1.. SPDX-License-Identifier: BSD-3-Clause 2 Copyright 2018 The DPDK contributors 3 4Design 5====== 6 7Environment or Architecture-specific Sources 8-------------------------------------------- 9 10In 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. 11As far as is possible, all such instances of architecture or env-specific code should be provided via standard APIs in the EAL. 12 13By convention, a file is common if it is not located in a directory indicating that it is specific. 14For instance, a file located in a subdir of "x86_64" directory is specific to this architecture. 15A file located in a subdir of "linuxapp" is specific to this execution environment. 16 17.. note:: 18 19 Code in DPDK libraries and applications should be generic. 20 The correct location for architecture or executive environment specific code is in the EAL. 21 22When absolutely necessary, there are several ways to handle specific code: 23 24* Use a ``#ifdef`` with the CONFIG option in the C code. 25 This can be done when the differences are small and they can be embedded in the same C file: 26 27 .. code-block:: c 28 29 #ifdef RTE_ARCH_I686 30 toto(); 31 #else 32 titi(); 33 #endif 34 35* Use the CONFIG option in the Makefile. This is done when the differences are more significant. 36 In this case, the code is split into two separate files that are architecture or environment specific. 37 This should only apply inside the EAL library. 38 39.. note:: 40 41 As in the linux kernel, the ``CONFIG_`` prefix is not used in C code. 42 This is only needed in Makefiles or shell scripts. 43 44Per Architecture Sources 45~~~~~~~~~~~~~~~~~~~~~~~~ 46 47The following config options can be used: 48 49* ``CONFIG_RTE_ARCH`` is a string that contains the name of the architecture. 50* ``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. 51 52Per Execution Environment Sources 53~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 54 55The following config options can be used: 56 57* ``CONFIG_RTE_EXEC_ENV`` is a string that contains the name of the executive environment. 58* ``CONFIG_RTE_EXEC_ENV_BSDAPP`` or ``CONFIG_RTE_EXEC_ENV_LINUXAPP`` are defined only if we are building for this execution environment. 59 60Library Statistics 61------------------ 62 63Description 64~~~~~~~~~~~ 65 66This document describes the guidelines for DPDK library-level statistics counter 67support. This includes guidelines for turning library statistics on and off and 68requirements for preventing ABI changes when implementing statistics. 69 70 71Mechanism to allow the application to turn library statistics on and off 72~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 73 74Each library that maintains statistics counters should provide a single build 75time flag that decides whether the statistics counter collection is enabled or 76not. This flag should be exposed as a variable within the DPDK configuration 77file. When this flag is set, all the counters supported by current library are 78collected for all the instances of every object type provided by the library. 79When this flag is cleared, none of the counters supported by the current library 80are collected for any instance of any object type provided by the library: 81 82.. code-block:: console 83 84 # DPDK file config/common_linuxapp, config/common_bsdapp, etc. 85 CONFIG_RTE_<LIBRARY_NAME>_STATS_COLLECT=y/n 86 87The default value for this DPDK configuration file variable (either "yes" or 88"no") is decided by each library. 89 90 91Prevention of ABI changes due to library statistics support 92~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 93 94The layout of data structures and prototype of functions that are part of the 95library API should not be affected by whether the collection of statistics 96counters is turned on or off for the current library. In practical terms, this 97means that space should always be allocated in the API data structures for 98statistics counters and the statistics related API functions are always built 99into the code, regardless of whether the statistics counter collection is turned 100on or off for the current library. 101 102When the collection of statistics counters for the current library is turned 103off, the counters retrieved through the statistics related API functions should 104have a default value of zero. 105 106 107Motivation to allow the application to turn library statistics on and off 108~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 109 110It is highly recommended that each library provides statistics counters to allow 111an application to monitor the library-level run-time events. Typical counters 112are: number of packets received/dropped/transmitted, number of buffers 113allocated/freed, number of occurrences for specific events, etc. 114 115However, the resources consumed for library-level statistics counter collection 116have to be spent out of the application budget and the counters collected by 117some libraries might not be relevant to the current application. In order to 118avoid any unwanted waste of resources and/or performance impacts, the 119application should decide at build time whether the collection of library-level 120statistics counters should be turned on or off for each library individually. 121 122Library-level statistics counters can be relevant or not for specific 123applications: 124 125* For Application A, counters maintained by Library X are always relevant and 126 the application needs to use them to implement certain features, such as traffic 127 accounting, logging, application-level statistics, etc. In this case, 128 the application requires that collection of statistics counters for Library X is 129 always turned on. 130 131* For Application B, counters maintained by Library X are only useful during the 132 application debug stage and are not relevant once debug phase is over. In this 133 case, the application may decide to turn on the collection of Library X 134 statistics counters during the debug phase and at a later stage turn them off. 135 136* For Application C, counters maintained by Library X are not relevant at all. 137 It might be that the application maintains its own set of statistics counters 138 that monitor a different set of run-time events (e.g. number of connection 139 requests, number of active users, etc). It might also be that the application 140 uses multiple libraries (Library X, Library Y, etc) and it is interested in the 141 statistics counters of Library Y, but not in those of Library X. In this case, 142 the application may decide to turn the collection of statistics counters off for 143 Library X and on for Library Y. 144 145The statistics collection consumes a certain amount of CPU resources (cycles, 146cache bandwidth, memory bandwidth, etc) that depends on: 147 148* Number of libraries used by the current application that have statistics 149 counters collection turned on. 150 151* Number of statistics counters maintained by each library per object type 152 instance (e.g. per port, table, pipeline, thread, etc). 153 154* Number of instances created for each object type supported by each library. 155 156* Complexity of the statistics logic collection for each counter: when only 157 some occurrences of a specific event are valid, additional logic is typically 158 needed to decide whether the current occurrence of the event should be counted 159 or not. For example, in the event of packet reception, when only TCP packets 160 with destination port within a certain range should be recorded, conditional 161 branches are usually required. When processing a burst of packets that have been 162 validated for header integrity, counting the number of bits set in a bitmask 163 might be needed. 164 165PF and VF Considerations 166------------------------ 167 168The primary goal of DPDK is to provide a userspace dataplane. Managing VFs from 169a PF driver is a control plane feature and developers should generally rely on 170the Linux Kernel for that. 171 172Developers should work with the Linux Kernel community to get the required 173functionality upstream. PF functionality should only be added to DPDK for 174testing and prototyping purposes while the kernel work is ongoing. It should 175also be marked with an "EXPERIMENTAL" tag. If the functionality isn't 176upstreamable then a case can be made to maintain the PF functionality in DPDK 177without the EXPERIMENTAL tag. 178