summaryrefslogtreecommitdiff
path: root/doc/guides/prog_guide/eventdev.rst
diff options
context:
space:
mode:
authorHarry van Haaren <harry.van.haaren@intel.com>2017-07-06 15:35:16 +0100
committerJerin Jacob <jerin.jacob@caviumnetworks.com>2017-07-07 09:30:35 +0200
commit7358c91ffa854710d6a4bf69009f657669e56553 (patch)
tree5dbd8db4c7f134953b54bd8bd1f4c4f441c66a1c /doc/guides/prog_guide/eventdev.rst
parent1094ca96689cc4c0c5671a827aaf9259e4f526c4 (diff)
downloaddpdk-7358c91ffa854710d6a4bf69009f657669e56553.zip
dpdk-7358c91ffa854710d6a4bf69009f657669e56553.tar.gz
dpdk-7358c91ffa854710d6a4bf69009f657669e56553.tar.xz
doc: add eventdev library to programmers guide
This commit adds an entry in the programmers guide explaining the eventdev library. The rte_event struct, queues and ports are explained. An API walktrough of a simple two stage atomic pipeline provides the reader with a step by step overview of the expected usage of the Eventdev API. Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com> Signed-off-by: David Hunt <david.hunt@intel.com> Acked-by: John McNamara <john.mcnamara@intel.com> Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Diffstat (limited to 'doc/guides/prog_guide/eventdev.rst')
-rw-r--r--doc/guides/prog_guide/eventdev.rst394
1 files changed, 394 insertions, 0 deletions
diff --git a/doc/guides/prog_guide/eventdev.rst b/doc/guides/prog_guide/eventdev.rst
new file mode 100644
index 0000000..908d123
--- /dev/null
+++ b/doc/guides/prog_guide/eventdev.rst
@@ -0,0 +1,394 @@
+.. BSD LICENSE
+ Copyright(c) 2017 Intel Corporation. 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.
+
+Event Device Library
+====================
+
+The DPDK Event device library is an abstraction that provides the application
+with features to schedule events. This is achieved using the PMD architecture
+similar to the ethdev or cryptodev APIs, which may already be familiar to the
+reader.
+
+The eventdev framework introduces the event driven programming model. In a
+polling model, lcores poll ethdev ports and associated Rx queues directly
+to look for a packet. By contrast in an event driven model, lcores call the
+scheduler that selects packets for them based on programmer-specified criteria.
+The Eventdev library adds support for an event driven programming model, which
+offers applications automatic multicore scaling, dynamic load balancing,
+pipelining, packet ingress order maintenance and synchronization services to
+simplify application packet processing.
+
+By introducing an event driven programming model, DPDK can support both polling
+and event driven programming models for packet processing, and applications are
+free to choose whatever model (or combination of the two) best suits their
+needs.
+
+Step-by-step instructions of the eventdev design is available in the `API
+Walk-through`_ section later in this document.
+
+Event struct
+------------
+
+The eventdev API represents each event with a generic struct, which contains a
+payload and metadata required for scheduling by an eventdev. The
+``rte_event`` struct is a 16 byte C structure, defined in
+``libs/librte_eventdev/rte_eventdev.h``.
+
+Event Metadata
+~~~~~~~~~~~~~~
+
+The rte_event structure contains the following metadata fields, which the
+application fills in to have the event scheduled as required:
+
+* ``flow_id`` - The targeted flow identifier for the enq/deq operation.
+* ``event_type`` - The source of this event, eg RTE_EVENT_TYPE_ETHDEV or CPU.
+* ``sub_event_type`` - Distinguishes events inside the application, that have
+ the same event_type (see above)
+* ``op`` - This field takes one of the RTE_EVENT_OP_* values, and tells the
+ eventdev about the status of the event - valid values are NEW, FORWARD or
+ RELEASE.
+* ``sched_type`` - Represents the type of scheduling that should be performed
+ on this event, valid values are the RTE_SCHED_TYPE_ORDERED, ATOMIC and
+ PARALLEL.
+* ``queue_id`` - The identifier for the event queue that the event is sent to.
+* ``priority`` - The priority of this event, see RTE_EVENT_DEV_PRIORITY.
+
+Event Payload
+~~~~~~~~~~~~~
+
+The rte_event struct contains a union for payload, allowing flexibility in what
+the actual event being scheduled is. The payload is a union of the following:
+
+* ``uint64_t u64``
+* ``void *event_ptr``
+* ``struct rte_mbuf *mbuf``
+
+These three items in a union occupy the same 64 bits at the end of the rte_event
+structure. The application can utilize the 64 bits directly by accessing the
+u64 variable, while the event_ptr and mbuf are provided as convenience
+variables. For example the mbuf pointer in the union can used to schedule a
+DPDK packet.
+
+Queues
+~~~~~~
+
+An event queue is a queue containing events that are scheduled by the event
+device. An event queue contains events of different flows associated with
+scheduling types, such as atomic, ordered, or parallel.
+
+Queue All Types Capable
+^^^^^^^^^^^^^^^^^^^^^^^
+
+If RTE_EVENT_DEV_CAP_QUEUE_ALL_TYPES capability bit is set in the event device,
+then events of any type may be sent to any queue. Otherwise, the queues only
+support events of the type that it was created with.
+
+Queue All Types Incapable
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+In this case, each stage has a specified scheduling type. The application
+configures each queue for a specific type of scheduling, and just enqueues all
+events to the eventdev. An example of a PMD of this type is the eventdev
+software PMD.
+
+The Eventdev API supports the following scheduling types per queue:
+
+* Atomic
+* Ordered
+* Parallel
+
+Atomic, Ordered and Parallel are load-balanced scheduling types: the output
+of the queue can be spread out over multiple CPU cores.
+
+Atomic scheduling on a queue ensures that a single flow is not present on two
+different CPU cores at the same time. Ordered allows sending all flows to any
+core, but the scheduler must ensure that on egress the packets are returned to
+ingress order on downstream queue enqueue. Parallel allows sending all flows
+to all CPU cores, without any re-ordering guarantees.
+
+Single Link Flag
+^^^^^^^^^^^^^^^^
+
+There is a SINGLE_LINK flag which allows an application to indicate that only
+one port will be connected to a queue. Queues configured with the single-link
+flag follow a FIFO like structure, maintaining ordering but it is only capable
+of being linked to a single port (see below for port and queue linking details).
+
+
+Ports
+~~~~~
+
+Ports are the points of contact between worker cores and the eventdev. The
+general use-case will see one CPU core using one port to enqueue and dequeue
+events from an eventdev. Ports are linked to queues in order to retrieve events
+from those queues (more details in `Linking Queues and Ports`_ below).
+
+
+API Walk-through
+----------------
+
+This section will introduce the reader to the eventdev API, showing how to
+create and configure an eventdev and use it for a two-stage atomic pipeline
+with a single core for TX. The diagram below shows the final state of the
+application after this walk-through:
+
+.. _figure_eventdev-usage1:
+
+.. figure:: img/eventdev_usage.*
+
+ Sample eventdev usage, with RX, two atomic stages and a single-link to TX.
+
+
+A high level overview of the setup steps are:
+
+* rte_event_dev_configure()
+* rte_event_queue_setup()
+* rte_event_port_setup()
+* rte_event_port_link()
+* rte_event_dev_start()
+
+
+Init and Config
+~~~~~~~~~~~~~~~
+
+The eventdev library uses vdev options to add devices to the DPDK application.
+The ``--vdev`` EAL option allows adding eventdev instances to your DPDK
+application, using the name of the eventdev PMD as an argument.
+
+For example, to create an instance of the software eventdev scheduler, the
+following vdev arguments should be provided to the application EAL command line:
+
+.. code-block:: console
+
+ ./dpdk_application --vdev="event_sw0"
+
+In the following code, we configure eventdev instance with 3 queues
+and 6 ports as follows. The 3 queues consist of 2 Atomic and 1 Single-Link,
+while the 6 ports consist of 4 workers, 1 RX and 1 TX.
+
+.. code-block:: c
+
+ const struct rte_event_dev_config config = {
+ .nb_event_queues = 3,
+ .nb_event_ports = 6,
+ .nb_events_limit = 4096,
+ .nb_event_queue_flows = 1024,
+ .nb_event_port_dequeue_depth = 128,
+ .nb_event_port_enqueue_depth = 128,
+ };
+ int err = rte_event_dev_configure(dev_id, &config);
+
+The remainder of this walk-through assumes that dev_id is 0.
+
+Setting up Queues
+~~~~~~~~~~~~~~~~~
+
+Once the eventdev itself is configured, the next step is to configure queues.
+This is done by setting the appropriate values in a queue_conf structure, and
+calling the setup function. Repeat this step for each queue, starting from
+0 and ending at ``nb_event_queues - 1`` from the event_dev config above.
+
+.. code-block:: c
+
+ struct rte_event_queue_conf atomic_conf = {
+ .event_queue_cfg = RTE_EVENT_QUEUE_CFG_ATOMIC_ONLY,
+ .priority = RTE_EVENT_DEV_PRIORITY_NORMAL,
+ .nb_atomic_flows = 1024,
+ .nb_atomic_order_sequences = 1024,
+ };
+ int dev_id = 0;
+ int queue_id = 0;
+ int err = rte_event_queue_setup(dev_id, queue_id, &atomic_conf);
+
+The remainder of this walk-through assumes that the queues are configured as
+follows:
+
+ * id 0, atomic queue #1
+ * id 1, atomic queue #2
+ * id 2, single-link queue
+
+Setting up Ports
+~~~~~~~~~~~~~~~~
+
+Once queues are set up successfully, create the ports as required. Each port
+should be set up with its corresponding port_conf type, worker for worker cores,
+rx and tx for the RX and TX cores:
+
+.. code-block:: c
+
+ struct rte_event_port_conf rx_conf = {
+ .dequeue_depth = 128,
+ .enqueue_depth = 128,
+ .new_event_threshold = 1024,
+ };
+ struct rte_event_port_conf worker_conf = {
+ .dequeue_depth = 16,
+ .enqueue_depth = 64,
+ .new_event_threshold = 4096,
+ };
+ struct rte_event_port_conf tx_conf = {
+ .dequeue_depth = 128,
+ .enqueue_depth = 128,
+ .new_event_threshold = 4096,
+ };
+ int dev_id = 0;
+ int port_id = 0;
+ int err = rte_event_port_setup(dev_id, port_id, &CORE_FUNCTION_conf);
+
+It is now assumed that:
+
+ * port 0: RX core
+ * ports 1,2,3,4: Workers
+ * port 5: TX core
+
+Linking Queues and Ports
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+The final step is to "wire up" the ports to the queues. After this, the
+eventdev is capable of scheduling events, and when cores request work to do,
+the correct events are provided to that core. Note that the RX core takes input
+from eg: a NIC so it is not linked to any eventdev queues.
+
+Linking all workers to atomic queues, and the TX core to the single-link queue
+can be achieved like this:
+
+.. code-block:: c
+
+ uint8_t port_id = 0;
+ uint8_t atomic_qs[] = {0, 1};
+ uint8_t single_link_q = 2;
+ uint8_t tx_port_id = 5;
+ uin8t_t priority = RTE_EVENT_DEV_PRIORITY_NORMAL;
+
+ for(int i = 0; i < 4; i++) {
+ int worker_port = i + 1;
+ int links_made = rte_event_port_link(dev_id, worker_port, atomic_qs, NULL, 2);
+ }
+ int links_made = rte_event_port_link(dev_id, tx_port_id, &single_link_q, &priority, 1);
+
+Starting the EventDev
+~~~~~~~~~~~~~~~~~~~~~
+
+A single function call tells the eventdev instance to start processing
+events. Note that all queues must be linked to for the instance to start, as
+if any queue is not linked to, enqueuing to that queue will cause the
+application to backpressure and eventually stall due to no space in the
+eventdev.
+
+.. code-block:: c
+
+ int err = rte_event_dev_start(dev_id);
+
+Ingress of New Events
+~~~~~~~~~~~~~~~~~~~~~
+
+Now that the eventdev is set up, and ready to receive events, the RX core must
+enqueue some events into the system for it to schedule. The events to be
+scheduled are ordinary DPDK packets, received from an eth_rx_burst() as normal.
+The following code shows how those packets can be enqueued into the eventdev:
+
+.. code-block:: c
+
+ const uint16_t nb_rx = rte_eth_rx_burst(eth_port, 0, mbufs, BATCH_SIZE);
+
+ for (i = 0; i < nb_rx; i++) {
+ ev[i].flow_id = mbufs[i]->hash.rss;
+ ev[i].op = RTE_EVENT_OP_NEW;
+ ev[i].sched_type = RTE_EVENT_QUEUE_CFG_ATOMIC_ONLY;
+ ev[i].queue_id = 0;
+ ev[i].event_type = RTE_EVENT_TYPE_ETHDEV;
+ ev[i].sub_event_type = 0;
+ ev[i].priority = RTE_EVENT_DEV_PRIORITY_NORMAL;
+ ev[i].mbuf = mbufs[i];
+ }
+
+ const int nb_tx = rte_event_enqueue_burst(dev_id, port_id, ev, nb_rx);
+ if (nb_tx != nb_rx) {
+ for(i = nb_tx; i < nb_rx; i++)
+ rte_pktmbuf_free(mbufs[i]);
+ }
+
+Forwarding of Events
+~~~~~~~~~~~~~~~~~~~~
+
+Now that the RX core has injected events, there is work to be done by the
+workers. Note that each worker will dequeue as many events as it can in a burst,
+process each one individually, and then burst the packets back into the
+eventdev.
+
+The worker can lookup the events source from ``event.queue_id``, which should
+indicate to the worker what workload needs to be performed on the event.
+Once done, the worker can update the ``event.queue_id`` to a new value, to send
+the event to the next stage in the pipeline.
+
+.. code-block:: c
+
+ int timeout = 0;
+ struct rte_event events[BATCH_SIZE];
+ uint16_t nb_rx = rte_event_dequeue_burst(dev_id, worker_port_id, events, BATCH_SIZE, timeout);
+
+ for (i = 0; i < nb_rx; i++) {
+ /* process mbuf using events[i].queue_id as pipeline stage */
+ struct rte_mbuf *mbuf = events[i].mbuf;
+ /* Send event to next stage in pipeline */
+ events[i].queue_id++;
+ }
+
+ uint16_t nb_tx = rte_event_enqueue_burst(dev_id, port_id, events, nb_rx);
+
+
+Egress of Events
+~~~~~~~~~~~~~~~~
+
+Finally, when the packet is ready for egress or needs to be dropped, we need
+to inform the eventdev that the packet is no longer being handled by the
+application. This can be done by calling dequeue() or dequeue_burst(), which
+indicates that the previous burst of packets is no longer in use by the
+application.
+
+An event driven worker thread has following typical workflow on fastpath:
+
+.. code-block:: c
+
+ while (1) {
+ rte_event_dequeue_burst(...);
+ (event processing)
+ rte_event_enqueue_burst(...);
+ }
+
+
+Summary
+-------
+
+The eventdev library allows an application to easily schedule events as it
+requires, either using a run-to-completion or pipeline processing model. The
+queues and ports abstract the logical functionality of an eventdev, providing
+the application with a generic method to schedule events. With the flexible
+PMD infrastructure applications benefit of improvements in existing eventdevs
+and additions of new ones without modification.