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104 lines
4.5 KiB
HTML
<html lang="en">
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<title>Introduction - GNU gprof</title>
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<link rel="next" href="Compiling.html#Compiling" title="Compiling">
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<!--
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This file documents the gprof profiler of the GNU system.
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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<div class="node">
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<a name="Introduction"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Compiling.html#Compiling">Compiling</a>,
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Previous: <a rel="previous" accesskey="p" href="index.html#Top">Top</a>,
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Up: <a rel="up" accesskey="u" href="index.html#Top">Top</a>
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<hr>
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</div>
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<h2 class="chapter">1 Introduction to Profiling</h2>
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<p>Profiling allows you to learn where your program spent its time and which
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functions called which other functions while it was executing. This
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information can show you which pieces of your program are slower than you
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expected, and might be candidates for rewriting to make your program
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execute faster. It can also tell you which functions are being called more
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or less often than you expected. This may help you spot bugs that had
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otherwise been unnoticed.
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<p>Since the profiler uses information collected during the actual execution
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of your program, it can be used on programs that are too large or too
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complex to analyze by reading the source. However, how your program is run
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will affect the information that shows up in the profile data. If you
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don't use some feature of your program while it is being profiled, no
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profile information will be generated for that feature.
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<p>Profiling has several steps:
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<ul>
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<li>You must compile and link your program with profiling enabled.
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See <a href="Compiling.html#Compiling">Compiling a Program for Profiling</a>.
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<li>You must execute your program to generate a profile data file.
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See <a href="Executing.html#Executing">Executing the Program</a>.
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<li>You must run <code>gprof</code> to analyze the profile data.
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See <a href="Invoking.html#Invoking"><code>gprof</code> Command Summary</a>.
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</ul>
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<p>The next three chapters explain these steps in greater detail.
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<!-- man begin DESCRIPTION -->
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<p>Several forms of output are available from the analysis.
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<p>The <dfn>flat profile</dfn> shows how much time your program spent in each function,
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and how many times that function was called. If you simply want to know
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which functions burn most of the cycles, it is stated concisely here.
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See <a href="Flat-Profile.html#Flat-Profile">The Flat Profile</a>.
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<p>The <dfn>call graph</dfn> shows, for each function, which functions called it, which
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other functions it called, and how many times. There is also an estimate
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of how much time was spent in the subroutines of each function. This can
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suggest places where you might try to eliminate function calls that use a
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lot of time. See <a href="Call-Graph.html#Call-Graph">The Call Graph</a>.
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<p>The <dfn>annotated source</dfn> listing is a copy of the program's
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source code, labeled with the number of times each line of the
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program was executed. See <a href="Annotated-Source.html#Annotated-Source">The Annotated Source Listing</a>.
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<!-- man end -->
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<p>To better understand how profiling works, you may wish to read
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a description of its implementation.
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See <a href="Implementation.html#Implementation">Implementation of Profiling</a>.
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</body></html>
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