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"title"><a id=
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19. Profile Mode
</h2></div></div></div><div class=
"toc"><p><b>Table of Contents
</b></p><dl><dt><span class=
"sect1"><a href=
"profile_mode.html#manual.ext.profile_mode.intro">Intro
</a></span></dt><dd><dl><dt><span class=
"sect2"><a href=
"profile_mode.html#manual.ext.profile_mode.using">Using the Profile Mode
</a></span></dt><dt><span class=
"sect2"><a href=
"profile_mode.html#manual.ext.profile_mode.tuning">Tuning the Profile Mode
</a></span></dt></dl></dd><dt><span class=
"sect1"><a href=
"bk01pt03ch19s02.html">Design
</a></span></dt><dd><dl><dt><span class=
"sect2"><a href=
"bk01pt03ch19s02.html#manual.ext.profile_mode.design.wrapper">Wrapper Model
</a></span></dt><dt><span class=
"sect2"><a href=
"bk01pt03ch19s02.html#manual.ext.profile_mode.design.instrumentation">Instrumentation
</a></span></dt><dt><span class=
"sect2"><a href=
"bk01pt03ch19s02.html#manual.ext.profile_mode.design.rtlib">Run Time Behavior
</a></span></dt><dt><span class=
"sect2"><a href=
"bk01pt03ch19s02.html#manual.ext.profile_mode.design.analysis">Analysis and Diagnostics
</a></span></dt><dt><span class=
"sect2"><a href=
"bk01pt03ch19s02.html#manual.ext.profile_mode.design.cost-model">Cost Model
</a></span></dt><dt><span class=
"sect2"><a href=
"bk01pt03ch19s02.html#manual.ext.profile_mode.design.reports">Reports
</a></span></dt><dt><span class=
"sect2"><a href=
"bk01pt03ch19s02.html#manual.ext.profile_mode.design.testing">Testing
</a></span></dt></dl></dd><dt><span class=
"sect1"><a href=
"bk01pt03ch19s03.html">Extensions for Custom Containers
</a></span></dt><dt><span class=
"sect1"><a href=
"bk01pt03ch19s04.html">Empirical Cost Model
</a></span></dt><dt><span class=
"sect1"><a href=
"bk01pt03ch19s05.html">Implementation Issues
</a></span></dt><dd><dl><dt><span class=
"sect2"><a href=
"bk01pt03ch19s05.html#manual.ext.profile_mode.implementation.stack">Stack Traces
</a></span></dt><dt><span class=
"sect2"><a href=
"bk01pt03ch19s05.html#manual.ext.profile_mode.implementation.symbols">Symbolization of Instruction Addresses
</a></span></dt><dt><span class=
"sect2"><a href=
"bk01pt03ch19s05.html#manual.ext.profile_mode.implementation.concurrency">Concurrency
</a></span></dt><dt><span class=
"sect2"><a href=
"bk01pt03ch19s05.html#manual.ext.profile_mode.implementation.stdlib-in-proflib">Using the Standard Library in the Instrumentation Implementation
</a></span></dt><dt><span class=
"sect2"><a href=
"bk01pt03ch19s05.html#manual.ext.profile_mode.implementation.malloc-hooks">Malloc Hooks
</a></span></dt><dt><span class=
"sect2"><a href=
"bk01pt03ch19s05.html#manual.ext.profile_mode.implementation.construction-destruction">Construction and Destruction of Global Objects
</a></span></dt></dl></dd><dt><span class=
"sect1"><a href=
"bk01pt03ch19s06.html">Developer Information
</a></span></dt><dd><dl><dt><span class=
"sect2"><a href=
"bk01pt03ch19s06.html#manual.ext.profile_mode.developer.bigpic">Big Picture
</a></span></dt><dt><span class=
"sect2"><a href=
"bk01pt03ch19s06.html#manual.ext.profile_mode.developer.howto">How To Add A Diagnostic
</a></span></dt></dl></dd><dt><span class=
"sect1"><a href=
"bk01pt03ch19s07.html">Diagnostics
</a></span></dt><dd><dl><dt><span class=
"sect2"><a href=
"bk01pt03ch19s07.html#manual.ext.profile_mode.analysis.template">Diagnostic Template
</a></span></dt><dt><span class=
"sect2"><a href=
"bk01pt03ch19s07.html#manual.ext.profile_mode.analysis.containers">Containers
</a></span></dt><dt><span class=
"sect2"><a href=
"bk01pt03ch19s07.html#manual.ext.profile_mode.analysis.algorithms">Algorithms
</a></span></dt><dt><span class=
"sect2"><a href=
"bk01pt03ch19s07.html#manual.ext.profile_mode.analysis.locality">Data Locality
</a></span></dt><dt><span class=
"sect2"><a href=
"bk01pt03ch19s07.html#manual.ext.profile_mode.analysis.mthread">Multithreaded Data Access
</a></span></dt><dt><span class=
"sect2"><a href=
"bk01pt03ch19s07.html#manual.ext.profile_mode.analysis.statistics">Statistics
</a></span></dt></dl></dd><dt><span class=
"bibliography"><a href=
"profile_mode.html#profile_mode.biblio">Bibliography
</a></span></dt></dl></div><div class=
"sect1" title=
"Intro"><div class=
"titlepage"><div><div><h2 class=
"title" style=
"clear: both"><a id=
"manual.ext.profile_mode.intro"></a>Intro
</h2></div></div></div><p>
7 <span class=
"emphasis"><em>Goal:
</em></span>Give performance improvement advice based on
8 recognition of suboptimal usage patterns of the standard library.
10 <span class=
"emphasis"><em>Method:
</em></span>Wrap the standard library code. Insert
11 calls to an instrumentation library to record the internal state of
12 various components at interesting entry/exit points to/from the standard
13 library. Process trace, recognize suboptimal patterns, give advice.
15 <a class=
"ulink" href=
"http://dx.doi.org/10.1109/CGO.2009.36" target=
"_top">paper presented at
18 <span class=
"emphasis"><em>Strengths:
</em></span>
19 </p><div class=
"itemizedlist"><ul class=
"itemizedlist" type=
"disc"><li class=
"listitem"><p>
20 Unintrusive solution. The application code does not require any
22 </p></li><li class=
"listitem"><p> The advice is call context sensitive, thus capable of
23 identifying precisely interesting dynamic performance behavior.
24 </p></li><li class=
"listitem"><p>
25 The overhead model is pay-per-view. When you turn off a diagnostic class
26 at compile time, its overhead disappears.
27 </p></li></ul></div><p>
29 <span class=
"emphasis"><em>Drawbacks:
</em></span>
30 </p><div class=
"itemizedlist"><ul class=
"itemizedlist" type=
"disc"><li class=
"listitem"><p>
31 You must recompile the application code with custom options.
32 </p></li><li class=
"listitem"><p>You must run the application on representative input.
33 The advice is input dependent.
34 </p></li><li class=
"listitem"><p>
35 The execution time will increase, in some cases by factors.
36 </p></li></ul></div><p>
37 </p><div class=
"sect2" title=
"Using the Profile Mode"><div class=
"titlepage"><div><div><h3 class=
"title"><a id=
"manual.ext.profile_mode.using"></a>Using the Profile Mode
</h3></div></div></div><p>
38 This is the anticipated common workflow for program
<code class=
"code">foo.cc
</code>:
39 </p><pre class=
"programlisting">
41 #include
<vector
>
44 for (int k =
0; k
< 1024; ++k) v.insert(v.begin(), k);
47 $ g++ -D_GLIBCXX_PROFILE foo.cc
49 $ cat libstdcxx-profile.txt
50 vector-to-list: improvement =
5: call stack =
0x804842c ...
51 : advice = change std::vector to std::list
52 vector-size: improvement =
3: call stack =
0x804842c ...
53 : advice = change initial container size from
0 to
1024
57 </p><div class=
"itemizedlist"><ul class=
"itemizedlist" type=
"disc"><li class=
"listitem"><p>
58 Warning id. This is a short descriptive string for the class
59 that this warning belongs to. E.g.,
"vector-to-list".
60 </p></li><li class=
"listitem"><p>
61 Estimated improvement. This is an approximation of the benefit expected
62 from implementing the change suggested by the warning. It is given on
63 a log10 scale. Negative values mean that the alternative would actually
64 do worse than the current choice.
65 In the example above,
5 comes from the fact that the overhead of
66 inserting at the beginning of a vector vs. a list is around
1024 *
1024 /
2,
67 which is around
10e5. The improvement from setting the initial size to
68 1024 is in the range of
10e3, since the overhead of dynamic resizing is
70 </p></li><li class=
"listitem"><p>
71 Call stack. Currently, the addresses are printed without
72 symbol name or code location attribution.
73 Users are expected to postprocess the output using, for instance, addr2line.
74 </p></li><li class=
"listitem"><p>
75 The warning message. For some warnings, this is static text, e.g.,
76 "change vector to list". For other warnings, such as the one above,
77 the message contains numeric advice, e.g., the suggested initial size
79 </p></li></ul></div><p>
80 </p><p>Three files are generated.
<code class=
"code">libstdcxx-profile.txt
</code>
81 contains human readable advice.
<code class=
"code">libstdcxx-profile.raw
</code>
82 contains implementation specific data about each diagnostic.
83 Their format is not documented. They are sufficient to generate
84 all the advice given in
<code class=
"code">libstdcxx-profile.txt
</code>. The advantage
85 of keeping this raw format is that traces from multiple executions can
86 be aggregated simply by concatenating the raw traces. We intend to
87 offer an external utility program that can issue advice from a trace.
88 <code class=
"code">libstdcxx-profile.conf.out
</code> lists the actual diagnostic
89 parameters used. To alter parameters, edit this file and rename it to
90 <code class=
"code">libstdcxx-profile.conf
</code>.
91 </p><p>Advice is given regardless whether the transformation is valid.
92 For instance, we advise changing a map to an unordered_map even if the
93 application semantics require that data be ordered.
94 We believe such warnings can help users understand the performance
95 behavior of their application better, which can lead to changes
96 at a higher abstraction level.
97 </p></div><div class=
"sect2" title=
"Tuning the Profile Mode"><div class=
"titlepage"><div><div><h3 class=
"title"><a id=
"manual.ext.profile_mode.tuning"></a>Tuning the Profile Mode
</h3></div></div></div><p>Compile time switches and environment variables (see also file
98 profiler.h). Unless specified otherwise, they can be set at compile time
99 using -D_
<name
> or by setting variable
<name
>
100 in the environment where the program is run, before starting execution.
101 </p><div class=
"itemizedlist"><ul class=
"itemizedlist" type=
"disc"><li class=
"listitem"><p>
102 <code class=
"code">_GLIBCXX_PROFILE_NO_
<diagnostic
></code>:
103 disable specific diagnostics.
104 See section Diagnostics for possible values.
105 (Environment variables not supported.)
106 </p></li><li class=
"listitem"><p>
107 <code class=
"code">_GLIBCXX_PROFILE_TRACE_PATH_ROOT
</code>: set an alternative root
108 path for the output files.
109 </p></li><li class=
"listitem"><p>_GLIBCXX_PROFILE_MAX_WARN_COUNT: set it to the maximum
110 number of warnings desired. The default value is
10.
</p></li><li class=
"listitem"><p>
111 <code class=
"code">_GLIBCXX_PROFILE_MAX_STACK_DEPTH
</code>: if set to
0,
113 be collected and reported for the program as a whole, and not for each
115 This could also be used in continuous regression tests, where you
116 just need to know whether there is a regression or not.
117 The default value is
32.
118 </p></li><li class=
"listitem"><p>
119 <code class=
"code">_GLIBCXX_PROFILE_MEM_PER_DIAGNOSTIC
</code>:
120 set a limit on how much memory to use for the accounting tables for each
121 diagnostic type. When this limit is reached, new events are ignored
122 until the memory usage decreases under the limit. Generally, this means
123 that newly created containers will not be instrumented until some
124 live containers are deleted. The default is
128 MB.
125 </p></li><li class=
"listitem"><p>
126 <code class=
"code">_GLIBCXX_PROFILE_NO_THREADS
</code>:
127 Make the library not use threads. If thread local storage (TLS) is not
128 available, you will get a preprocessor error asking you to set
129 -D_GLIBCXX_PROFILE_NO_THREADS if your program is single-threaded.
130 Multithreaded execution without TLS is not supported.
131 (Environment variable not supported.)
132 </p></li><li class=
"listitem"><p>
133 <code class=
"code">_GLIBCXX_HAVE_EXECINFO_H
</code>:
134 This name should be defined automatically at library configuration time.
135 If your library was configured without
<code class=
"code">execinfo.h
</code>, but
136 you have it in your include path, you can define it explicitly. Without
137 it, advice is collected for the program as a whole, and not for each
139 (Environment variable not supported.)
140 </p></li></ul></div><p>
141 </p></div></div><div class=
"bibliography" title=
"Bibliography"><div class=
"titlepage"><div><div><h2 class=
"title"><a id=
"profile_mode.biblio"></a>Bibliography
</h2></div></div></div><div class=
"biblioentry" title=
"Perflint: A Context Sensitive Performance Advisor for C++ Programs"><a id=
"id508157"></a><p><span class=
"title"><i>
142 Perflint: A Context Sensitive Performance Advisor for C++ Programs
143 </i>.
</span><span class=
"author"><span class=
"firstname">Lixia
</span> <span class=
"surname">Liu
</span>.
</span><span class=
"author"><span class=
"firstname">Silvius
</span> <span class=
"surname">Rus
</span>.
</span><span class=
"copyright">Copyright ©
2009 .
</span><span class=
"publisher"><span class=
"publishername">
144 Proceedings of the
2009 International Symposium on Code Generation
146 .
</span></span></p></div></div></div><div class=
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