doc: improve eventdev library guide

Add small amount of additional code, use consistent variable names
across code blocks, change the image to represent queues and
CPU cores intuitively. These help improve the eventdev library
documentation.

Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Gavin Hu <gavin.hu@arm.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Acked-by: Harry van Haaren <harry.van.haaren@intel.com>

doc/guides/prog_guide/eventdev.rst

@@ -1,5 +1,6 @@
 ..  SPDX-License-Identifier: BSD-3-Clause
     Copyright(c) 2017 Intel Corporation.
+    Copyright(c) 2018 Arm Limited.
 
 Event Device Library
 ====================
@@ -129,8 +130,10 @@ API Walk-through
 
 This section will introduce the reader to the eventdev API, showing how to
 create and configure an eventdev and use it for a two-stage atomic pipeline
-with a single core for TX. The diagram below shows the final state of the
-application after this walk-through:
+with one core each for RX and TX. RX and TX cores are shown here for
+illustration, refer to Eventdev Adapter documentation for further details.
+The diagram below shows the final state of the application after this
+walk-through:
 
 .. _figure_eventdev-usage1:
 
@@ -196,23 +199,29 @@ calling the setup function. Repeat this step for each queue, starting from
                 .nb_atomic_flows = 1024,
                 .nb_atomic_order_sequences = 1024,
         };
+        struct rte_event_queue_conf single_link_conf = {
+                .event_queue_cfg = RTE_EVENT_QUEUE_CFG_SINGLE_LINK,
+        };
         int dev_id = 0;
-        int queue_id = 0;
-        int err = rte_event_queue_setup(dev_id, queue_id, &atomic_conf);
+        int atomic_q_1 = 0;
+        int atomic_q_2 = 1;
+        int single_link_q = 2;
+        int err = rte_event_queue_setup(dev_id, atomic_q_1, &atomic_conf);
+        int err = rte_event_queue_setup(dev_id, atomic_q_2, &atomic_conf);
+        int err = rte_event_queue_setup(dev_id, single_link_q, &single_link_conf);
 
-The remainder of this walk-through assumes that the queues are configured as
-follows:
+As shown above, queue IDs are as follows:
 
  * id 0, atomic queue #1
  * id 1, atomic queue #2
  * id 2, single-link queue
 
+These queues are used for the remainder of this walk-through.
+
 Setting up Ports
 ~~~~~~~~~~~~~~~~
 
-Once queues are set up successfully, create the ports as required. Each port
-should be set up with its corresponding port_conf type, worker for worker cores,
-rx and tx for the RX and TX cores:
+Once queues are set up successfully, create the ports as required.
 
 .. code-block:: c
 
@@ -232,15 +241,24 @@ rx and tx for the RX and TX cores:
                 .new_event_threshold = 4096,
         };
         int dev_id = 0;
-        int port_id = 0;
-        int err = rte_event_port_setup(dev_id, port_id, &CORE_FUNCTION_conf);
+        int rx_port_id = 0;
+        int err = rte_event_port_setup(dev_id, rx_port_id, &rx_conf);
 
-It is now assumed that:
+        for(int worker_port_id = 1; worker_port_id <= 4; worker_port_id++) {
+	        int err = rte_event_port_setup(dev_id, worker_port_id, &worker_conf);
+        }
+
+        int tx_port_id = 5;
+	int err = rte_event_port_setup(dev_id, tx_port_id, &tx_conf);
+
+As shown above:
 
  * port 0: RX core
  * ports 1,2,3,4: Workers
  * port 5: TX core
 
+These ports are used for the remainder of this walk-through.
+
 Linking Queues and Ports
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -254,15 +272,14 @@ can be achieved like this:
 
 .. code-block:: c
 
-        uint8_t port_id = 0;
+        uint8_t rx_port_id = 0;
+        uint8_t tx_port_id = 5;
         uint8_t atomic_qs[] = {0, 1};
         uint8_t single_link_q = 2;
-        uint8_t tx_port_id = 5;
         uin8t_t priority = RTE_EVENT_DEV_PRIORITY_NORMAL;
 
-        for(int i = 0; i < 4; i++) {
-                int worker_port = i + 1;
-                int links_made = rte_event_port_link(dev_id, worker_port, atomic_qs, NULL, 2);
+        for(int worker_port_id = 1; worker_port_id <= 4; worker_port_id++) {
+                int links_made = rte_event_port_link(dev_id, worker_port_id, atomic_qs, NULL, 2);
         }
         int links_made = rte_event_port_link(dev_id, tx_port_id, &single_link_q, &priority, 1);
 
@@ -295,14 +312,14 @@ The following code shows how those packets can be enqueued into the eventdev:
                 ev[i].flow_id = mbufs[i]->hash.rss;
                 ev[i].op = RTE_EVENT_OP_NEW;
                 ev[i].sched_type = RTE_SCHED_TYPE_ATOMIC;
-                ev[i].queue_id = 0;
+                ev[i].queue_id = atomic_q_1;
                 ev[i].event_type = RTE_EVENT_TYPE_ETHDEV;
                 ev[i].sub_event_type = 0;
                 ev[i].priority = RTE_EVENT_DEV_PRIORITY_NORMAL;
                 ev[i].mbuf = mbufs[i];
         }
 
-        const int nb_tx = rte_event_enqueue_burst(dev_id, port_id, ev, nb_rx);
+        const int nb_tx = rte_event_enqueue_burst(dev_id, rx_port_id, ev, nb_rx);
         if (nb_tx != nb_rx) {
                 for(i = nb_tx; i < nb_rx; i++)
                         rte_pktmbuf_free(mbufs[i]);
@@ -334,7 +351,7 @@ the event to the next stage in the pipeline.
                 events[i].queue_id++;
         }
 
-        uint16_t nb_tx = rte_event_enqueue_burst(dev_id, port_id, events, nb_rx);
+        uint16_t nb_tx = rte_event_enqueue_burst(dev_id, worker_port_id, events, nb_rx);
 
 
 Egress of Events