[PATCH 2/2] doc/contributing: guidelines for logging, tracing and telemetry

[Bruce Richardson <bruce.richardson@intel.com>]

As discussed by DPDK technical board [1], out contributor guide should
include some details as to when to use logging vs tracing vs telemetry
to provide the end user with information about the running process and
the DPDK libraries it uses.

[1] https://mails.dpdk.org/archives/dev/2023-March/265204.html

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
---
 doc/guides/contributing/coding_style.rst |  2 ++
 doc/guides/contributing/design.rst       | 34 ++++++++++++++++++++++++
 doc/guides/prog_guide/telemetry_lib.rst  |  2 ++
 doc/guides/prog_guide/trace_lib.rst      |  2 ++
 4 files changed, 40 insertions(+)

diff --git a/doc/guides/contributing/coding_style.rst b/doc/guides/contributing/coding_style.rst
index f50a78a346..13b2390d9e 100644
--- a/doc/guides/contributing/coding_style.rst
+++ b/doc/guides/contributing/coding_style.rst
@@ -794,6 +794,8 @@ Control Statements
                  /* NOTREACHED */
          }
 
+.. _dynamic_logging:
+
 Dynamic Logging
 ---------------
 
diff --git a/doc/guides/contributing/design.rst b/doc/guides/contributing/design.rst
index d24a7ff6a0..9edf3ea43b 100644
--- a/doc/guides/contributing/design.rst
+++ b/doc/guides/contributing/design.rst
@@ -4,6 +4,40 @@
 Design
 ======
 
+Runtime Information - Logging, Tracing and Telemetry
+-------------------------------------------------------
+
+It is often desirable to provide information to the end-user as to what is happening to the application at runtime.
+DPDK provides a number of built-in mechanisms to provide this introspection:
+
+* :ref:`Logging<dynamic_logging>`
+* :ref:`Tracing<trace_library>`
+* :ref:`Telemetry<telemetry_library>`
+
+Each of these has it's own strengths and suitabilities for use within DPDK components.
+
+Below are some guidelines for when each should be used:
+
+* For reporting error conditions, or other abnormal runtime issues, *logging* should be used.
+  Depending on the severity of the issue, the appropriate log level, for example,
+  ``ERROR``, ``WARNING`` or ``NOTICE``, should be used.
+* In general, it is not recommended that the DPDK logging functions should be used for debugging.
+  Although the ``DEBUG`` log level may be used in components, it should only be used sparingly,
+  and the *tracing* functionality used instead.
+  More specifically:
+
+  * for cases where a path through the code is only likely to be taken once,
+    for example, initialization code, either *logging* at ``DEBUG`` level or *tracing* may be used -
+    though tracing is preferred.
+  * where a path is to be taken multiple times within a short timeframe, for example,
+    datapath or regular control plane code, *tracing* should be used.
+
+* For numerical or statistical data generated by a component, for example, per-packet statistics,
+  *telemetry* should be used.
+* For any data where the data may need to be gathered at any point in the execution to help assess the state of the application component,
+  for example, core configuration, device information, *telemetry* should be used.
+
+
 Environment or Architecture-specific Sources
 --------------------------------------------
 
diff --git a/doc/guides/prog_guide/telemetry_lib.rst b/doc/guides/prog_guide/telemetry_lib.rst
index 32f525a67f..71f8bd735e 100644
--- a/doc/guides/prog_guide/telemetry_lib.rst
+++ b/doc/guides/prog_guide/telemetry_lib.rst
@@ -1,6 +1,8 @@
 ..  SPDX-License-Identifier: BSD-3-Clause
     Copyright(c) 2020 Intel Corporation.
 
+.. _telemetry_library:
+
 Telemetry Library
 =================
 
diff --git a/doc/guides/prog_guide/trace_lib.rst b/doc/guides/prog_guide/trace_lib.rst
index e5718feddc..a3b8a7c2eb 100644
--- a/doc/guides/prog_guide/trace_lib.rst
+++ b/doc/guides/prog_guide/trace_lib.rst
@@ -1,6 +1,8 @@
 ..  SPDX-License-Identifier: BSD-3-Clause
     Copyright(C) 2020 Marvell International Ltd.
 
+.. _trace_library:
+
 Trace Library
 =============
 
-- 
2.39.2