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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Chapter 19. Profile Mode</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.76.1"/><meta name="keywords" content=" C++ , library , profile "/><meta name="keywords" content=" ISO C++ , library "/><link rel="home" href="../spine.html" title="The GNU C++ Library"/><link rel="up" href="extensions.html" title="Part III. Extensions"/><link rel="prev" href="bk01pt03ch18s05.html" title="Testing"/><link rel="next" href="bk01pt03ch19s02.html" title="Design"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 19. Profile Mode</th></tr><tr><td align="left"><a accesskey="p" href="bk01pt03ch18s05.html">Prev</a> </td><th width="60%" align="center">Part III.
Extensions
</th><td align="right"> <a accesskey="n" href="bk01pt03ch19s02.html">Next</a></td></tr></table><hr/></div><div class="chapter" title="Chapter 19. Profile Mode"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.profile_mode"/>Chapter 19. Profile Mode</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl><dt><span class="section"><a href="profile_mode.html#manual.ext.profile_mode.intro">Intro</a></span></dt><dd><dl><dt><span class="section"><a href="profile_mode.html#manual.ext.profile_mode.using">Using the Profile Mode</a></span></dt><dt><span class="section"><a href="profile_mode.html#manual.ext.profile_mode.tuning">Tuning the Profile Mode</a></span></dt></dl></dd><dt><span class="section"><a href="bk01pt03ch19s02.html">Design</a></span></dt><dd><dl><dt><span class="section"><a href="bk01pt03ch19s02.html#manual.ext.profile_mode.design.wrapper">Wrapper Model</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s02.html#manual.ext.profile_mode.design.instrumentation">Instrumentation</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s02.html#manual.ext.profile_mode.design.rtlib">Run Time Behavior</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s02.html#manual.ext.profile_mode.design.analysis">Analysis and Diagnostics</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s02.html#manual.ext.profile_mode.design.cost-model">Cost Model</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s02.html#manual.ext.profile_mode.design.reports">Reports</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s02.html#manual.ext.profile_mode.design.testing">Testing</a></span></dt></dl></dd><dt><span class="section"><a href="bk01pt03ch19s03.html">Extensions for Custom Containers</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s04.html">Empirical Cost Model</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s05.html">Implementation Issues</a></span></dt><dd><dl><dt><span class="section"><a href="bk01pt03ch19s05.html#manual.ext.profile_mode.implementation.stack">Stack Traces</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s05.html#manual.ext.profile_mode.implementation.symbols">Symbolization of Instruction Addresses</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s05.html#manual.ext.profile_mode.implementation.concurrency">Concurrency</a></span></dt><dt><span class="section"><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="section"><a href="bk01pt03ch19s05.html#manual.ext.profile_mode.implementation.malloc-hooks">Malloc Hooks</a></span></dt><dt><span class="section"><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="section"><a href="bk01pt03ch19s06.html">Developer Information</a></span></dt><dd><dl><dt><span class="section"><a href="bk01pt03ch19s06.html#manual.ext.profile_mode.developer.bigpic">Big Picture</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s06.html#manual.ext.profile_mode.developer.howto">How To Add A Diagnostic</a></span></dt></dl></dd><dt><span class="section"><a href="bk01pt03ch19s07.html">Diagnostics</a></span></dt><dd><dl><dt><span class="section"><a href="bk01pt03ch19s07.html#manual.ext.profile_mode.analysis.template">Diagnostic Template</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s07.html#manual.ext.profile_mode.analysis.containers">Containers</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s07.html#manual.ext.profile_mode.analysis.algorithms">Algorithms</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s07.html#manual.ext.profile_mode.analysis.locality">Data Locality</a></span></dt><dt><span class="section"><a href="bk01pt03ch19s07.html#manual.ext.profile_mode.analysis.mthread">Multithreaded Data Access</a></span></dt><dt><span class="section"><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="section" title="Intro"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.profile_mode.intro"/>Intro</h2></div></div></div><p>
<span class="emphasis"><em>Goal: </em></span>Give performance improvement advice based on
recognition of suboptimal usage patterns of the standard library.
</p><p>
<span class="emphasis"><em>Method: </em></span>Wrap the standard library code. Insert
calls to an instrumentation library to record the internal state of
various components at interesting entry/exit points to/from the standard
library. Process trace, recognize suboptimal patterns, give advice.
For details, see
<a class="link" href="http://dx.doi.org/10.1109/CGO.2009.36">paper presented at
CGO 2009</a>.
</p><p>
<span class="emphasis"><em>Strengths: </em></span>
</p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p>
Unintrusive solution. The application code does not require any
modification.
</p></li><li class="listitem"><p> The advice is call context sensitive, thus capable of
identifying precisely interesting dynamic performance behavior.
</p></li><li class="listitem"><p>
The overhead model is pay-per-view. When you turn off a diagnostic class
at compile time, its overhead disappears.
</p></li></ul></div><p>
</p><p>
<span class="emphasis"><em>Drawbacks: </em></span>
</p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p>
You must recompile the application code with custom options.
</p></li><li class="listitem"><p>You must run the application on representative input.
The advice is input dependent.
</p></li><li class="listitem"><p>
The execution time will increase, in some cases by factors.
</p></li></ul></div><p>
</p><div class="section" title="Using the Profile Mode"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.profile_mode.using"/>Using the Profile Mode</h3></div></div></div><p>
This is the anticipated common workflow for program <code class="code">foo.cc</code>:
</p><pre class="programlisting">
$ cat foo.cc
#include <vector>
int main() {
vector<int> v;
for (int k = 0; k < 1024; ++k) v.insert(v.begin(), k);
}
$ g++ -D_GLIBCXX_PROFILE foo.cc
$ ./a.out
$ cat libstdcxx-profile.txt
vector-to-list: improvement = 5: call stack = 0x804842c ...
: advice = change std::vector to std::list
vector-size: improvement = 3: call stack = 0x804842c ...
: advice = change initial container size from 0 to 1024
</pre><p>
</p><p>
Anatomy of a warning:
</p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p>
Warning id. This is a short descriptive string for the class
that this warning belongs to. E.g., "vector-to-list".
</p></li><li class="listitem"><p>
Estimated improvement. This is an approximation of the benefit expected
from implementing the change suggested by the warning. It is given on
a log10 scale. Negative values mean that the alternative would actually
do worse than the current choice.
In the example above, 5 comes from the fact that the overhead of
inserting at the beginning of a vector vs. a list is around 1024 * 1024 / 2,
which is around 10e5. The improvement from setting the initial size to
1024 is in the range of 10e3, since the overhead of dynamic resizing is
linear in this case.
</p></li><li class="listitem"><p>
Call stack. Currently, the addresses are printed without
symbol name or code location attribution.
Users are expected to postprocess the output using, for instance, addr2line.
</p></li><li class="listitem"><p>
The warning message. For some warnings, this is static text, e.g.,
"change vector to list". For other warnings, such as the one above,
the message contains numeric advice, e.g., the suggested initial size
of the vector.
</p></li></ul></div><p>
</p><p>Three files are generated. <code class="code">libstdcxx-profile.txt</code>
contains human readable advice. <code class="code">libstdcxx-profile.raw</code>
contains implementation specific data about each diagnostic.
Their format is not documented. They are sufficient to generate
all the advice given in <code class="code">libstdcxx-profile.txt</code>. The advantage
of keeping this raw format is that traces from multiple executions can
be aggregated simply by concatenating the raw traces. We intend to
offer an external utility program that can issue advice from a trace.
<code class="code">libstdcxx-profile.conf.out</code> lists the actual diagnostic
parameters used. To alter parameters, edit this file and rename it to
<code class="code">libstdcxx-profile.conf</code>.
</p><p>Advice is given regardless whether the transformation is valid.
For instance, we advise changing a map to an unordered_map even if the
application semantics require that data be ordered.
We believe such warnings can help users understand the performance
behavior of their application better, which can lead to changes
at a higher abstraction level.
</p></div><div class="section" title="Tuning the Profile Mode"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.profile_mode.tuning"/>Tuning the Profile Mode</h3></div></div></div><p>Compile time switches and environment variables (see also file
profiler.h). Unless specified otherwise, they can be set at compile time
using -D_<name> or by setting variable <name>
in the environment where the program is run, before starting execution.
</p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p>
<code class="code">_GLIBCXX_PROFILE_NO_<diagnostic></code>:
disable specific diagnostics.
See section Diagnostics for possible values.
(Environment variables not supported.)
</p></li><li class="listitem"><p>
<code class="code">_GLIBCXX_PROFILE_TRACE_PATH_ROOT</code>: set an alternative root
path for the output files.
</p></li><li class="listitem"><p>_GLIBCXX_PROFILE_MAX_WARN_COUNT: set it to the maximum
number of warnings desired. The default value is 10.</p></li><li class="listitem"><p>
<code class="code">_GLIBCXX_PROFILE_MAX_STACK_DEPTH</code>: if set to 0,
the advice will
be collected and reported for the program as a whole, and not for each
call context.
This could also be used in continuous regression tests, where you
just need to know whether there is a regression or not.
The default value is 32.
</p></li><li class="listitem"><p>
<code class="code">_GLIBCXX_PROFILE_MEM_PER_DIAGNOSTIC</code>:
set a limit on how much memory to use for the accounting tables for each
diagnostic type. When this limit is reached, new events are ignored
until the memory usage decreases under the limit. Generally, this means
that newly created containers will not be instrumented until some
live containers are deleted. The default is 128 MB.
</p></li><li class="listitem"><p>
<code class="code">_GLIBCXX_PROFILE_NO_THREADS</code>:
Make the library not use threads. If thread local storage (TLS) is not
available, you will get a preprocessor error asking you to set
-D_GLIBCXX_PROFILE_NO_THREADS if your program is single-threaded.
Multithreaded execution without TLS is not supported.
(Environment variable not supported.)
</p></li><li class="listitem"><p>
<code class="code">_GLIBCXX_HAVE_EXECINFO_H</code>:
This name should be defined automatically at library configuration time.
If your library was configured without <code class="code">execinfo.h</code>, but
you have it in your include path, you can define it explicitly. Without
it, advice is collected for the program as a whole, and not for each
call context.
(Environment variable not supported.)
</p></li></ul></div><p>
</p></div></div><div class="bibliography" title="Bibliography"><div class="titlepage"><div><div><h2 class="title"><a id="profile_mode.biblio"/>Bibliography</h2></div></div></div><div class="biblioentry"><a id="id489940"/><p><span class="citetitle"><em class="citetitle">
Perflint: A Context Sensitive Performance Advisor for C++ Programs
</em>. </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">
Proceedings of the 2009 International Symposium on Code Generation
and Optimization
. </span></span></p></div></div></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="bk01pt03ch18s05.html">Prev</a> </td><td align="center"><a accesskey="u" href="extensions.html">Up</a></td><td align="right"> <a accesskey="n" href="bk01pt03ch19s02.html">Next</a></td></tr><tr><td align="left" valign="top">Testing </td><td align="center"><a accesskey="h" href="../spine.html">Home</a></td><td align="right" valign="top"> Design</td></tr></table></div></body></html>
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