--- /dev/null
+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.
+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.
+
+.. note::
+
+ Code in DPDK libraries and applications should be generic.
+ The correct location for architecture or executive environment specific code is in the EAL.
+
+When absolutely necessary, there are several ways to handle specific code:
+
+* Use a ``#ifdef`` with the CONFIG option in the C code.
+ This can be done when the differences are small and they can be embedded in the same C file:
+
+ .. code-block:: c
+
+ #ifdef RTE_ARCH_I686
+ toto();
+ #else
+ titi();
+ #endif
+
+* Use the CONFIG option in the Makefile. This is done when the differences are more significant.
+ In this case, the code is split into two separate files that are architecture or environment specific.
+ This should only apply inside the EAL library.
+
+.. note::
+
+ As in the linux kernel, the ``CONFIG_`` prefix is not used in C code.
+ This is only needed in Makefiles or shell scripts.
+
+Per Architecture Sources
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+The following config options can be used:
+
+* ``CONFIG_RTE_ARCH`` is a string that contains the name of the architecture.
+* ``CONFIG_RTE_ARCH_I686``, ``CONFIG_RTE_ARCH_X86_64``, ``CONFIG_RTE_ARCH_X86_64_32`` or ``CONFIG_RTE_ARCH_PPC_64`` are defined only if we are building for those architectures.
+
+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.
+
+Library Statistics
+------------------
+
+Description
+~~~~~~~~~~~
+
+This document describes the guidelines for DPDK library-level statistics counter
+support. This includes guidelines for turning library statistics on and off and
+requirements for preventing ABI changes when implementing statistics.
+
+
+Mechanism to allow the application to turn library statistics on and off
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Each library that maintains statistics counters should provide a single build
+time flag that decides whether the statistics counter collection is enabled or
+not. This flag should be exposed as a variable within the DPDK configuration
+file. When this flag is set, all the counters supported by current library are
+collected for all the instances of every object type provided by the library.
+When this flag is cleared, none of the counters supported by the current library
+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.
+ CONFIG_RTE_<LIBRARY_NAME>_STATS_COLLECT=y/n
+
+The default value for this DPDK configuration file variable (either "yes" or
+"no") is decided by each library.
+
+
+Prevention of ABI changes due to library statistics support
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The layout of data structures and prototype of functions that are part of the
+library API should not be affected by whether the collection of statistics
+counters is turned on or off for the current library. In practical terms, this
+means that space should always be allocated in the API data structures for
+statistics counters and the statistics related API functions are always built
+into the code, regardless of whether the statistics counter collection is turned
+on or off for the current library.
+
+When the collection of statistics counters for the current library is turned
+off, the counters retrieved through the statistics related API functions should
+have a default value of zero.
+
+
+Motivation to allow the application to turn library statistics on and off
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+It is highly recommended that each library provides statistics counters to allow
+an application to monitor the library-level run-time events. Typical counters
+are: number of packets received/dropped/transmitted, number of buffers
+allocated/freed, number of occurrences for specific events, etc.
+
+However, the resources consumed for library-level statistics counter collection
+have to be spent out of the application budget and the counters collected by
+some libraries might not be relevant to the current application. In order to
+avoid any unwanted waste of resources and/or performance impacts, the
+application should decide at build time whether the collection of library-level
+statistics counters should be turned on or off for each library individually.
+
+Library-level statistics counters can be relevant or not for specific
+applications:
+
+* For Application A, counters maintained by Library X are always relevant and
+ the application needs to use them to implement certain features, such as traffic
+ accounting, logging, application-level statistics, etc. In this case,
+ the application requires that collection of statistics counters for Library X is
+ always turned on.
+
+* For Application B, counters maintained by Library X are only useful during the
+ application debug stage and are not relevant once debug phase is over. In this
+ case, the application may decide to turn on the collection of Library X
+ statistics counters during the debug phase and at a later stage turn them off.
+
+* For Application C, counters maintained by Library X are not relevant at all.
+ It might be that the application maintains its own set of statistics counters
+ that monitor a different set of run-time events (e.g. number of connection
+ requests, number of active users, etc). It might also be that the application
+ uses multiple libraries (Library X, Library Y, etc) and it is interested in the
+ statistics counters of Library Y, but not in those of Library X. In this case,
+ the application may decide to turn the collection of statistics counters off for
+ Library X and on for Library Y.
+
+The statistics collection consumes a certain amount of CPU resources (cycles,
+cache bandwidth, memory bandwidth, etc) that depends on:
+
+* Number of libraries used by the current application that have statistics
+ counters collection turned on.
+
+* Number of statistics counters maintained by each library per object type
+ instance (e.g. per port, table, pipeline, thread, etc).
+
+* Number of instances created for each object type supported by each library.
+
+* Complexity of the statistics logic collection for each counter: when only
+ some occurrences of a specific event are valid, additional logic is typically
+ needed to decide whether the current occurrence of the event should be counted
+ or not. For example, in the event of packet reception, when only TCP packets
+ with destination port within a certain range should be recorded, conditional
+ branches are usually required. When processing a burst of packets that have been
+ validated for header integrity, counting the number of bits set in a bitmask
+ might be needed.
Code Review / deb_dpdk.git / blobdiff