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   4   Extensions
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   6 </th><td width="20%" 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"></a>Chapter 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.
   9   </p><p>
  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.
  14   For details, see
  15   <a class="ulink" href="http://dx.doi.org/10.1109/CGO.2009.36" target="_top">paper presented at
  16    CGO 2009</a>.
  17   </p><p>
  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
  21   modification.
  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>
  28   </p><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">
  40 $ cat foo.cc
  41 #include &lt;vector&gt;
  42 int main() {
  43   vector&lt;int&gt; v;
  44   for (int k = 0; k &lt; 1024; ++k) v.insert(v.begin(), k);
  45 }
  46
  47 $ g++ -D_GLIBCXX_PROFILE foo.cc
  48 $ ./a.out
  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
  54 </pre><p>
  55   </p><p>
  56   Anatomy of a warning:
  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
  69   linear in this case.
  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
  78   of the vector.
  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_&lt;name&gt; or by setting variable &lt;name&gt;
 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_&lt;diagnostic&gt;</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,
 112    the advice will
 113    be collected and reported for the program as a whole, and not for each
 114    call context.
 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
 138    call context.
 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="id486510"></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
 145         and Optimization
 146       . </span></span></p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="bk01pt03ch18s05.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="extensions.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="bk01pt03ch19s02.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Testing </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Design</td></tr></table></div></body></html>