Re: [dpdk-dev] [RFC] eventdev: event tx adapter APIs

["Rao, Nikhil" <nikhil.rao@intel.com>]

On 6/4/2018 10:41 AM, Jerin Jacob wrote:
> -----Original Message-----
>> Date: Fri, 1 Jun 2018 23:47:00 +0530
>> From: "Rao, Nikhil" <nikhil.rao@intel.com>
>> To: Jerin Jacob <jerin.jacob@caviumnetworks.com>
>> CC: hemant.agrawal@nxp.com, dev@dpdk.org, narender.vangati@intel.com,
>>   abhinandan.gujjar@intel.com, gage.eads@intel.com, nikhil.rao@intel.com
>> Subject: Re: [RFC] eventdev: event tx adapter APIs
>> User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101
>>   Thunderbird/52.8.0
>>
>>
>> Hi Jerin,
> 
>
>> The workers invoke rte_event_enqueue_burst() to their local port not to the
>> extra port as you described. The queue ID specified when
>> enqueuing is linked to the the adapter's port, the adapter reads these
>> events and transmits mbufs on the
>> ethernet port and queue specified in these mbufs. The diagram below
>> illustrates what I just described.
>>
>> +------+
>> |      |   +----+
>> |Worker+-->+port+--+
>> |      |   +----+  |                                         +----+
>> +------+           |                                     +-->+eth0|
>>                     |  +---------+            +-------+   |   +----+
>>                     +--+         |   +----+   |       +---+   +----+
>>                        |  Queue  +-->+port+-->+Adapter|------>+eth1|
>>                     +--+         |   +----+   |       +---+   +----+
>> +------+           |  +---------+            +-------+   |   +----+
>> |      |   +----+  |                                     +-->+eth2|
>> |Worker+-->+port+--+                                         +----+
>> |      |   +----+
>> +------+
> 
> 
> Makes sense. One suggestion here, Since we have ALL type queue and
> normal queues, Can we move the queue change or sched_type change code
> from the application and move that down to function pointer abstraction(any
> way adapter knows which queues to enqueue for), that way we can have same
> final stage code for ALL type queues and Normal queues.
> 
Yes, I see the queue/sched type change approach followed in 
pipeline_worker_tx.c, a queue id can be provided in 
rte_event_eth_tx_adapter_conf

+struct rte_event_eth_tx_adapter_conf {
+	uint8_t event_port_id;
+	/**< Event port identifier, the adapter dequeues mbuf events from this
+	 * port.
+	 */
+	uint16_t tx_metadata_off;
+	/**<  Offset of struct rte_event_eth_tx_adapter_meta in the private
+	 * area of the mbuf
+	 */
+	uint32_t max_nb_tx;
+	/**< The adapter can return early if it has processed at least
+	 * max_nb_tx mbufs. This isn't treated as a requirement; batching may
+	 * cause the adapter to process more than max_nb_tx mbufs.
+	 */
+};

</sniped>

>> The worker core will receive events pointing to mbufs that need to be
>> transmitted to different
>> ports/queues, as described above. The port and the queue will be populated
>> in the mbuf and the
>> API can be as below
>>
>> uint16_t rte_event_eth_tx_adapter_enqueue(uint8_t instance_id, uint8_t event_port_id, const struct rte_event ev[], uint16_t nb_events);
>>
>> Let me know if that works for you.
> 
> Yes. That API works for me. I think, we can leverage "struct
> rte_eventdev" area for adding new function pointer. Just like
> enqueue_new_burst, enqueue_forward_burst variants, we can add one more
> there, so that we can reuse that hot cacheline for all fastpath function pointer case.
> That would translate to adding "uint8_t dev_id" on the above API.
The dev_id can be derived from the instance_id, does that work ?

I need some clarification on the configuration API/flow. The 
eventdev_pipeline sample app checks if DEV_TX_OFFLOAD_MT_LOCKFREE flag 
is set on all ethernet devices and if so, uses the pipeline_worker_tx 
path as opposed to the "consumer" function, if we were to use the 
adapter to replace some of the sample code then it seems like the 
RTE_EVENT_ETH_TX_ADAPTER_CAP_INTERNAL_PORT is hardware assist for the 
pipeline worker tx mode, the adapter would support 2 modes (consumer and 
worker_tx, borrowing terminology from the sample), worker_tx would only 
be supported if the eventdev supports 
RTE_EVENT_ETH_TX_ADAPTER_CAP_INTERNAL_PORT (at least in the first version)

Thanks,
Nikhil