1 .. SPDX-License-Identifier: BSD-3-Clause
2 Copyright 2018 The DPDK contributors
7 Environment or Architecture-specific Sources
8 --------------------------------------------
10 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.
11 As far as is possible, all such instances of architecture or env-specific code should be provided via standard APIs in the EAL.
13 By convention, a file is common if it is not located in a directory indicating that it is specific.
14 For instance, a file located in a subdir of "x86_64" directory is specific to this architecture.
15 A file located in a subdir of "linux" is specific to this execution environment.
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.
22 When absolutely necessary, there are several ways to handle specific code:
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:
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.
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.
44 Per Architecture Sources
45 ~~~~~~~~~~~~~~~~~~~~~~~~
47 The following config options can be used:
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.
52 Per Execution Environment Sources
53 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
55 The following config options can be used:
57 * ``CONFIG_RTE_EXEC_ENV`` is a string that contains the name of the executive environment.
58 * ``CONFIG_RTE_EXEC_ENV_FREEBSD`` or ``CONFIG_RTE_EXEC_ENV_LINUX`` are defined only if we are building for this execution environment.
66 This document describes the guidelines for DPDK library-level statistics counter
67 support. This includes guidelines for turning library statistics on and off and
68 requirements for preventing ABI changes when implementing statistics.
71 Mechanism to allow the application to turn library statistics on and off
72 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
74 Each library that maintains statistics counters should provide a single build
75 time flag that decides whether the statistics counter collection is enabled or
76 not. This flag should be exposed as a variable within the DPDK configuration
77 file. When this flag is set, all the counters supported by current library are
78 collected for all the instances of every object type provided by the library.
79 When this flag is cleared, none of the counters supported by the current library
80 are collected for any instance of any object type provided by the library:
82 .. code-block:: console
84 # DPDK file config/common_linux, config/common_freebsd, etc.
85 CONFIG_RTE_<LIBRARY_NAME>_STATS_COLLECT=y/n
87 The default value for this DPDK configuration file variable (either "yes" or
88 "no") is decided by each library.
91 Prevention of ABI changes due to library statistics support
92 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
94 The layout of data structures and prototype of functions that are part of the
95 library API should not be affected by whether the collection of statistics
96 counters is turned on or off for the current library. In practical terms, this
97 means that space should always be allocated in the API data structures for
98 statistics counters and the statistics related API functions are always built
99 into the code, regardless of whether the statistics counter collection is turned
100 on or off for the current library.
102 When the collection of statistics counters for the current library is turned
103 off, the counters retrieved through the statistics related API functions should
104 have a default value of zero.
107 Motivation to allow the application to turn library statistics on and off
108 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
110 It is highly recommended that each library provides statistics counters to allow
111 an application to monitor the library-level run-time events. Typical counters
112 are: number of packets received/dropped/transmitted, number of buffers
113 allocated/freed, number of occurrences for specific events, etc.
115 However, the resources consumed for library-level statistics counter collection
116 have to be spent out of the application budget and the counters collected by
117 some libraries might not be relevant to the current application. In order to
118 avoid any unwanted waste of resources and/or performance impacts, the
119 application should decide at build time whether the collection of library-level
120 statistics counters should be turned on or off for each library individually.
122 Library-level statistics counters can be relevant or not for specific
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
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.
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.
145 The statistics collection consumes a certain amount of CPU resources (cycles,
146 cache bandwidth, memory bandwidth, etc) that depends on:
148 * Number of libraries used by the current application that have statistics
149 counters collection turned on.
151 * Number of statistics counters maintained by each library per object type
152 instance (e.g. per port, table, pipeline, thread, etc).
154 * Number of instances created for each object type supported by each library.
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
165 PF and VF Considerations
166 ------------------------
168 The primary goal of DPDK is to provide a userspace dataplane. Managing VFs from
169 a PF driver is a control plane feature and developers should generally rely on
170 the Linux Kernel for that.
172 Developers should work with the Linux Kernel community to get the required
173 functionality upstream. PF functionality should only be added to DPDK for
174 testing and prototyping purposes while the kernel work is ongoing. It should
175 also be marked with an "EXPERIMENTAL" tag. If the functionality isn't
176 upstreamable then a case can be made to maintain the PF functionality in DPDK
177 without the EXPERIMENTAL tag.