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7c673cae FG |
1 | Design |
2 | ====== | |
3 | ||
4 | Environment or Architecture-specific Sources | |
5 | -------------------------------------------- | |
6 | ||
7 | 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. | |
8 | As far as is possible, all such instances of architecture or env-specific code should be provided via standard APIs in the EAL. | |
9 | ||
10 | By convention, a file is common if it is not located in a directory indicating that it is specific. | |
11 | For instance, a file located in a subdir of "x86_64" directory is specific to this architecture. | |
12 | A file located in a subdir of "linuxapp" is specific to this execution environment. | |
13 | ||
14 | .. note:: | |
15 | ||
16 | Code in DPDK libraries and applications should be generic. | |
17 | The correct location for architecture or executive environment specific code is in the EAL. | |
18 | ||
19 | When absolutely necessary, there are several ways to handle specific code: | |
20 | ||
21 | * Use a ``#ifdef`` with the CONFIG option in the C code. | |
22 | This can be done when the differences are small and they can be embedded in the same C file: | |
23 | ||
24 | .. code-block:: c | |
25 | ||
26 | #ifdef RTE_ARCH_I686 | |
27 | toto(); | |
28 | #else | |
29 | titi(); | |
30 | #endif | |
31 | ||
32 | * Use the CONFIG option in the Makefile. This is done when the differences are more significant. | |
33 | In this case, the code is split into two separate files that are architecture or environment specific. | |
34 | This should only apply inside the EAL library. | |
35 | ||
36 | .. note:: | |
37 | ||
38 | As in the linux kernel, the ``CONFIG_`` prefix is not used in C code. | |
39 | This is only needed in Makefiles or shell scripts. | |
40 | ||
41 | Per Architecture Sources | |
42 | ~~~~~~~~~~~~~~~~~~~~~~~~ | |
43 | ||
44 | The following config options can be used: | |
45 | ||
46 | * ``CONFIG_RTE_ARCH`` is a string that contains the name of the architecture. | |
47 | * ``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. | |
48 | ||
49 | Per Execution Environment Sources | |
50 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
51 | ||
52 | The following config options can be used: | |
53 | ||
54 | * ``CONFIG_RTE_EXEC_ENV`` is a string that contains the name of the executive environment. | |
55 | * ``CONFIG_RTE_EXEC_ENV_BSDAPP`` or ``CONFIG_RTE_EXEC_ENV_LINUXAPP`` are defined only if we are building for this execution environment. | |
56 | ||
57 | Library Statistics | |
58 | ------------------ | |
59 | ||
60 | Description | |
61 | ~~~~~~~~~~~ | |
62 | ||
63 | This document describes the guidelines for DPDK library-level statistics counter | |
64 | support. This includes guidelines for turning library statistics on and off and | |
65 | requirements for preventing ABI changes when implementing statistics. | |
66 | ||
67 | ||
68 | Mechanism to allow the application to turn library statistics on and off | |
69 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
70 | ||
71 | Each library that maintains statistics counters should provide a single build | |
72 | time flag that decides whether the statistics counter collection is enabled or | |
73 | not. This flag should be exposed as a variable within the DPDK configuration | |
74 | file. When this flag is set, all the counters supported by current library are | |
75 | collected for all the instances of every object type provided by the library. | |
76 | When this flag is cleared, none of the counters supported by the current library | |
77 | are collected for any instance of any object type provided by the library: | |
78 | ||
79 | .. code-block:: console | |
80 | ||
81 | # DPDK file config/common_linuxapp, config/common_bsdapp, etc. | |
82 | CONFIG_RTE_<LIBRARY_NAME>_STATS_COLLECT=y/n | |
83 | ||
84 | The default value for this DPDK configuration file variable (either "yes" or | |
85 | "no") is decided by each library. | |
86 | ||
87 | ||
88 | Prevention of ABI changes due to library statistics support | |
89 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
90 | ||
91 | The layout of data structures and prototype of functions that are part of the | |
92 | library API should not be affected by whether the collection of statistics | |
93 | counters is turned on or off for the current library. In practical terms, this | |
94 | means that space should always be allocated in the API data structures for | |
95 | statistics counters and the statistics related API functions are always built | |
96 | into the code, regardless of whether the statistics counter collection is turned | |
97 | on or off for the current library. | |
98 | ||
99 | When the collection of statistics counters for the current library is turned | |
100 | off, the counters retrieved through the statistics related API functions should | |
101 | have a default value of zero. | |
102 | ||
103 | ||
104 | Motivation to allow the application to turn library statistics on and off | |
105 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
106 | ||
107 | It is highly recommended that each library provides statistics counters to allow | |
108 | an application to monitor the library-level run-time events. Typical counters | |
109 | are: number of packets received/dropped/transmitted, number of buffers | |
110 | allocated/freed, number of occurrences for specific events, etc. | |
111 | ||
112 | However, the resources consumed for library-level statistics counter collection | |
113 | have to be spent out of the application budget and the counters collected by | |
114 | some libraries might not be relevant to the current application. In order to | |
115 | avoid any unwanted waste of resources and/or performance impacts, the | |
116 | application should decide at build time whether the collection of library-level | |
117 | statistics counters should be turned on or off for each library individually. | |
118 | ||
119 | Library-level statistics counters can be relevant or not for specific | |
120 | applications: | |
121 | ||
122 | * For Application A, counters maintained by Library X are always relevant and | |
123 | the application needs to use them to implement certain features, such as traffic | |
124 | accounting, logging, application-level statistics, etc. In this case, | |
125 | the application requires that collection of statistics counters for Library X is | |
126 | always turned on. | |
127 | ||
128 | * For Application B, counters maintained by Library X are only useful during the | |
129 | application debug stage and are not relevant once debug phase is over. In this | |
130 | case, the application may decide to turn on the collection of Library X | |
131 | statistics counters during the debug phase and at a later stage turn them off. | |
132 | ||
133 | * For Application C, counters maintained by Library X are not relevant at all. | |
134 | It might be that the application maintains its own set of statistics counters | |
135 | that monitor a different set of run-time events (e.g. number of connection | |
136 | requests, number of active users, etc). It might also be that the application | |
137 | uses multiple libraries (Library X, Library Y, etc) and it is interested in the | |
138 | statistics counters of Library Y, but not in those of Library X. In this case, | |
139 | the application may decide to turn the collection of statistics counters off for | |
140 | Library X and on for Library Y. | |
141 | ||
142 | The statistics collection consumes a certain amount of CPU resources (cycles, | |
143 | cache bandwidth, memory bandwidth, etc) that depends on: | |
144 | ||
145 | * Number of libraries used by the current application that have statistics | |
146 | counters collection turned on. | |
147 | ||
148 | * Number of statistics counters maintained by each library per object type | |
149 | instance (e.g. per port, table, pipeline, thread, etc). | |
150 | ||
151 | * Number of instances created for each object type supported by each library. | |
152 | ||
153 | * Complexity of the statistics logic collection for each counter: when only | |
154 | some occurrences of a specific event are valid, additional logic is typically | |
155 | needed to decide whether the current occurrence of the event should be counted | |
156 | or not. For example, in the event of packet reception, when only TCP packets | |
157 | with destination port within a certain range should be recorded, conditional | |
158 | branches are usually required. When processing a burst of packets that have been | |
159 | validated for header integrity, counting the number of bits set in a bitmask | |
160 | might be needed. |