example directory:
+
+    .. code-block:: console
+
+        export RTE_SDK=/path/to/rte_sdk cd ${RTE_SDK}/examples/l2fwd-jobstats
+
+#.  Set the target (a default target is used if not specified). For example:
+
+    .. code-block:: console
+
+        export RTE_TARGET=x86_64-native-linuxapp-gcc
+
+    *See the DPDK Getting Started Guide* for possible RTE_TARGET values.
+
+#.  Build the application:
+
+    .. code-block:: console
+
+        make
+
+Running the Application
+-----------------------
+
+The application requires a number of command line options:
+
+.. code-block:: console
+
+    ./build/l2fwd-jobstats [EAL options] -- -p PORTMASK [-q NQ] [-l]
+
+where,
+
+*   p PORTMASK: A hexadecimal bitmask of the ports to configure
+
+*   q NQ: A number of queues (=ports) per lcore (default is 1)
+
+*   l: Use locale thousands separator when formatting big numbers.
+
+To run the application in linuxapp environment with 4 lcores, 16 ports, 8 RX queues per lcore and
+thousands  separator printing, issue the command:
+
+.. code-block:: console
+
+    $ ./build/l2fwd-jobstats -c f -n 4 -- -q 8 -p ffff -l
+
+Refer to the *DPDK Getting Started Guide* for general information on running applications
+and the Environment Abstraction Layer (EAL) options.
+
+Explanation
+-----------
+
+The following sections provide some explanation of the code.
+
+Command Line Arguments
+~~~~~~~~~~~~~~~~~~~~~~
+
+The L2 Forwarding sample application takes specific parameters,
+in addition to Environment Abstraction Layer (EAL) arguments (see Section 9.3).
+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.
+The method of argument parsing is not described here.
+Refer to the *glibc getopt(3)* man page for details.
+
+EAL arguments are parsed first, then application-specific arguments.
+This is done at the beginning of the main() function:
+
+.. code-block:: c
+
+    /* init EAL */
+
+    ret = rte_eal_init(argc, argv);
+    if (ret < 0)
+        rte_exit(EXIT_FAILURE, "Invalid EAL arguments\n");
+
+    argc -= ret;
+    argv += ret;
+
+    /* parse application arguments (after the EAL ones) */
+
+    ret = l2fwd_parse_args(argc, argv);
+    if (ret < 0)
+        rte_exit(EXIT_FAILURE, "Invalid L2FWD arguments\n");
+
+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:
+
+.. code-block:: c
+
+    /* create the mbuf pool */
+    l2fwd_pktmbuf_pool =
+        rte_mempool_create("mbuf_pool", NB_MBUF,
+                   MBUF_SIZE, 32,
+                   sizeof(struct rte_pktmbuf_pool_private),
+                   rte_pktmbuf_pool_init, NULL,
+                   rte_pktmbuf_init, NULL,
+                   rte_socket_id(), 0);
+
+    if (l2fwd_pktmbuf_pool == NULL)
+        rte_exit(EXIT_FAILURE, "Cannot init mbuf pool\n");
+
+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,
+which expects to have some reserved space in the mempool structure,
+sizeof(struct rte_pktmbuf_pool_private) bytes.
+The number of allocated pkt mbufs is NB_MBUF, with a size of MBUF_SIZE each.
+A per-lcore cache of 32 mbufs is kept.
+The memory is allocated in rte_socket_id() socket,
+but it is possible to extend this code to allocate one mbuf pool per socket.
+
+Two callback pointers are also given to the rte_mempool_create() function:
+
+*   The first callback pointer is to rte_pktmbuf_pool_init() and is used
+    to initialize the private data of the mempool, which is needed by the driver.
+    This function is provided by the mbuf API, but can be copied and extended by the developer.
+
+*   The second callback pointer given to rte_mempool_create() is the mbuf initializer.
+    The default is used, that is, rte_pktmbuf_init(), which is provided in the rte_mbuf library.
+    If a more complex application wants to extend the rte_pktmbuf structure for its own needs,
+    a new function derived from rte_pktmbuf_init( ) can be created.
+
+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 that related to the Poll Mode Driver
+in the *DPDK Programmer's Guide* and the *DPDK API Reference*.
+
+.. code-block:: c
+
+    nb_ports = rte_eth_dev_count();
+
+    if (nb_ports == 0)
+        rte_exit(EXIT_FAILURE, "No Ethernet ports - bye\n");
+
+    if (nb_ports > RTE_MAX_ETHPORTS)
+        nb_ports = RTE_MAX_ETHPORTS;
+
+    /* reset l2fwd_dst_ports */
+
+    for (portid = 0; portid < RTE_MAX_ETHPORTS; portid++)
+        l2fwd_dst_ports[portid] = 0;
+
+    last_port = 0;
+
+    /*
+     * Each logical core is assigned a dedicated TX queue on each port.
+     */
+    for (portid = 0; portid < nb_ports; portid++) {
+        /* skip ports that are not enabled */
+        if ((l2fwd_enabled_port_mask & (1 << portid)) == 0)
+           continue;
+
+        if (nb_ports_in_mask % 2) {
+            l2fwd_dst_ports[portid] = last_port;
+            l2fwd_dst_ports[last_port] = portid;
+        }
+        else
+           last_port = portid;
+
+        nb_ports_in_mask++;
+
+        rte_eth_dev_info_get((uint8_t) portid, &dev_info);
+    }
+
+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:
+
+.. code-block:: c
+
+    ret = rte_eth_dev_configure((uint8_t)portid, 1, 1, &port_conf);
+    if (ret < 0)
+        rte_exit(EXIT_FAILURE, "Cannot configure device: "
+            "err=%d, port=%u\n",
+            ret, portid);
+
+The global configuration is stored in a static structure:
+
+.. code-block:: c
+
+    static const struct rte_eth_conf port_conf = {
+        .rxmode = {
+            .split_hdr_size = 0,
+            .header_split = 0,   /**< Header Split disabled */
+            .hw_ip_checksum = 0, /**< IP checksum offload disabled */
+            .hw_vlan_filter = 0, /**< VLAN filtering disabled */
+            .jumbo_frame = 0,    /**< Jumbo Frame Support disabled */
+            .hw_strip_crc= 0,    /**< CRC stripped by hardware */
+        },
+
+        .txmode = {
+            .mq_mode = ETH_DCB_NONE
+        },
+    };
+
+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.
+
+.. code-block:: c
+
+    ret = rte_eth_rx_queue_setup(portid, 0, nb_rxd,
+                rte_eth_dev_socket_id(portid),
+                NULL,
+                l2fwd_pktmbuf_pool);
+
+    if (ret < 0)
+        rte_exit(EXIT_FAILURE, "rte_eth_rx_queue_setup:err=%d, port=%u\n",
+                ret, (unsigned) portid);
+
+The list of queues that must be polled for a given lcore is stored in a private structure called struct lcore_queue_conf.
+
+.. code-block:: c
+
+    struct lcore_queue_conf {
+        unsigned n_rx_port;
+        unsigned rx_port_list[MAX_RX_QUEUE_PER_LCORE];
+        truct mbuf_table tx_mbufs[RTE_MAX_ETHPORTS];
+
+        struct rte_timer rx_timers[MAX_RX_QUEUE_PER_LCORE];
+        struct rte_jobstats port_fwd_jobs[MAX_RX_QUEUE_PER_LCORE];
+
+        struct rte_timer flush_timer;
+        struct rte_jobstats flush_job;
+        struct rte_jobstats idle_job;
+        struct rte_jobstats_context jobs_context;
+
+        rte_atomic16_t stats_read_pending;
+        rte_spinlock_t lock;
+    } __rte_cache_aligned;
+
+Values of struct lcore_queue_conf:
+
+*   n_rx_port and rx_port_list[] are used in the main packet processing loop
+    (see Section 9.4.6 "Receive, Process and Transmit Packets" later in this chapter).
+
+*   rx_timers and flush_timer are used to ensure forced TX on low packet rate.
+
+*   flush_job, idle_job and jobs_context are librte_jobstats objects used for managing l2fwd jobs.
+
+*   stats_read_pending and lock are used during job stats read phase.
+
+TX Queue Initialization
+~~~~~~~~~~~~~~~~~~~~~~~
+
+Each lcore should be able to transmit on any port. For every port, a single TX queue is initialized.
+
+.. code-block:: c
+
+    /* init one TX queue on each port */
+
+    fflush(stdout);
+    ret = rte_eth_tx_queue_setup(portid, 0, nb_txd,
+            rte_eth_dev_socket_id(portid),
+            NULL);
+    if (ret < 0)
+        rte_exit(EXIT_FAILURE, "rte_eth_tx_queue_setup:err=%d, port=%u\n",
+                ret, (unsigned) portid);
+
+Jobs statistics initialization
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+There are several statistics objects available:
+
+*   Flush job statistics
+
+.. code-block:: c
+
+    rte_jobstats_init(&qconf->flush_job, "flush", drain_tsc, drain_tsc,
+            drain_tsc, 0);
+
+    rte_timer_init(&qconf->flush_timer);
+    ret = rte_timer_reset(&qconf->flush_timer, drain_tsc, PERIODICAL,
+                lcore_id, &l2fwd_flush_job, NULL);
+
+    if (ret < 0) {
+        rte_exit(1, "Failed to reset flush job timer for lcore %u: %s",
+                    lcore_id, rte_strerror(-ret));
+    }
+
+*   Statistics per RX port
+
+.. code-block:: c
+
+    rte_jobstats_init(job, name, 0, drain_tsc, 0, MAX_PKT_BURST);
+    rte_jobstats_set_update_period_function(job, l2fwd_job_update_cb);
+
+    rte_timer_init(&qconf->rx_timers[i]);
+    ret = rte_timer_reset(&qconf->rx_timers[i], 0, PERIODICAL, lcore_id,
+            l2fwd_fwd_job, (void *)(uintptr_t)i);
+
+    if (ret < 0) {
+        rte_exit(1, "Failed to reset lcore %u port %u job timer: %s",
+                    lcore_id, qconf->rx_port_list[i], rte_strerror(-ret));
+    }
+
+Following parameters are passed to rte_jobstats_init():
+
+*   0 as minimal poll period
+
+*   drain_tsc as maximum poll period
+
+*   MAX_PKT_BURST as desired target value (RX burst size)
+
+Main loop
+~~~~~~~~~
+
+The forwarding path is reworked comparing to original L2 Forwarding application.
+In the l2fwd_main_loop() function three loops are placed.
+
+.. code-block:: c
+
+    for (;;) {
+        rte_spinlock_lock(&qconf->lock);
+
+        do {
+            rte_jobstats_context_start(&qconf->jobs_context);
+
+            /* Do the Idle job:
+             * - Read stats_read_pending flag
+             * - check if some real job need to be executed
+             */
+            rte_jobstats_start(&qconf->jobs_context, &qconf->idle_job);
+
+            do {
+                uint8_t i;
+                uint64_t now = rte_get_timer_cycles();
+
+                need_manage = qconf->flush_timer.expire < now;
+                /* Check if we was esked to give a stats. */
+                stats_read_pending =
+                        rte_atomic16_read(&qconf->stats_read_pending);
+                need_manage |= stats_read_pending;
+
+                for (i = 0; i < qconf->n_rx_port && !need_manage; i++)
+                    need_manage = qconf->rx_timers[i].expire < now;
+
+            } while (!need_manage);
+            rte_jobstats_finish(&qconf->idle_job, qconf->idle_job.target);
+
+            rte_timer_manage();
+            rte_jobstats_context_finish(&qconf->jobs_context);
+        } while (likely(stats_read_pending == 0));
+
+        rte_spinlock_unlock(&qconf->lock);
+        rte_pause();
+    }
+
+First inifnite for loop is to minimize impact of stats reading. Lock is only locked/unlocked when asked.
+
+Second inner while loop do the whole jobs management. When any job is ready, the use rte_timer_manage() is used to call the job handler.
+In this place functions l2fwd_fwd_job() and l2fwd_flush_job() are called when needed.
+Then rte_jobstats_context_finish() is called to mark loop end - no other jobs are ready to execute. By this time stats are ready to be read
+and if stats_read_pending is set, loop breaks allowing stats to be read.
+
+Third do-while loop is the idle job (idle stats counter). Its only purpose is moniting if any job is ready or stats job read is pending
+for this lcore. Statistics from this part of code is considered as the headroom available fo additional processing.
+
+Receive, Process and Transmit Packets
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The main task of l2fwd_fwd_job() function is to read ingress packets from the RX queue of particular port and forward it.
+This is done using the following code:
+
+.. code-block:: c
+
+    total_nb_rx = rte_eth_rx_burst((uint8_t) portid, 0, pkts_burst,
+            MAX_PKT_BURST);
+
+    for (j = 0; j < total_nb_rx; j++) {
+        m = pkts_burst[j];
+        rte_prefetch0(rte_pktmbuf_mtod(m, void *));
+        l2fwd_simple_forward(m, portid);
+    }
+
+Packets are read in a burst of size MAX_PKT_BURST.
+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.
+
+The rte_eth_rx_burst() function writes the mbuf pointers in a local table and returns the number of available mbufs in the table.
+
+After first read second try is issued.
+
+.. code::
+
+    if (total_nb_rx == MAX_PKT_BURST) {
+        const uint16_t nb_rx = rte_eth_rx_burst((uint8_t) portid, 0, pkts_burst,
+                MAX_PKT_BURST);
+
+        total_nb_rx += nb_rx;
+        for (j = 0; j < nb_rx; j++) {
+            m = pkts_burst[j];
+            rte_prefetch0(rte_pktmbuf_mtod(m, void *));
+            l2fwd_simple_forward(m, portid);
+        }
+    }
+
+This second read is important to give job stats library a feedback how many packets was processed.
+
+.. code::
+
+    /* Adjust period time in which we are running here. */
+    if (rte_jobstats_finish(job, total_nb_rx) != 0) {
+        rte_timer_reset(&qconf->rx_timers[port_idx], job->period, PERIODICAL,
+                lcore_id, l2fwd_fwd_job, arg);
+    }
+
+To maximize performance exactly MAX_PKT_BURST is expected (the target value) to be read for each l2fwd_fwd_job() call.
+If total_nb_rx is smaller than target value job->period will be increased. If it is greater the period will be decreased.
+
+.. note::
+
+    In the following code, one line for getting the output port requires some explanation.
+
+During the initialization process, a static array of destination ports (l2fwd_dst_ports[]) is filled such that for each source port,
+a destination port is assigned that is either the next or previous enabled port from the portmask.
+Naturally, the number of ports in the portmask must be even, otherwise, the application exits.
+
+.. code-block:: c
+
+    static void
+    l2fwd_simple_forward(struct rte_mbuf *m, unsigned portid)
+    {
+        struct ether_hdr *eth;
+        void *tmp;
+        unsigned dst_port;
+
+        dst_port = l2fwd_dst_ports[portid];
+
+        eth = rte_pktmbuf_mtod(m, struct ether_hdr *);
+
+        /* 02:00:00:00:00:xx */
+
+        tmp = &eth->d_addr.addr_bytes[0];
+
+        *((uint64_t *)tmp) = 0x000000000002 + ((uint64_t) dst_port << 40);
+
+        /* src addr */
+
+        ether_addr_copy(&l2fwd_ports_eth_addr[dst_port], &eth->s_addr);
+
+        l2fwd_send_packet(m, (uint8_t) dst_port);
+    }
+
+Then, the packet is sent using the l2fwd_send_packet (m, dst_port) function.
+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 l2fwd_send_burst() 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 that, so the same approach can be reused in a more complex application.
+
+The l2fwd_send_packet() function stores the packet in a per-lcore and per-txport table.
+If the table is full, the whole packets table is transmitted using the l2fwd_send_burst() function:
+
+.. code-block:: c
+
+    /* Send the packet on an output interface */
+
+    static int
+    l2fwd_send_packet(struct rte_mbuf *m, uint8_t port)
+    {
+        unsigned lcore_id, len;
+        struct lcore_queue_conf *qconf;
+
+        lcore_id = rte_lcore_id();
+        qconf = &lcore_queue_conf[lcore_id];
+        len = qconf->tx_mbufs[port].len;
+        qconf->tx_mbufs[port].m_table[len] = m;
+        len++;
+
+        /* enough pkts to be sent */
+
+        if (unlikely(len == MAX_PKT_BURST)) {
+            l2fwd_send_burst(qconf, MAX_PKT_BURST, port);
+            len = 0;
+        }
+
+        qconf->tx_mbufs[port].len = len; return 0;
+    }
+
+To ensure that no packets remain in the tables, the flush job exists. The l2fwd_flush_job()
+is called periodicaly to for each lcore draining TX queue of each port.
+This technique introduces some latency when there are not many packets to send,
+however it improves performance:
+
+.. code-block:: c
+
+    static void
+    l2fwd_flush_job(__rte_unused struct rte_timer *timer, __rte_unused void *arg)
+    {
+        uint64_t now;
+        unsigned lcore_id;
+        struct lcore_queue_conf *qconf;
+        struct mbuf_table *m_table;
+        uint8_t portid;
+
+        lcore_id = rte_lcore_id();
+        qconf = &lcore_queue_conf[lcore_id];
+
+        rte_jobstats_start(&qconf->jobs_context, &qconf->flush_job);
+
+        now = rte_get_timer_cycles();
+        lcore_id = rte_lcore_id();
+        qconf = &lcore_queue_conf[lcore_id];
+        for (portid = 0; portid < RTE_MAX_ETHPORTS; portid++) {
+            m_table = &qconf->tx_mbufs[portid];
+            if (m_table->len == 0 || m_table->next_flush_time <= now)
+                continue;
+
+            l2fwd_send_burst(qconf, portid);
+        }
+
+
+        /* Pass target to indicate that this job is happy of time interval
+         * in which it was called. */
+        rte_jobstats_finish(&qconf->flush_job, qconf->flush_job.target);
+    }
+
+.. |l2_fwd_benchmark_setup| image:: img/l2_fwd_benchmark_setup.svg
+
+.. |l2_fwd_virtenv_benchmark_setup| image:: img/l2_fwd_virtenv_benchmark_setup.png