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diff --git a/src/spdk/dpdk/doc/guides/sample_app_ug/multi_process.rst b/src/spdk/dpdk/doc/guides/sample_app_ug/multi_process.rst new file mode 100644 index 000000000..f2a79a639 --- /dev/null +++ b/src/spdk/dpdk/doc/guides/sample_app_ug/multi_process.rst @@ -0,0 +1,323 @@ +.. SPDX-License-Identifier: BSD-3-Clause + Copyright(c) 2010-2014 Intel Corporation. + +.. _multi_process_app: + +Multi-process Sample Application +================================ + +This chapter describes the example applications for multi-processing that are included in the DPDK. + +Example Applications +-------------------- + +Building the Sample Applications +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The multi-process example applications are built in the same way as other sample applications, +and as documented in the *DPDK Getting Started Guide*. + + +To compile the sample application see :doc:`compiling`. + +The applications are located in the ``multi_process`` sub-directory. + +.. note:: + + If just a specific multi-process application needs to be built, + the final make command can be run just in that application's directory, + rather than at the top-level multi-process directory. + +Basic Multi-process Example +~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The examples/simple_mp folder in the DPDK release contains a basic example application to demonstrate how +two DPDK processes can work together using queues and memory pools to share information. + +Running the Application +^^^^^^^^^^^^^^^^^^^^^^^ + +To run the application, start one copy of the simple_mp binary in one terminal, +passing at least two cores in the coremask/corelist, as follows: + +.. code-block:: console + + ./build/simple_mp -l 0-1 -n 4 --proc-type=primary + +For the first DPDK process run, the proc-type flag can be omitted or set to auto, +since all DPDK processes will default to being a primary instance, +meaning they have control over the hugepage shared memory regions. +The process should start successfully and display a command prompt as follows: + +.. code-block:: console + + $ ./build/simple_mp -l 0-1 -n 4 --proc-type=primary + EAL: coremask set to 3 + EAL: Detected lcore 0 on socket 0 + EAL: Detected lcore 1 on socket 0 + EAL: Detected lcore 2 on socket 0 + EAL: Detected lcore 3 on socket 0 + ... + + EAL: Requesting 2 pages of size 1073741824 + EAL: Requesting 768 pages of size 2097152 + EAL: Ask a virtual area of 0x40000000 bytes + EAL: Virtual area found at 0x7ff200000000 (size = 0x40000000) + ... + + EAL: check igb_uio module + EAL: check module finished + EAL: Master core 0 is ready (tid=54e41820) + EAL: Core 1 is ready (tid=53b32700) + + Starting core 1 + + simple_mp > + +To run the secondary process to communicate with the primary process, +again run the same binary setting at least two cores in the coremask/corelist: + +.. code-block:: console + + ./build/simple_mp -l 2-3 -n 4 --proc-type=secondary + +When running a secondary process such as that shown above, the proc-type parameter can again be specified as auto. +However, omitting the parameter altogether will cause the process to try and start as a primary rather than secondary process. + +Once the process type is specified correctly, +the process starts up, displaying largely similar status messages to the primary instance as it initializes. +Once again, you will be presented with a command prompt. + +Once both processes are running, messages can be sent between them using the send command. +At any stage, either process can be terminated using the quit command. + +.. code-block:: console + + EAL: Master core 10 is ready (tid=b5f89820) EAL: Master core 8 is ready (tid=864a3820) + EAL: Core 11 is ready (tid=84ffe700) EAL: Core 9 is ready (tid=85995700) + Starting core 11 Starting core 9 + simple_mp > send hello_secondary simple_mp > core 9: Received 'hello_secondary' + simple_mp > core 11: Received 'hello_primary' simple_mp > send hello_primary + simple_mp > quit simple_mp > quit + +.. note:: + + If the primary instance is terminated, the secondary instance must also be shut-down and restarted after the primary. + This is necessary because the primary instance will clear and reset the shared memory regions on startup, + invalidating the secondary process's pointers. + The secondary process can be stopped and restarted without affecting the primary process. + +How the Application Works +^^^^^^^^^^^^^^^^^^^^^^^^^ + +The core of this example application is based on using two queues and a single memory pool in shared memory. +These three objects are created at startup by the primary process, +since the secondary process cannot create objects in memory as it cannot reserve memory zones, +and the secondary process then uses lookup functions to attach to these objects as it starts up. + +.. code-block:: c + + if (rte_eal_process_type() == RTE_PROC_PRIMARY){ + send_ring = rte_ring_create(_PRI_2_SEC, ring_size, SOCKET0, flags); + recv_ring = rte_ring_create(_SEC_2_PRI, ring_size, SOCKET0, flags); + message_pool = rte_mempool_create(_MSG_POOL, pool_size, string_size, pool_cache, priv_data_sz, NULL, NULL, NULL, NULL, SOCKET0, flags); + } else { + recv_ring = rte_ring_lookup(_PRI_2_SEC); + send_ring = rte_ring_lookup(_SEC_2_PRI); + message_pool = rte_mempool_lookup(_MSG_POOL); + } + +Note, however, that the named ring structure used as send_ring in the primary process is the recv_ring in the secondary process. + +Once the rings and memory pools are all available in both the primary and secondary processes, +the application simply dedicates two threads to sending and receiving messages respectively. +The receive thread simply dequeues any messages on the receive ring, prints them, +and frees the buffer space used by the messages back to the memory pool. +The send thread makes use of the command-prompt library to interactively request user input for messages to send. +Once a send command is issued by the user, a buffer is allocated from the memory pool, filled in with the message contents, +then enqueued on the appropriate rte_ring. + +Symmetric Multi-process Example +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The second example of DPDK multi-process support demonstrates how a set of processes can run in parallel, +with each process performing the same set of packet- processing operations. +(Since each process is identical in functionality to the others, +we refer to this as symmetric multi-processing, to differentiate it from asymmetric multi- processing - +such as a client-server mode of operation seen in the next example, +where different processes perform different tasks, yet co-operate to form a packet-processing system.) +The following diagram shows the data-flow through the application, using two processes. + +.. _figure_sym_multi_proc_app: + +.. figure:: img/sym_multi_proc_app.* + + Example Data Flow in a Symmetric Multi-process Application + + +As the diagram shows, each process reads packets from each of the network ports in use. +RSS is used to distribute incoming packets on each port to different hardware RX queues. +Each process reads a different RX queue on each port and so does not contend with any other process for that queue access. +Similarly, each process writes outgoing packets to a different TX queue on each port. + +Running the Application +^^^^^^^^^^^^^^^^^^^^^^^ + +As with the simple_mp example, the first instance of the symmetric_mp process must be run as the primary instance, +though with a number of other application- specific parameters also provided after the EAL arguments. +These additional parameters are: + +* -p <portmask>, where portmask is a hexadecimal bitmask of what ports on the system are to be used. + For example: -p 3 to use ports 0 and 1 only. + +* --num-procs <N>, where N is the total number of symmetric_mp instances that will be run side-by-side to perform packet processing. + This parameter is used to configure the appropriate number of receive queues on each network port. + +* --proc-id <n>, where n is a numeric value in the range 0 <= n < N (number of processes, specified above). + This identifies which symmetric_mp instance is being run, so that each process can read a unique receive queue on each network port. + +The secondary symmetric_mp instances must also have these parameters specified, +and the first two must be the same as those passed to the primary instance, or errors result. + +For example, to run a set of four symmetric_mp instances, running on lcores 1-4, +all performing level-2 forwarding of packets between ports 0 and 1, +the following commands can be used (assuming run as root): + +.. code-block:: console + + # ./build/symmetric_mp -l 1 -n 4 --proc-type=auto -- -p 3 --num-procs=4 --proc-id=0 + # ./build/symmetric_mp -l 2 -n 4 --proc-type=auto -- -p 3 --num-procs=4 --proc-id=1 + # ./build/symmetric_mp -l 3 -n 4 --proc-type=auto -- -p 3 --num-procs=4 --proc-id=2 + # ./build/symmetric_mp -l 4 -n 4 --proc-type=auto -- -p 3 --num-procs=4 --proc-id=3 + +.. note:: + + In the above example, the process type can be explicitly specified as primary or secondary, rather than auto. + When using auto, the first process run creates all the memory structures needed for all processes - + irrespective of whether it has a proc-id of 0, 1, 2 or 3. + +.. note:: + + For the symmetric multi-process example, since all processes work in the same manner, + once the hugepage shared memory and the network ports are initialized, + it is not necessary to restart all processes if the primary instance dies. + Instead, that process can be restarted as a secondary, + by explicitly setting the proc-type to secondary on the command line. + (All subsequent instances launched will also need this explicitly specified, + as auto-detection will detect no primary processes running and therefore attempt to re-initialize shared memory.) + +How the Application Works +^^^^^^^^^^^^^^^^^^^^^^^^^ + +The initialization calls in both the primary and secondary instances are the same for the most part, +calling the rte_eal_init(), 1 G and 10 G driver initialization and then probing devices. +Thereafter, the initialization done depends on whether the process is configured as a primary or secondary instance. + +In the primary instance, a memory pool is created for the packet mbufs and the network ports to be used are initialized - +the number of RX and TX queues per port being determined by the num-procs parameter passed on the command-line. +The structures for the initialized network ports are stored in shared memory and +therefore will be accessible by the secondary process as it initializes. + +.. code-block:: c + + if (num_ports & 1) + rte_exit(EXIT_FAILURE, "Application must use an even number of ports\n"); + + for(i = 0; i < num_ports; i++){ + if(proc_type == RTE_PROC_PRIMARY) + if (smp_port_init(ports[i], mp, (uint16_t)num_procs) < 0) + rte_exit(EXIT_FAILURE, "Error initializing ports\n"); + } + +In the secondary instance, rather than initializing the network ports, the port information exported by the primary process is used, +giving the secondary process access to the hardware and software rings for each network port. +Similarly, the memory pool of mbufs is accessed by doing a lookup for it by name: + +.. code-block:: c + + mp = (proc_type == RTE_PROC_SECONDARY) ? rte_mempool_lookup(_SMP_MBUF_POOL) : rte_mempool_create(_SMP_MBUF_POOL, NB_MBUFS, MBUF_SIZE, ... ) + +Once this initialization is complete, the main loop of each process, both primary and secondary, +is exactly the same - each process reads from each port using the queue corresponding to its proc-id parameter, +and writes to the corresponding transmit queue on the output port. + +Client-Server Multi-process Example +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The third example multi-process application included with the DPDK shows how one can +use a client-server type multi-process design to do packet processing. +In this example, a single server process performs the packet reception from the ports being used and +distributes these packets using round-robin ordering among a set of client processes, +which perform the actual packet processing. +In this case, the client applications just perform level-2 forwarding of packets by sending each packet out on a different network port. + +The following diagram shows the data-flow through the application, using two client processes. + +.. _figure_client_svr_sym_multi_proc_app: + +.. figure:: img/client_svr_sym_multi_proc_app.* + + Example Data Flow in a Client-Server Symmetric Multi-process Application + + +Running the Application +^^^^^^^^^^^^^^^^^^^^^^^ + +The server process must be run initially as the primary process to set up all memory structures for use by the clients. +In addition to the EAL parameters, the application- specific parameters are: + +* -p <portmask >, where portmask is a hexadecimal bitmask of what ports on the system are to be used. + For example: -p 3 to use ports 0 and 1 only. + +* -n <num-clients>, where the num-clients parameter is the number of client processes that will process the packets received + by the server application. + +.. note:: + + In the server process, a single thread, the master thread, that is, the lowest numbered lcore in the coremask/corelist, performs all packet I/O. + If a coremask/corelist is specified with more than a single lcore bit set in it, + an additional lcore will be used for a thread to periodically print packet count statistics. + +Since the server application stores configuration data in shared memory, including the network ports to be used, +the only application parameter needed by a client process is its client instance ID. +Therefore, to run a server application on lcore 1 (with lcore 2 printing statistics) along with two client processes running on lcores 3 and 4, +the following commands could be used: + +.. code-block:: console + + # ./mp_server/build/mp_server -l 1-2 -n 4 -- -p 3 -n 2 + # ./mp_client/build/mp_client -l 3 -n 4 --proc-type=auto -- -n 0 + # ./mp_client/build/mp_client -l 4 -n 4 --proc-type=auto -- -n 1 + +.. note:: + + If the server application dies and needs to be restarted, all client applications also need to be restarted, + as there is no support in the server application for it to run as a secondary process. + Any client processes that need restarting can be restarted without affecting the server process. + +How the Application Works +^^^^^^^^^^^^^^^^^^^^^^^^^ + +The server process performs the network port and data structure initialization much as the symmetric multi-process application does when run as primary. +One additional enhancement in this sample application is that the server process stores its port configuration data in a memory zone in hugepage shared memory. +This eliminates the need for the client processes to have the portmask parameter passed into them on the command line, +as is done for the symmetric multi-process application, and therefore eliminates mismatched parameters as a potential source of errors. + +In the same way that the server process is designed to be run as a primary process instance only, +the client processes are designed to be run as secondary instances only. +They have no code to attempt to create shared memory objects. +Instead, handles to all needed rings and memory pools are obtained via calls to rte_ring_lookup() and rte_mempool_lookup(). +The network ports for use by the processes are obtained by loading the network port drivers and probing the PCI bus, +which will, as in the symmetric multi-process example, +automatically get access to the network ports using the settings already configured by the primary/server process. + +Once all applications are initialized, the server operates by reading packets from each network port in turn and +distributing those packets to the client queues (software rings, one for each client process) in round-robin order. +On the client side, the packets are read from the rings in as big of bursts as possible, then routed out to a different network port. +The routing used is very simple. All packets received on the first NIC port are transmitted back out on the second port and vice versa. +Similarly, packets are routed between the 3rd and 4th network ports and so on. +The sending of packets is done by writing the packets directly to the network ports; they are not transferred back via the server process. + +In both the server and the client processes, outgoing packets are buffered before being sent, +so as to allow the sending of multiple packets in a single burst to improve efficiency. +For example, the client process will buffer packets to send, +until either the buffer is full or until we receive no further packets from the server. |