c86ced193a
Update the guide with event queue configuration and event enqueue operation. Signed-off-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com> Acked-by: Harry van Haaren <harry.van.haaren@intel.com>
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ReStructuredText
395 lines
15 KiB
ReStructuredText
.. BSD LICENSE
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Copyright(c) 2017 Intel Corporation. All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions
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are met:
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* Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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* Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in
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the documentation and/or other materials provided with the
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distribution.
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* Neither the name of Intel Corporation nor the names of its
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contributors may be used to endorse or promote products derived
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from this software without specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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Event Device Library
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====================
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The DPDK Event device library is an abstraction that provides the application
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with features to schedule events. This is achieved using the PMD architecture
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similar to the ethdev or cryptodev APIs, which may already be familiar to the
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reader.
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The eventdev framework introduces the event driven programming model. In a
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polling model, lcores poll ethdev ports and associated Rx queues directly
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to look for a packet. By contrast in an event driven model, lcores call the
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scheduler that selects packets for them based on programmer-specified criteria.
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The Eventdev library adds support for an event driven programming model, which
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offers applications automatic multicore scaling, dynamic load balancing,
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pipelining, packet ingress order maintenance and synchronization services to
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simplify application packet processing.
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By introducing an event driven programming model, DPDK can support both polling
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and event driven programming models for packet processing, and applications are
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free to choose whatever model (or combination of the two) best suits their
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needs.
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Step-by-step instructions of the eventdev design is available in the `API
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Walk-through`_ section later in this document.
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Event struct
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------------
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The eventdev API represents each event with a generic struct, which contains a
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payload and metadata required for scheduling by an eventdev. The
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``rte_event`` struct is a 16 byte C structure, defined in
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``libs/librte_eventdev/rte_eventdev.h``.
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Event Metadata
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~~~~~~~~~~~~~~
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The rte_event structure contains the following metadata fields, which the
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application fills in to have the event scheduled as required:
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* ``flow_id`` - The targeted flow identifier for the enq/deq operation.
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* ``event_type`` - The source of this event, eg RTE_EVENT_TYPE_ETHDEV or CPU.
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* ``sub_event_type`` - Distinguishes events inside the application, that have
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the same event_type (see above)
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* ``op`` - This field takes one of the RTE_EVENT_OP_* values, and tells the
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eventdev about the status of the event - valid values are NEW, FORWARD or
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RELEASE.
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* ``sched_type`` - Represents the type of scheduling that should be performed
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on this event, valid values are the RTE_SCHED_TYPE_ORDERED, ATOMIC and
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PARALLEL.
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* ``queue_id`` - The identifier for the event queue that the event is sent to.
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* ``priority`` - The priority of this event, see RTE_EVENT_DEV_PRIORITY.
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Event Payload
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~~~~~~~~~~~~~
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The rte_event struct contains a union for payload, allowing flexibility in what
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the actual event being scheduled is. The payload is a union of the following:
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* ``uint64_t u64``
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* ``void *event_ptr``
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* ``struct rte_mbuf *mbuf``
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These three items in a union occupy the same 64 bits at the end of the rte_event
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structure. The application can utilize the 64 bits directly by accessing the
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u64 variable, while the event_ptr and mbuf are provided as convenience
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variables. For example the mbuf pointer in the union can used to schedule a
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DPDK packet.
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Queues
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~~~~~~
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An event queue is a queue containing events that are scheduled by the event
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device. An event queue contains events of different flows associated with
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scheduling types, such as atomic, ordered, or parallel.
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Queue All Types Capable
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^^^^^^^^^^^^^^^^^^^^^^^
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If RTE_EVENT_DEV_CAP_QUEUE_ALL_TYPES capability bit is set in the event device,
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then events of any type may be sent to any queue. Otherwise, the queues only
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support events of the type that it was created with.
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Queue All Types Incapable
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^^^^^^^^^^^^^^^^^^^^^^^^^
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In this case, each stage has a specified scheduling type. The application
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configures each queue for a specific type of scheduling, and just enqueues all
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events to the eventdev. An example of a PMD of this type is the eventdev
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software PMD.
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The Eventdev API supports the following scheduling types per queue:
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* Atomic
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* Ordered
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* Parallel
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Atomic, Ordered and Parallel are load-balanced scheduling types: the output
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of the queue can be spread out over multiple CPU cores.
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Atomic scheduling on a queue ensures that a single flow is not present on two
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different CPU cores at the same time. Ordered allows sending all flows to any
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core, but the scheduler must ensure that on egress the packets are returned to
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ingress order on downstream queue enqueue. Parallel allows sending all flows
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to all CPU cores, without any re-ordering guarantees.
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Single Link Flag
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^^^^^^^^^^^^^^^^
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There is a SINGLE_LINK flag which allows an application to indicate that only
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one port will be connected to a queue. Queues configured with the single-link
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flag follow a FIFO like structure, maintaining ordering but it is only capable
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of being linked to a single port (see below for port and queue linking details).
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Ports
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~~~~~
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Ports are the points of contact between worker cores and the eventdev. The
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general use-case will see one CPU core using one port to enqueue and dequeue
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events from an eventdev. Ports are linked to queues in order to retrieve events
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from those queues (more details in `Linking Queues and Ports`_ below).
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API Walk-through
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----------------
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This section will introduce the reader to the eventdev API, showing how to
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create and configure an eventdev and use it for a two-stage atomic pipeline
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with a single core for TX. The diagram below shows the final state of the
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application after this walk-through:
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.. _figure_eventdev-usage1:
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.. figure:: img/eventdev_usage.*
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Sample eventdev usage, with RX, two atomic stages and a single-link to TX.
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A high level overview of the setup steps are:
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* rte_event_dev_configure()
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* rte_event_queue_setup()
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* rte_event_port_setup()
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* rte_event_port_link()
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* rte_event_dev_start()
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Init and Config
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~~~~~~~~~~~~~~~
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The eventdev library uses vdev options to add devices to the DPDK application.
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The ``--vdev`` EAL option allows adding eventdev instances to your DPDK
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application, using the name of the eventdev PMD as an argument.
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For example, to create an instance of the software eventdev scheduler, the
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following vdev arguments should be provided to the application EAL command line:
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.. code-block:: console
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./dpdk_application --vdev="event_sw0"
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In the following code, we configure eventdev instance with 3 queues
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and 6 ports as follows. The 3 queues consist of 2 Atomic and 1 Single-Link,
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while the 6 ports consist of 4 workers, 1 RX and 1 TX.
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.. code-block:: c
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const struct rte_event_dev_config config = {
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.nb_event_queues = 3,
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.nb_event_ports = 6,
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.nb_events_limit = 4096,
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.nb_event_queue_flows = 1024,
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.nb_event_port_dequeue_depth = 128,
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.nb_event_port_enqueue_depth = 128,
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};
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int err = rte_event_dev_configure(dev_id, &config);
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The remainder of this walk-through assumes that dev_id is 0.
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Setting up Queues
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~~~~~~~~~~~~~~~~~
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Once the eventdev itself is configured, the next step is to configure queues.
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This is done by setting the appropriate values in a queue_conf structure, and
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calling the setup function. Repeat this step for each queue, starting from
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0 and ending at ``nb_event_queues - 1`` from the event_dev config above.
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.. code-block:: c
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struct rte_event_queue_conf atomic_conf = {
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.schedule_type = RTE_SCHED_TYPE_ATOMIC,
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.priority = RTE_EVENT_DEV_PRIORITY_NORMAL,
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.nb_atomic_flows = 1024,
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.nb_atomic_order_sequences = 1024,
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};
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int dev_id = 0;
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int queue_id = 0;
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int err = rte_event_queue_setup(dev_id, queue_id, &atomic_conf);
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The remainder of this walk-through assumes that the queues are configured as
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follows:
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* id 0, atomic queue #1
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* id 1, atomic queue #2
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* id 2, single-link queue
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Setting up Ports
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~~~~~~~~~~~~~~~~
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Once queues are set up successfully, create the ports as required. Each port
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should be set up with its corresponding port_conf type, worker for worker cores,
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rx and tx for the RX and TX cores:
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.. code-block:: c
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struct rte_event_port_conf rx_conf = {
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.dequeue_depth = 128,
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.enqueue_depth = 128,
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.new_event_threshold = 1024,
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};
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struct rte_event_port_conf worker_conf = {
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.dequeue_depth = 16,
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.enqueue_depth = 64,
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.new_event_threshold = 4096,
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};
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struct rte_event_port_conf tx_conf = {
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.dequeue_depth = 128,
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.enqueue_depth = 128,
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.new_event_threshold = 4096,
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};
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int dev_id = 0;
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int port_id = 0;
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int err = rte_event_port_setup(dev_id, port_id, &CORE_FUNCTION_conf);
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It is now assumed that:
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* port 0: RX core
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* ports 1,2,3,4: Workers
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* port 5: TX core
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Linking Queues and Ports
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~~~~~~~~~~~~~~~~~~~~~~~~
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The final step is to "wire up" the ports to the queues. After this, the
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eventdev is capable of scheduling events, and when cores request work to do,
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the correct events are provided to that core. Note that the RX core takes input
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from eg: a NIC so it is not linked to any eventdev queues.
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Linking all workers to atomic queues, and the TX core to the single-link queue
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can be achieved like this:
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.. code-block:: c
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uint8_t port_id = 0;
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uint8_t atomic_qs[] = {0, 1};
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uint8_t single_link_q = 2;
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uint8_t tx_port_id = 5;
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uin8t_t priority = RTE_EVENT_DEV_PRIORITY_NORMAL;
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for(int i = 0; i < 4; i++) {
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int worker_port = i + 1;
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int links_made = rte_event_port_link(dev_id, worker_port, atomic_qs, NULL, 2);
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}
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int links_made = rte_event_port_link(dev_id, tx_port_id, &single_link_q, &priority, 1);
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Starting the EventDev
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~~~~~~~~~~~~~~~~~~~~~
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A single function call tells the eventdev instance to start processing
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events. Note that all queues must be linked to for the instance to start, as
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if any queue is not linked to, enqueuing to that queue will cause the
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application to backpressure and eventually stall due to no space in the
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eventdev.
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.. code-block:: c
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int err = rte_event_dev_start(dev_id);
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Ingress of New Events
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~~~~~~~~~~~~~~~~~~~~~
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Now that the eventdev is set up, and ready to receive events, the RX core must
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enqueue some events into the system for it to schedule. The events to be
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scheduled are ordinary DPDK packets, received from an eth_rx_burst() as normal.
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The following code shows how those packets can be enqueued into the eventdev:
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.. code-block:: c
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const uint16_t nb_rx = rte_eth_rx_burst(eth_port, 0, mbufs, BATCH_SIZE);
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for (i = 0; i < nb_rx; i++) {
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ev[i].flow_id = mbufs[i]->hash.rss;
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ev[i].op = RTE_EVENT_OP_NEW;
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ev[i].sched_type = RTE_SCHED_TYPE_ATOMIC;
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ev[i].queue_id = 0;
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ev[i].event_type = RTE_EVENT_TYPE_ETHDEV;
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ev[i].sub_event_type = 0;
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ev[i].priority = RTE_EVENT_DEV_PRIORITY_NORMAL;
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ev[i].mbuf = mbufs[i];
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}
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const int nb_tx = rte_event_enqueue_burst(dev_id, port_id, ev, nb_rx);
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if (nb_tx != nb_rx) {
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for(i = nb_tx; i < nb_rx; i++)
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rte_pktmbuf_free(mbufs[i]);
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}
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Forwarding of Events
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~~~~~~~~~~~~~~~~~~~~
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Now that the RX core has injected events, there is work to be done by the
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workers. Note that each worker will dequeue as many events as it can in a burst,
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process each one individually, and then burst the packets back into the
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eventdev.
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The worker can lookup the events source from ``event.queue_id``, which should
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indicate to the worker what workload needs to be performed on the event.
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Once done, the worker can update the ``event.queue_id`` to a new value, to send
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the event to the next stage in the pipeline.
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.. code-block:: c
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int timeout = 0;
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struct rte_event events[BATCH_SIZE];
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uint16_t nb_rx = rte_event_dequeue_burst(dev_id, worker_port_id, events, BATCH_SIZE, timeout);
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for (i = 0; i < nb_rx; i++) {
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/* process mbuf using events[i].queue_id as pipeline stage */
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struct rte_mbuf *mbuf = events[i].mbuf;
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/* Send event to next stage in pipeline */
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events[i].queue_id++;
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}
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uint16_t nb_tx = rte_event_enqueue_burst(dev_id, port_id, events, nb_rx);
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Egress of Events
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~~~~~~~~~~~~~~~~
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Finally, when the packet is ready for egress or needs to be dropped, we need
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to inform the eventdev that the packet is no longer being handled by the
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application. This can be done by calling dequeue() or dequeue_burst(), which
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indicates that the previous burst of packets is no longer in use by the
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application.
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An event driven worker thread has following typical workflow on fastpath:
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.. code-block:: c
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while (1) {
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rte_event_dequeue_burst(...);
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(event processing)
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rte_event_enqueue_burst(...);
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}
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Summary
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-------
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The eventdev library allows an application to easily schedule events as it
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requires, either using a run-to-completion or pipeline processing model. The
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queues and ports abstract the logical functionality of an eventdev, providing
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the application with a generic method to schedule events. With the flexible
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PMD infrastructure applications benefit of improvements in existing eventdevs
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and additions of new ones without modification.
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