doc: add telemetry how-to

This patch adds all documentation for telemetry.

A description on how to use the Telemetry API with a DPDK
application is given in this document.

It also adds a release notes update for telemetry.

Signed-off-by: Ciara Power <ciara.power@intel.com>
Signed-off-by: Brian Archbold <brian.archbold@intel.com>
Signed-off-by: Kevin Laatz <kevin.laatz@intel.com>
Acked-by: Harry van Haaren <harry.van.haaren@intel.com>
Acked-by: Marko Kovacevic <marko.kovacevic@intel.com>

MAINTAINERS

@@ -1205,6 +1205,7 @@ Telemetry - EXPERIMENTAL
 M: Kevin Laatz <kevin.laatz@intel.com>
 F: lib/librte_telemetry/
 F: usertools/dpdk-telemetry-client.py
+F: doc/guides/howto/telemetry.rst
 
 BPF - EXPERIMENTAL
 M: Konstantin Ananyev <konstantin.ananyev@intel.com>

doc/guides/howto/index.rst

@@ -17,3 +17,4 @@ HowTo Guides
     virtio_user_for_container_networking
     virtio_user_as_exceptional_path
     packet_capture_framework
+    telemetry

doc/guides/howto/telemetry.rst

@@ -0,0 +1,85 @@
+..  SPDX-License-Identifier: BSD-3-Clause
+    Copyright(c) 2018 Intel Corporation.
+
+DPDK Telemetry API User Guide
+==============================
+
+This document describes how the Data Plane Development Kit(DPDK) Telemetry API
+is used for querying port statistics from incoming traffic.
+
+Introduction
+------------
+
+The ``librte_telemetry`` provides the functionality so that users may query
+metrics from incoming port traffic. The application which initializes packet
+forwarding will act as the server, sending metrics to the requesting application
+which acts as the client.
+
+In DPDK, applications are used to initialize the ``telemetry``. To view incoming
+traffic on featured ports, the application should be run first (ie. after ports
+are configured). Once the application is running, the service assurance agent
+(for example the collectd plugin) should be run to begin querying the API.
+
+A client connects their Service Assurance application to the DPDK application
+via a UNIX socket. Once a connection is established, a client can send JSON
+messages to the DPDK application requesting metrics via another UNIX client.
+This request is then handled and parsed if valid. The response is then
+formatted in JSON and sent back to the requesting client.
+
+Pre-requisites
+~~~~~~~~~~~~~~
+
+* Python ≥ 2.5
+
+* Jansson library for JSON serialization
+
+Test Environment
+----------------
+
+``telemetry`` offers a range of selftests that a client can run within
+the DPDK application.
+
+Selftests are disabled by default. They can be enabled by setting the 'selftest'
+variable to 1 in rte_telemetry_initial_accept().
+
+Note: this 'hardcoded' value is temporary.
+
+Configuration
+-------------
+
+Enable the telemetry API by modifying the following config option before
+building DPDK::
+
+        CONFIG_RTE_LIBRTE_TELEMETRY=y
+
+Note: Meson will pick this up automatically if ``libjansson`` is available.
+
+Running the Application
+-----------------------
+
+The following steps demonstrate how to run the ``telemetry`` API  to query all
+statistics on all active ports, using the ``telemetry_client`` python script
+to query.
+Note: This guide assumes packet generation is applicable and the user is
+testing with testpmd as a DPDK primary application to forward packets, although
+any DPDK application is applicable.
+
+#. Launch testpmd as the primary application with ``telemetry``.::
+
+        ./app/testpmd --telemetry
+
+#. Launch the ``telemetry`` python script with a client filepath.::
+
+        python usertools/telemetry_client.py /var/run/some_client
+
+   The client filepath is going to be used to setup our UNIX connection with the
+   DPDK primary application, in this case ``testpmd``
+   This will initialize a menu where a client can proceed to recursively query
+   statistics, request statistics once or unregister the file_path, thus exiting
+   the menu.
+
+#. Send traffic to any or all available ports from a traffic generator.
+   Select a query option(recursive or singular polling).
+   The metrics will then be displayed on the client terminal in JSON format.
+
+#. Once finished, unregister the client using the menu command.

doc/guides/rel_notes/release_18_11.rst

@@ -254,6 +254,12 @@ New Features
   to containers and host applications that need to have their cores frequency
   controlled based on the rules contained in the policy.
 
+* **Added Telemetry API.**
+
+  Added the telemetry API which allows applications to transparently expose
+  their telemetry via a UNIX socket in JSON. The JSON can be consumed by any
+  Service Assurance agent, such as CollectD.
+
 * **Added ability to switch queue deferred start flag on testpmd app.**
 
   Added a console command to testpmd app, giving ability to switch