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| author | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
|---|---|---|
| committer | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
| commit | 554fd8c5195424bdbcabf5de30fdc183aba391bd (patch) | |
| tree | 976dc5ab7fddf506dadce60ae936f43f58787092 /libstdc++-v3/doc/html/manual/bk01pt03ch19s02.html | |
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diff --git a/libstdc++-v3/doc/html/manual/bk01pt03ch19s02.html b/libstdc++-v3/doc/html/manual/bk01pt03ch19s02.html new file mode 100644 index 000000000..ce915ddb5 --- /dev/null +++ b/libstdc++-v3/doc/html/manual/bk01pt03ch19s02.html @@ -0,0 +1,122 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Design</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="profile_mode.html" title="Chapter 19. Profile Mode"/><link rel="prev" href="profile_mode.html" title="Chapter 19. Profile Mode"/><link rel="next" href="bk01pt03ch19s03.html" title="Extensions for Custom Containers"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Design</th></tr><tr><td align="left"><a accesskey="p" href="profile_mode.html">Prev</a> </td><th width="60%" align="center">Chapter 19. Profile Mode</th><td align="right"> <a accesskey="n" href="bk01pt03ch19s03.html">Next</a></td></tr></table><hr/></div><div class="section" title="Design"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.profile_mode.design"/>Design</h2></div></div></div><p> +</p><div class="table"><a id="id486504"/><p class="title"><strong>Table 19.1. Profile Code Location</strong></p><div class="table-contents"><table summary="Profile Code Location" border="1"><colgroup><col style="text-align: left" class="c1"/><col style="text-align: left" class="c2"/></colgroup><thead><tr><th style="text-align: left">Code Location</th><th style="text-align: left">Use</th></tr></thead><tbody><tr><td style="text-align: left"><code class="code">libstdc++-v3/include/std/*</code></td><td style="text-align: left">Preprocessor code to redirect to profile extension headers.</td></tr><tr><td style="text-align: left"><code class="code">libstdc++-v3/include/profile/*</code></td><td style="text-align: left">Profile extension public headers (map, vector, ...).</td></tr><tr><td style="text-align: left"><code class="code">libstdc++-v3/include/profile/impl/*</code></td><td style="text-align: left">Profile extension internals. Implementation files are + only included from <code class="code">impl/profiler.h</code>, which is the only + file included from the public headers.</td></tr></tbody></table></div></div><br class="table-break"/><p> +</p><div class="section" title="Wrapper Model"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.profile_mode.design.wrapper"/>Wrapper Model</h3></div></div></div><p> + In order to get our instrumented library version included instead of the + release one, + we use the same wrapper model as the debug mode. + We subclass entities from the release version. Wherever + <code class="code">_GLIBCXX_PROFILE</code> is defined, the release namespace is + <code class="code">std::__norm</code>, whereas the profile namespace is + <code class="code">std::__profile</code>. Using plain <code class="code">std</code> translates + into <code class="code">std::__profile</code>. + </p><p> + Whenever possible, we try to wrap at the public interface level, e.g., + in <code class="code">unordered_set</code> rather than in <code class="code">hashtable</code>, + in order not to depend on implementation. + </p><p> + Mixing object files built with and without the profile mode must + not affect the program execution. However, there are no guarantees to + the accuracy of diagnostics when using even a single object not built with + <code class="code">-D_GLIBCXX_PROFILE</code>. + Currently, mixing the profile mode with debug and parallel extensions is + not allowed. Mixing them at compile time will result in preprocessor errors. + Mixing them at link time is undefined. + </p></div><div class="section" title="Instrumentation"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.profile_mode.design.instrumentation"/>Instrumentation</h3></div></div></div><p> + Instead of instrumenting every public entry and exit point, + we chose to add instrumentation on demand, as needed + by individual diagnostics. + The main reason is that some diagnostics require us to extract bits of + internal state that are particular only to that diagnostic. + We plan to formalize this later, after we learn more about the requirements + of several diagnostics. + </p><p> + All the instrumentation points can be switched on and off using + <code class="code">-D[_NO]_GLIBCXX_PROFILE_<diagnostic></code> options. + With all the instrumentation calls off, there should be negligible + overhead over the release version. This property is needed to support + diagnostics based on timing of internal operations. For such diagnostics, + we anticipate turning most of the instrumentation off in order to prevent + profiling overhead from polluting time measurements, and thus diagnostics. + </p><p> + All the instrumentation on/off compile time switches live in + <code class="code">include/profile/profiler.h</code>. + </p></div><div class="section" title="Run Time Behavior"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.profile_mode.design.rtlib"/>Run Time Behavior</h3></div></div></div><p> + For practical reasons, the instrumentation library processes the trace + partially + rather than dumping it to disk in raw form. Each event is processed when + it occurs. It is usually attached a cost and it is aggregated into + the database of a specific diagnostic class. The cost model + is based largely on the standard performance guarantees, but in some + cases we use knowledge about GCC's standard library implementation. + </p><p> + Information is indexed by (1) call stack and (2) instance id or address + to be able to understand and summarize precise creation-use-destruction + dynamic chains. Although the analysis is sensitive to dynamic instances, + the reports are only sensitive to call context. Whenever a dynamic instance + is destroyed, we accumulate its effect to the corresponding entry for the + call stack of its constructor location. + </p><p> + For details, see + <a class="link" href="http://dx.doi.org/10.1109/CGO.2009.36">paper presented at + CGO 2009</a>. + </p></div><div class="section" title="Analysis and Diagnostics"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.profile_mode.design.analysis"/>Analysis and Diagnostics</h3></div></div></div><p> + Final analysis takes place offline, and it is based entirely on the + generated trace and debugging info in the application binary. + See section Diagnostics for a list of analysis types that we plan to support. + </p><p> + The input to the analysis is a table indexed by profile type and call stack. + The data type for each entry depends on the profile type. + </p></div><div class="section" title="Cost Model"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.profile_mode.design.cost-model"/>Cost Model</h3></div></div></div><p> + While it is likely that cost models become complex as we get into + more sophisticated analysis, we will try to follow a simple set of rules + at the beginning. + </p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p><span class="emphasis"><em>Relative benefit estimation:</em></span> + The idea is to estimate or measure the cost of all operations + in the original scenario versus the scenario we advise to switch to. + For instance, when advising to change a vector to a list, an occurrence + of the <code class="code">insert</code> method will generally count as a benefit. + Its magnitude depends on (1) the number of elements that get shifted + and (2) whether it triggers a reallocation. + </p></li><li class="listitem"><p><span class="emphasis"><em>Synthetic measurements:</em></span> + We will measure the relative difference between similar operations on + different containers. We plan to write a battery of small tests that + compare the times of the executions of similar methods on different + containers. The idea is to run these tests on the target machine. + If this training phase is very quick, we may decide to perform it at + library initialization time. The results can be cached on disk and reused + across runs. + </p></li><li class="listitem"><p><span class="emphasis"><em>Timers:</em></span> + We plan to use timers for operations of larger granularity, such as sort. + For instance, we can switch between different sort methods on the fly + and report the one that performs best for each call context. + </p></li><li class="listitem"><p><span class="emphasis"><em>Show stoppers:</em></span> + We may decide that the presence of an operation nullifies the advice. + For instance, when considering switching from <code class="code">set</code> to + <code class="code">unordered_set</code>, if we detect use of operator <code class="code">++</code>, + we will simply not issue the advice, since this could signal that the use + care require a sorted container.</p></li></ul></div></div><div class="section" title="Reports"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.profile_mode.design.reports"/>Reports</h3></div></div></div><p> +There are two types of reports. First, if we recognize a pattern for which +we have a substitute that is likely to give better performance, we print +the advice and estimated performance gain. The advice is usually associated +to a code position and possibly a call stack. + </p><p> +Second, we report performance characteristics for which we do not have +a clear solution for improvement. For instance, we can point to the user +the top 10 <code class="code">multimap</code> locations +which have the worst data locality in actual traversals. +Although this does not offer a solution, +it helps the user focus on the key problems and ignore the uninteresting ones. + </p></div><div class="section" title="Testing"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.profile_mode.design.testing"/>Testing</h3></div></div></div><p> + First, we want to make sure we preserve the behavior of the release mode. + You can just type <code class="code">"make check-profile"</code>, which + builds and runs the whole test suite in profile mode. + </p><p> + Second, we want to test the correctness of each diagnostic. + We created a <code class="code">profile</code> directory in the test suite. + Each diagnostic must come with at least two tests, one for false positives + and one for false negatives. + </p></div></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="profile_mode.html">Prev</a> </td><td align="center"><a accesskey="u" href="profile_mode.html">Up</a></td><td align="right"> <a accesskey="n" href="bk01pt03ch19s03.html">Next</a></td></tr><tr><td align="left" valign="top">Chapter 19. Profile Mode </td><td align="center"><a accesskey="h" href="../spine.html">Home</a></td><td align="right" valign="top"> Extensions for Custom Containers</td></tr></table></div></body></html> |