X-Git-Url: http://git.droids-corp.org/?a=blobdiff_plain;f=doc%2Fguides%2Fprog_guide%2Fpoll_mode_drv.rst;h=d1d4b1cb743b69a664b4679f6df1e5926c0c0256;hb=7db274b9ada2221acb7110204a3b2c6a37d2614a;hp=bf3ea9fde25aa1706db398d23e3e22bd988e08ee;hpb=d085232a14bc40451aecdcf490abedcb85b438b7;p=dpdk.git diff --git a/doc/guides/prog_guide/poll_mode_drv.rst b/doc/guides/prog_guide/poll_mode_drv.rst index bf3ea9fde2..d1d4b1cb74 100644 --- a/doc/guides/prog_guide/poll_mode_drv.rst +++ b/doc/guides/prog_guide/poll_mode_drv.rst @@ -84,7 +84,7 @@ Whenever needed and appropriate, asynchronous communication should be introduced Avoiding lock contention is a key issue in a multi-core environment. To address this issue, PMDs are designed to work with per-core private resources as much as possible. -For example, a PMD maintains a separate transmit queue per-core, per-port. +For example, a PMD maintains a separate transmit queue per-core, per-port, if the PMD is not ``DEV_TX_OFFLOAD_MT_LOCKFREE`` capable. In the same way, every receive queue of a port is assigned to and polled by a single logical core (lcore). To comply with Non-Uniform Memory Access (NUMA), memory management is designed to assign to each logical core @@ -146,6 +146,16 @@ This is also true for the pipe-line model provided all logical cores used are lo Multiple logical cores should never share receive or transmit queues for interfaces since this would require global locks and hinder performance. +If the PMD is ``DEV_TX_OFFLOAD_MT_LOCKFREE`` capable, multiple threads can invoke ``rte_eth_tx_burst()`` +concurrently on the same tx queue without SW lock. This PMD feature found in some NICs and useful in the following use cases: + +* Remove explicit spinlock in some applications where lcores are not mapped to Tx queues with 1:1 relation. + +* In the eventdev use case, avoid dedicating a separate TX core for transmitting and thus + enables more scaling as all workers can send the packets. + +See `Hardware Offload`_ for ``DEV_TX_OFFLOAD_MT_LOCKFREE`` capability probing details. + Device Identification and Configuration --------------------------------------- @@ -200,8 +210,8 @@ Ethernet* flow control (pause frame) can be configured on the individual port. Refer to the testpmd source code for details. Also, L4 (UDP/TCP/ SCTP) checksum offload by the NIC can be enabled for an individual packet as long as the packet mbuf is set up correctly. See `Hardware Offload`_ for details. -Configuration of Transmit and Receive Queues -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Configuration of Transmit Queues +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Each transmit queue is independently configured with the following information: @@ -249,12 +259,49 @@ One descriptor in the TX ring is used as a sentinel to avoid a hardware race con When configuring for DCB operation, at port initialization, both the number of transmit queues and the number of receive queues must be set to 128. +Free Tx mbuf on Demand +~~~~~~~~~~~~~~~~~~~~~~ + +Many of the drivers do not release the mbuf back to the mempool, or local cache, +immediately after the packet has been transmitted. +Instead, they leave the mbuf in their Tx ring and +either perform a bulk release when the ``tx_rs_thresh`` has been crossed +or free the mbuf when a slot in the Tx ring is needed. + +An application can request the driver to release used mbufs with the ``rte_eth_tx_done_cleanup()`` API. +This API requests the driver to release mbufs that are no longer in use, +independent of whether or not the ``tx_rs_thresh`` has been crossed. +There are two scenarios when an application may want the mbuf released immediately: + +* When a given packet needs to be sent to multiple destination interfaces + (either for Layer 2 flooding or Layer 3 multi-cast). + One option is to make a copy of the packet or a copy of the header portion that needs to be manipulated. + A second option is to transmit the packet and then poll the ``rte_eth_tx_done_cleanup()`` API + until the reference count on the packet is decremented. + Then the same packet can be transmitted to the next destination interface. + The application is still responsible for managing any packet manipulations needed + between the different destination interfaces, but a packet copy can be avoided. + This API is independent of whether the packet was transmitted or dropped, + only that the mbuf is no longer in use by the interface. + +* Some applications are designed to make multiple runs, like a packet generator. + For performance reasons and consistency between runs, + the application may want to reset back to an initial state + between each run, where all mbufs are returned to the mempool. + In this case, it can call the ``rte_eth_tx_done_cleanup()`` API + for each destination interface it has been using + to request it to release of all its used mbufs. + +To determine if a driver supports this API, check for the *Free Tx mbuf on demand* feature +in the *Network Interface Controller Drivers* document. + Hardware Offload ~~~~~~~~~~~~~~~~ Depending on driver capabilities advertised by ``rte_eth_dev_info_get()``, the PMD may support hardware offloading -feature like checksumming, TCP segmentation or VLAN insertion. +feature like checksumming, TCP segmentation, VLAN insertion or +lockfree multithreaded TX burst on the same TX queue. The support of these offload features implies the addition of dedicated status bit(s) and value field(s) into the rte_mbuf data structure, along @@ -263,6 +310,26 @@ exported by each PMD. The list of flags and their precise meaning is described in the mbuf API documentation and in the in :ref:`Mbuf Library `, section "Meta Information". +Per-Port and Per-Queue Offloads +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +In the DPDK offload API, offloads are divided into per-port and per-queue offloads. +The different offloads capabilities can be queried using ``rte_eth_dev_info_get()``. +Supported offloads can be either per-port or per-queue. + +Offloads are enabled using the existing ``DEV_TX_OFFLOAD_*`` or ``DEV_RX_OFFLOAD_*`` flags. +Per-port offload configuration is set using ``rte_eth_dev_configure``. +Per-queue offload configuration is set using ``rte_eth_rx_queue_setup`` and ``rte_eth_tx_queue_setup``. +To enable per-port offload, the offload should be set on both device configuration and queue setup. +In case of a mixed configuration the queue setup shall return with an error. +To enable per-queue offload, the offload can be set only on the queue setup. +Offloads which are not enabled are disabled by default. + +For an application to use the Tx offloads API it should set the ``ETH_TXQ_FLAGS_IGNORE`` flag in the ``txq_flags`` field located in ``rte_eth_txconf`` struct. +In such cases it is not required to set other flags in ``txq_flags``. +For an application to use the Rx offloads API it should set the ``ignore_offload_bitfield`` bit in the ``rte_eth_rxmode`` struct. +In such cases it is not required to set other bitfield offloads in the ``rxmode`` struct. + Poll Mode Driver API -------------------- @@ -298,24 +365,21 @@ The Ethernet device API exported by the Ethernet PMDs is described in the *DPDK Extended Statistics API ~~~~~~~~~~~~~~~~~~~~~~~ -The extended statistics API allows each individual PMD to expose a unique set -of statistics. Accessing these from application programs is done via two -functions: - -* ``rte_eth_xstats_get``: Fills in an array of ``struct rte_eth_xstat`` - with extended statistics. -* ``rte_eth_xstats_get_names``: Fills in an array of - ``struct rte_eth_xstat_name`` with extended statistic name lookup - information. - -Each ``struct rte_eth_xstat`` contains an identifier and value pair, and -each ``struct rte_eth_xstat_name`` contains a string. Each identifier -within the ``struct rte_eth_xstat`` lookup array must have a corresponding -entry in the ``struct rte_eth_xstat_name`` lookup array. Within the latter -the index of the entry is the identifier the string is associated with. -These identifiers, as well as the number of extended statistic exposed, must -remain constant during runtime. Note that extended statistic identifiers are +The extended statistics API allows a PMD to expose all statistics that are +available to it, including statistics that are unique to the device. +Each statistic has three properties ``name``, ``id`` and ``value``: + +* ``name``: A human readable string formatted by the scheme detailed below. +* ``id``: An integer that represents only that statistic. +* ``value``: A unsigned 64-bit integer that is the value of the statistic. + +Note that extended statistic identifiers are driver-specific, and hence might not be the same for different ports. +The API consists of various ``rte_eth_xstats_*()`` functions, and allows an +application to be flexible in how it retrieves statistics. + +Scheme for Human Readable Names +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ A naming scheme exists for the strings exposed to clients of the API. This is to allow scraping of the API for statistics of interest. The naming scheme uses @@ -356,3 +420,179 @@ Some additions in the metadata scheme are as follows: An example where queue numbers are used is as follows: ``tx_q7_bytes`` which indicates this statistic applies to queue number 7, and represents the number of transmitted bytes on that queue. + +API Design +^^^^^^^^^^ + +The xstats API uses the ``name``, ``id``, and ``value`` to allow performant +lookup of specific statistics. Performant lookup means two things; + +* No string comparisons with the ``name`` of the statistic in fast-path +* Allow requesting of only the statistics of interest + +The API ensures these requirements are met by mapping the ``name`` of the +statistic to a unique ``id``, which is used as a key for lookup in the fast-path. +The API allows applications to request an array of ``id`` values, so that the +PMD only performs the required calculations. Expected usage is that the +application scans the ``name`` of each statistic, and caches the ``id`` +if it has an interest in that statistic. On the fast-path, the integer can be used +to retrieve the actual ``value`` of the statistic that the ``id`` represents. + +API Functions +^^^^^^^^^^^^^ + +The API is built out of a small number of functions, which can be used to +retrieve the number of statistics and the names, IDs and values of those +statistics. + +* ``rte_eth_xstats_get_names_by_id()``: returns the names of the statistics. When given a + ``NULL`` parameter the function returns the number of statistics that are available. + +* ``rte_eth_xstats_get_id_by_name()``: Searches for the statistic ID that matches + ``xstat_name``. If found, the ``id`` integer is set. + +* ``rte_eth_xstats_get_by_id()``: Fills in an array of ``uint64_t`` values + with matching the provided ``ids`` array. If the ``ids`` array is NULL, it + returns all statistics that are available. + + +Application Usage +^^^^^^^^^^^^^^^^^ + +Imagine an application that wants to view the dropped packet count. If no +packets are dropped, the application does not read any other metrics for +performance reasons. If packets are dropped, the application has a particular +set of statistics that it requests. This "set" of statistics allows the app to +decide what next steps to perform. The following code-snippets show how the +xstats API can be used to achieve this goal. + +First step is to get all statistics names and list them: + +.. code-block:: c + + struct rte_eth_xstat_name *xstats_names; + uint64_t *values; + int len, i; + + /* Get number of stats */ + len = rte_eth_xstats_get_names_by_id(port_id, NULL, NULL, 0); + if (len < 0) { + printf("Cannot get xstats count\n"); + goto err; + } + + xstats_names = malloc(sizeof(struct rte_eth_xstat_name) * len); + if (xstats_names == NULL) { + printf("Cannot allocate memory for xstat names\n"); + goto err; + } + + /* Retrieve xstats names, passing NULL for IDs to return all statistics */ + if (len != rte_eth_xstats_get_names_by_id(port_id, xstats_names, NULL, len)) { + printf("Cannot get xstat names\n"); + goto err; + } + + values = malloc(sizeof(values) * len); + if (values == NULL) { + printf("Cannot allocate memory for xstats\n"); + goto err; + } + + /* Getting xstats values */ + if (len != rte_eth_xstats_get_by_id(port_id, NULL, values, len)) { + printf("Cannot get xstat values\n"); + goto err; + } + + /* Print all xstats names and values */ + for (i = 0; i < len; i++) { + printf("%s: %"PRIu64"\n", xstats_names[i].name, values[i]); + } + +The application has access to the names of all of the statistics that the PMD +exposes. The application can decide which statistics are of interest, cache the +ids of those statistics by looking up the name as follows: + +.. code-block:: c + + uint64_t id; + uint64_t value; + const char *xstat_name = "rx_errors"; + + if(!rte_eth_xstats_get_id_by_name(port_id, xstat_name, &id)) { + rte_eth_xstats_get_by_id(port_id, &id, &value, 1); + printf("%s: %"PRIu64"\n", xstat_name, value); + } + else { + printf("Cannot find xstats with a given name\n"); + goto err; + } + +The API provides flexibility to the application so that it can look up multiple +statistics using an array containing multiple ``id`` numbers. This reduces the +function call overhead of retrieving statistics, and makes lookup of multiple +statistics simpler for the application. + +.. code-block:: c + + #define APP_NUM_STATS 4 + /* application cached these ids previously; see above */ + uint64_t ids_array[APP_NUM_STATS] = {3,4,7,21}; + uint64_t value_array[APP_NUM_STATS]; + + /* Getting multiple xstats values from array of IDs */ + rte_eth_xstats_get_by_id(port_id, ids_array, value_array, APP_NUM_STATS); + + uint32_t i; + for(i = 0; i < APP_NUM_STATS; i++) { + printf("%d: %"PRIu64"\n", ids_array[i], value_array[i]); + } + + +This array lookup API for xstats allows the application create multiple +"groups" of statistics, and look up the values of those IDs using a single API +call. As an end result, the application is able to achieve its goal of +monitoring a single statistic ("rx_errors" in this case), and if that shows +packets being dropped, it can easily retrieve a "set" of statistics using the +IDs array parameter to ``rte_eth_xstats_get_by_id`` function. + +NIC Reset API +~~~~~~~~~~~~~ + +.. code-block:: c + + int rte_eth_dev_reset(uint16_t port_id); + +Sometimes a port has to be reset passively. For example when a PF is +reset, all its VFs should also be reset by the application to make them +consistent with the PF. A DPDK application also can call this function +to trigger a port reset. Normally, a DPDK application would invokes this +function when an RTE_ETH_EVENT_INTR_RESET event is detected. + +It is the duty of the PMD to trigger RTE_ETH_EVENT_INTR_RESET events and +the application should register a callback function to handle these +events. When a PMD needs to trigger a reset, it can trigger an +RTE_ETH_EVENT_INTR_RESET event. On receiving an RTE_ETH_EVENT_INTR_RESET +event, applications can handle it as follows: Stop working queues, stop +calling Rx and Tx functions, and then call rte_eth_dev_reset(). For +thread safety all these operations should be called from the same thread. + +For example when PF is reset, the PF sends a message to notify VFs of +this event and also trigger an interrupt to VFs. Then in the interrupt +service routine the VFs detects this notification message and calls +_rte_eth_dev_callback_process(dev, RTE_ETH_EVENT_INTR_RESET, NULL). +This means that a PF reset triggers an RTE_ETH_EVENT_INTR_RESET +event within VFs. The function _rte_eth_dev_callback_process() will +call the registered callback function. The callback function can trigger +the application to handle all operations the VF reset requires including +stopping Rx/Tx queues and calling rte_eth_dev_reset(). + +The rte_eth_dev_reset() itself is a generic function which only does +some hardware reset operations through calling dev_unint() and +dev_init(), and itself does not handle synchronization, which is handled +by application. + +The PMD itself should not call rte_eth_dev_reset(). The PMD can trigger +the application to handle reset event. It is duty of application to +handle all synchronization before it calls rte_eth_dev_reset().