doc: describe optimizations using C11 atomic builtins

[dpdk.git] / doc / guides / contributing / design.rst

diff --git a/doc/guides/contributing/design.rst b/doc/guides/contributing/design.rst
index 651fd22..5fe7f63 100644 (file)
--- a/doc/guides/contributing/design.rst
+++ b/doc/guides/contributing/design.rst
@@ -7,12 +7,12 @@ Design
 Environment or Architecture-specific Sources
 --------------------------------------------
 
-In DPDK and DPDK applications, some code is specific to an architecture (i686, x86_64) or to an executive environment (bsdapp or linuxapp) and so on.
+In DPDK and DPDK applications, some code is specific to an architecture (i686, x86_64) or to an executive environment (freebsd or linux) and so on.
 As far as is possible, all such instances of architecture or env-specific code should be provided via standard APIs in the EAL.
 
 By convention, a file is common if it is not located in a directory indicating that it is specific.
 For instance, a file located in a subdir of "x86_64" directory is specific to this architecture.
-A file located in a subdir of "linuxapp" is specific to this execution environment.
+A file located in a subdir of "linux" is specific to this execution environment.
 
 .. note::
 
@@ -55,7 +55,23 @@ Per Execution Environment Sources
 The following config options can be used:
 
 * ``CONFIG_RTE_EXEC_ENV`` is a string that contains the name of the executive environment.
-* ``CONFIG_RTE_EXEC_ENV_BSDAPP`` or ``CONFIG_RTE_EXEC_ENV_LINUXAPP`` are defined only if we are building for this execution environment.
+* ``CONFIG_RTE_EXEC_ENV_FREEBSD`` or ``CONFIG_RTE_EXEC_ENV_LINUX`` are defined only if we are building for this execution environment.
+
+Mbuf features
+-------------
+
+The ``rte_mbuf`` structure must be kept small (128 bytes).
+
+In order to add new features without wasting buffer space for unused features,
+some fields and flags can be registered dynamically in a shared area.
+The "dynamic" mbuf area is the default choice for the new features.
+
+The "dynamic" area is eating the remaining space in mbuf,
+and some existing "static" fields may need to become "dynamic".
+
+Adding a new static field or flag must be an exception matching many criteria
+like (non exhaustive): wide usage, performance, size.
+
 
 Library Statistics
 ------------------
@@ -81,7 +97,7 @@ are collected for any instance of any object type provided by the library:
 
 .. code-block:: console
 
-   # DPDK file config/common_linuxapp, config/common_bsdapp, etc.
+   # DPDK file config/common_linux, config/common_freebsd, etc.
    CONFIG_RTE_<LIBRARY_NAME>_STATS_COLLECT=y/n
 
 The default value for this DPDK configuration file variable (either "yes" or