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| <h2 class="chapter">1 Introduction to Profiling</h2> |
| |
| <p>Profiling allows you to learn where your program spent its time and which |
| functions called which other functions while it was executing. This |
| information can show you which pieces of your program are slower than you |
| expected, and might be candidates for rewriting to make your program |
| execute faster. It can also tell you which functions are being called more |
| or less often than you expected. This may help you spot bugs that had |
| otherwise been unnoticed. |
| |
| <p>Since the profiler uses information collected during the actual execution |
| of your program, it can be used on programs that are too large or too |
| complex to analyze by reading the source. However, how your program is run |
| will affect the information that shows up in the profile data. If you |
| don't use some feature of your program while it is being profiled, no |
| profile information will be generated for that feature. |
| |
| <p>Profiling has several steps: |
| |
| <ul> |
| <li>You must compile and link your program with profiling enabled. |
| See <a href="Compiling.html#Compiling">Compiling a Program for Profiling</a>. |
| |
| <li>You must execute your program to generate a profile data file. |
| See <a href="Executing.html#Executing">Executing the Program</a>. |
| |
| <li>You must run <code>gprof</code> to analyze the profile data. |
| See <a href="Invoking.html#Invoking"><code>gprof</code> Command Summary</a>. |
| </ul> |
| |
| <p>The next three chapters explain these steps in greater detail. |
| |
| <!-- man begin DESCRIPTION --> |
| <p>Several forms of output are available from the analysis. |
| |
| <p>The <dfn>flat profile</dfn> shows how much time your program spent in each function, |
| and how many times that function was called. If you simply want to know |
| which functions burn most of the cycles, it is stated concisely here. |
| See <a href="Flat-Profile.html#Flat-Profile">The Flat Profile</a>. |
| |
| <p>The <dfn>call graph</dfn> shows, for each function, which functions called it, which |
| other functions it called, and how many times. There is also an estimate |
| of how much time was spent in the subroutines of each function. This can |
| suggest places where you might try to eliminate function calls that use a |
| lot of time. See <a href="Call-Graph.html#Call-Graph">The Call Graph</a>. |
| |
| <p>The <dfn>annotated source</dfn> listing is a copy of the program's |
| source code, labeled with the number of times each line of the |
| program was executed. See <a href="Annotated-Source.html#Annotated-Source">The Annotated Source Listing</a>. |
| <!-- man end --> |
| |
| <p>To better understand how profiling works, you may wish to read |
| a description of its implementation. |
| See <a href="Implementation.html#Implementation">Implementation of Profiling</a>. |
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