5. Distributed Software Eventdev Poll Mode Driver

The distributed software event device is an eventdev driver which distributes the task of scheduling events among all the eventdev ports and the lcore threads using them.

5.1. Features

Queues

  • Atomic

  • Parallel

  • Single-Link

Ports

  • Load balanced (for Atomic, Ordered, Parallel queues)

  • Single Link (for single-link queues)

5.2. Configuration and Options

The distributed 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_dsw0") from the application

  • Use --vdev="event_dsw0" in the EAL options, which will call rte_vdev_init() internally

Example:

./your_eventdev_application --vdev="event_dsw0"

5.3. Limitations

5.3.1. Unattended Ports

The distributed software eventdev uses an internal signaling schema between the ports to achieve load balancing. In order for this to work, the application must perform enqueue and/or dequeue operations on all ports.

Producer-only ports which currently have no events to enqueue should periodically call rte_event_enqueue_burst() with a zero-sized burst.

Ports left unattended for longer periods of time will prevent load balancing, and also cause traffic interruptions on the flows which are in the process of being migrated.

5.3.2. Output Buffering

For efficiency reasons, the distributed software eventdev might not send enqueued events immediately to the destination port, but instead store them in an internal buffer in the source port.

In case no more events are enqueued on a port with buffered events, these events will be sent after the application has performed a number of enqueue and/or dequeue operations.

For explicit flushing, an application may call rte_event_enqueue_burst() with a zero-sized burst.

5.3.3. Priorities

The distributed software eventdev does not support event priorities.

5.3.4. Ordered Queues

The distributed software eventdev does not support the ordered queue type.

5.3.5. “All Types” Queues

The distributed software eventdev does not support queues of type RTE_EVENT_QUEUE_CFG_ALL_TYPES, which allow both atomic, ordered, and parallel events on the same queue.