Adding upstream version 18.2.2.upstream/18.2.2

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 132 insertions, 0 deletions

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+..  SPDX-License-Identifier: BSD-3-Clause
+    Copyright(c) 2017 Intel Corporation.
+
+Software Eventdev Poll Mode Driver
+==================================
+
+The software eventdev is an implementation of the eventdev API, that provides a
+wide range of the eventdev features. The eventdev relies on a CPU core to
+perform event scheduling. This PMD can use the service core library to run the
+scheduling function, allowing an application to utilize the power of service
+cores to multiplex other work on the same core if required.
+
+
+Features
+--------
+
+The software eventdev implements many features in the eventdev API;
+
+Queues
+ * Atomic
+ * Ordered
+ * Parallel
+ * Single-Link
+
+Ports
+ * Load balanced (for Atomic, Ordered, Parallel queues)
+ * Single Link (for single-link queues)
+
+Event Priorities
+ * Each event has a priority, which can be used to provide basic QoS
+
+
+Configuration and Options
+-------------------------
+
+The software eventdev is a vdev device, and as such can be created from the
+application code, or from the EAL command line:
+
+* Call ``rte_vdev_init("event_sw0")`` from the application
+
+* Use ``--vdev="event_sw0"`` in the EAL options, which will call
+  rte_vdev_init() internally
+
+Example:
+
+.. code-block:: console
+
+    ./your_eventdev_application --vdev="event_sw0"
+
+
+Scheduling Quanta
+~~~~~~~~~~~~~~~~~
+
+The scheduling quanta sets the number of events that the device attempts to
+schedule in a single schedule call performed by the service core. Note that
+is a *hint* only, and that fewer or more events may be scheduled in a given
+iteration.
+
+The scheduling quanta can be set using a string argument to the vdev
+create call:
+
+.. code-block:: console
+
+    --vdev="event_sw0,sched_quanta=64"
+
+
+Credit Quanta
+~~~~~~~~~~~~~
+
+The credit quanta is the number of credits that a port will fetch at a time from
+the instance's credit pool. Higher numbers will cause less overhead in the
+atomic credit fetch code, however it also reduces the overall number of credits
+in the system faster. A balanced number (e.g. 32) ensures that only small numbers
+of credits are pre-allocated at a time, while also mitigating performance impact
+of the atomics.
+
+Experimentation with higher values may provide minor performance improvements,
+at the cost of the whole system having less credits. On the other hand,
+reducing the quanta may cause measurable performance impact but provide the
+system with a higher number of credits at all times.
+
+A value of 32 seems a good balance however your specific application may
+benefit from a higher or reduced quanta size, experimentation is required to
+verify possible gains.
+
+.. code-block:: console
+
+    --vdev="event_sw0,credit_quanta=64"
+
+
+Limitations
+-----------
+
+The software eventdev implementation has a few limitations. The reason for
+these limitations is usually that the performance impact of supporting the
+feature would be significant.
+
+
+"All Types" Queues
+~~~~~~~~~~~~~~~~~~
+
+The software eventdev does not support creating queues that handle all types of
+traffic. An eventdev with this capability allows enqueuing Atomic, Ordered and
+Parallel traffic to the same queue, but scheduling each of them appropriately.
+
+The reason to not allow Atomic, Ordered and Parallel event types in the
+same queue is that it causes excessive branching in the code to enqueue packets
+to the queue, causing a significant performance impact.
+
+The ``RTE_EVENT_DEV_CAP_QUEUE_ALL_TYPES`` flag is not set in the
+``event_dev_cap`` field of the ``rte_event_dev_info`` struct for the software
+eventdev.
+
+Distributed Scheduler
+~~~~~~~~~~~~~~~~~~~~~
+
+The software eventdev is a centralized scheduler, requiring a service core to
+perform the required event distribution. This is not really a limitation but
+rather a design decision.
+
+The ``RTE_EVENT_DEV_CAP_DISTRIBUTED_SCHED`` flag is not set in the
+``event_dev_cap`` field of the ``rte_event_dev_info`` struct for the software
+eventdev.
+
+Dequeue Timeout
+~~~~~~~~~~~~~~~
+
+The eventdev API supports a timeout when dequeuing packets using the
+``rte_event_dequeue_burst`` function.
+This allows a core to wait for an event to arrive, or until ``timeout`` number
+of ticks have passed. Timeout ticks is not supported by the software eventdev
+for performance reasons.