6. 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.

6.1. Features

Queues

  • Atomic

  • Parallel

  • Single-Link

Ports

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

  • Single Link (for single-link queues)

6.2. 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"

6.3. Limitations

6.3.1. Port Maintenance

The distributed software eventdev uses an internal signaling scheme between the ports to achieve load balancing. Therefore, it does not set the RTE_EVENT_DEV_CAP_MAINTENANCE_FREE flag.

During periods when the application thread using a particular port is neither attempting to enqueue nor to dequeue events, it must repeatedly call rte_event_maintain() on that port.

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

6.3.2. 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.

To immediately flush a port’s output buffer, an application may call rte_event_maintain() with op set to RTE_EVENT_DEV_MAINT_OP_FLUSH.

Repeated calls to rte_event_maintain() will also flush the output buffers.

6.3.3. Priorities

The distributed software eventdev does not support event priorities.

6.3.4. Ordered Queues

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

6.3.5. “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.