41. Event Ethernet Tx Adapter Library

The DPDK Eventdev API allows the application to use an event driven programming model for packet processing in which the event device distributes events referencing packets to the application cores in a dynamic load balanced fashion while handling atomicity and packet ordering. Event adapters provide the interface between the ethernet, crypto and timer devices and the event device. Event adapter APIs enable common application code by abstracting PMD specific capabilities. The Event ethernet Tx adapter provides configuration and data path APIs for the transmit stage of the application allowing the same application code to use eventdev PMD support or in its absence, a common implementation.

In the common implementation, the application enqueues mbufs to the adapter which runs as a rte_service function. The service function dequeues events from its event port and transmits the mbufs referenced by these events.

41.1. API Walk-through

This section will introduce the reader to the adapter API. The application has to first instantiate an adapter which is associated with a single eventdev, next the adapter instance is configured with Tx queues, finally the adapter is started and the application can start enqueuing mbufs to it.

41.1.1. Creating an Adapter Instance

An adapter instance is created using rte_event_eth_tx_adapter_create(). This function is passed the event device to be associated with the adapter and port configuration for the adapter to setup an event port if the adapter needs to use a service function.

If the application desires to have finer control of eventdev port configuration, it can use the rte_event_eth_tx_adapter_create_ext() function. The rte_event_eth_tx_adapter_create_ext() function is passed a callback function. The callback function is invoked if the adapter needs to use a service function and needs to create an event port for it. The callback is expected to fill the struct rte_event_eth_tx_adapter_conf structure passed to it.

struct rte_event_dev_info dev_info;
struct rte_event_port_conf tx_p_conf = {0};

err = rte_event_dev_info_get(id, &dev_info);

tx_p_conf.new_event_threshold = dev_info.max_num_events;
tx_p_conf.dequeue_depth = dev_info.max_event_port_dequeue_depth;
tx_p_conf.enqueue_depth = dev_info.max_event_port_enqueue_depth;

err = rte_event_eth_tx_adapter_create(id, dev_id, &tx_p_conf);

41.1.2. Adding Tx Queues to the Adapter Instance

Ethdev Tx queues are added to the instance using the rte_event_eth_tx_adapter_queue_add() function. A queue value of -1 is used to indicate all queues within a device.

int err = rte_event_eth_tx_adapter_queue_add(id,
                                             eth_dev_id,
                                             q);

41.1.3. Querying Adapter Capabilities

The rte_event_eth_tx_adapter_caps_get() function allows the application to query the adapter capabilities for an eventdev and ethdev combination. Currently, the only capability flag defined is RTE_EVENT_ETH_TX_ADAPTER_CAP_INTERNAL_PORT, the application can query this flag to determine if a service function is associated with the adapter and retrieve its service identifier using the rte_event_eth_tx_adapter_service_id_get() API.

int err = rte_event_eth_tx_adapter_caps_get(dev_id, eth_dev_id, &cap);

if (!(cap & RTE_EVENT_ETH_TX_ADAPTER_CAP_INTERNAL_PORT))
        err = rte_event_eth_tx_adapter_service_id_get(id, &service_id);

41.1.4. Linking a Queue to the Adapter’s Event Port

If the adapter uses a service function as described in the previous section, the application is required to link a queue to the adapter’s event port. The adapter’s event port can be obtained using the rte_event_eth_tx_adapter_event_port_get() function. The queue can be configured with the RTE_EVENT_QUEUE_CFG_SINGLE_LINK since it is linked to a single event port.

41.1.5. Configuring the Service Function

If the adapter uses a service function, the application can assign a service core to the service function as shown below.

if (rte_event_eth_tx_adapter_service_id_get(id, &service_id) == 0)
        rte_service_map_lcore_set(service_id, TX_CORE_ID);

41.1.6. Starting the Adapter Instance

The application calls rte_event_eth_tx_adapter_start() to start the adapter. This function calls the start callback of the eventdev PMD if supported, and the rte_service_run_state_set() to enable the service function if one exists.

41.1.7. Enqueuing Packets to the Adapter

The application needs to notify the adapter about the transmit port and queue used to send the packet. The transmit port is set in the struct rte mbuf::port field and the transmit queue is set using the rte_event_eth_tx_adapter_txq_set() function.

If the eventdev PMD supports the RTE_EVENT_ETH_TX_ADAPTER_CAP_INTERNAL_PORT capability for a given ethernet device, the application should use the rte_event_eth_tx_adapter_enqueue() function to enqueue packets to the adapter.

If the adapter uses a service function for the ethernet device then the application should use the rte_event_enqueue_burst() function.

struct rte_event event;

if (cap & RTE_EVENT_ETH_TX_ADAPTER_CAP_INTERNAL_PORT) {

        event.mbuf = m;
        eq_flags = 0;

        m->port = tx_port;
        rte_event_eth_tx_adapter_txq_set(m, tx_queue_id);

        rte_event_eth_tx_adapter_enqueue(dev_id, ev_port, &event, 1, eq_flags);
} else {

        event.queue_id = qid; /* event queue linked to adapter port */
        event.op = RTE_EVENT_OP_NEW;
        event.event_type = RTE_EVENT_TYPE_CPU;
        event.sched_type = RTE_SCHED_TYPE_ATOMIC;
        event.mbuf = m;

        m->port = tx_port;
        rte_event_eth_tx_adapter_txq_set(m, tx_queue_id);

        rte_event_enqueue_burst(dev_id, ev_port, &event, 1);
}

41.1.8. Getting Adapter Statistics

The rte_event_eth_tx_adapter_stats_get() function reports counters defined in struct rte_event_eth_tx_adapter_stats. The counter values are the sum of the counts from the eventdev PMD callback if the callback is supported, and the counts maintained by the service function, if one exists.