docs: better docs, mv doxygen to sphinx

This patch refactors the VPP sphinx docs
in order to make it easier to consume
for external readers as well as VPP developers.

It also makes sphinx the single source
of documentation, which simplifies maintenance
and operation.

Most important updates are:

- reformat the existing documentation as rst
- split RELEASE.md and move it into separate rst files
- remove section 'events'
- remove section 'archive'
- remove section 'related projects'
- remove section 'feature by release'
- remove section 'Various links'
- make (Configuration reference, CLI docs,
  developer docs) top level items in the list
- move 'Use Cases' as part of 'About VPP'
- move 'Troubleshooting' as part of 'Getting Started'
- move test framework docs into 'Developer Documentation'
- add a 'Contributing' section for gerrit,
  docs and other contributer related infos
- deprecate doxygen and test-docs targets
- redirect the "make doxygen" target to "make docs"

Type: refactor

Change-Id: I552a5645d5b7964d547f99b1336e2ac24e7c209f
Signed-off-by: Nathan Skrzypczak <nathan.skrzypczak@gmail.com>
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>

1 files changed, 87 insertions, 0 deletions

diff --git a/docs/developer/corearchitecture/multiarch/arbfns.rst b/docs/developer/corearchitecture/multiarch/arbfns.rst
new file mode 100644
index 00000000000..d469bd8a140
--- /dev/null
+++ b/docs/developer/corearchitecture/multiarch/arbfns.rst
@@ -0,0 +1,87 @@
+Multi-Architecture Arbitrary Function Cookbook
+==============================================
+
+Optimizing arbitrary functions for multiple architectures is simple
+enough, and very similar to process used to produce multi-architecture
+graph node dispatch functions.
+
+As with multi-architecture graph nodes, we compile source files
+multiple times, generating multiple implementations of the original
+function, and a public selector function.
+
+Details
+-------
+
+Decorate function definitions with CLIB_MARCH_FN macros. For example:
+
+Change the original function prototype...
+
+::
+
+   u32 vlib_frame_alloc_to_node (vlib_main_t * vm, u32 to_node_index,
+                                 u32 frame_flags)
+
+...by recasting the function name and return type as the first two
+arguments to the CLIB_MARCH_FN macro:
+
+::
+
+    CLIB_MARCH_FN (vlib_frame_alloc_to_node, u32, vlib_main_t * vm,
+                   u32 to_node_index, u32 frame_flags)
+
+In the actual vpp image, several versions of vlib_frame_alloc_to_node
+will appear: vlib_frame_alloc_to_node_avx2,
+vlib_frame_alloc_to_node_avx512, and so forth.
+
+
+For each multi-architecture function, use the CLIB_MARCH_FN_SELECT
+macro to help generate the one-and-only multi-architecture selector
+function:
+
+::
+
+    #ifndef CLIB_MARCH_VARIANT
+    u32
+    vlib_frame_alloc_to_node (vlib_main_t * vm, u32 to_node_index,
+    			  u32 frame_flags)
+    {
+      return CLIB_MARCH_FN_SELECT (vlib_frame_alloc_to_node)
+        (vm, to_node_index, frame_flags);
+    }
+    #endif /* CLIB_MARCH_VARIANT */
+
+Once bound, the multi-architecture selector function is about as
+expensive as an indirect function call; which is to say: not very
+expensive.
+
+Modify CMakeLists.txt
+---------------------
+
+If the component in question already lists "MULTIARCH_SOURCES", simply
+add the indicated .c file to the list.  Otherwise, add as shown
+below. Note that the added file "new_multiarch_node.c" should appear in
+*both* SOURCES and MULTIARCH_SOURCES:
+
+::
+
+    add_vpp_plugin(myplugin
+      SOURCES
+      multiarch_code.c
+      ...
+
+      MULTIARCH_SOURCES
+      multiarch_code.c
+      ...
+     )
+
+A Word to the Wise
+------------------
+
+A file which liberally mixes functions worth compiling for multiple
+architectures and functions which are not will end up full of
+#ifndef CLIB_MARCH_VARIANT conditionals. This won't do a thing to make
+the code look any better.
+
+Depending on requirements, it may make sense to move functions to
+(new) files to reduce complexity and/or improve legibility of the
+resulting code.