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

[Butler, Siobhan A]

> -----Original Message-----
> From: Wodkowski, PawelX
> Sent: Wednesday, March 11, 2015 9:42 AM
> To: dev at dpdk.org
> Cc: Butler, Siobhan A
> Subject: [PATCH] doc: add l2fwd-jobstats user guide
> 
> Signed-off-by: Pawel Wodkowski <pawelx.wodkowski at intel.com>
> ---
>  doc/guides/sample_app_ug/index.rst                |   1 +
>  doc/guides/sample_app_ug/l2_forward_job_stats.rst | 637
> ++++++++++++++++++++++
>  2 files changed, 638 insertions(+)
>  create mode 100644 doc/guides/sample_app_ug/l2_forward_job_stats.rst
> 
> 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..76cea71
> --- /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 orginal 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 avalable
> 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 procesed.
> +
> +.. 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
> --
> 1.9.1
Acked-by Siobhan Butler <siobhan.a. butler at intel.com>