(gprof.info) Introduction

 
 Introduction to Profiling
 *************************
 
    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.
 
    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.
 
    Profiling has several steps:
 
    * You must compile and link your program with profiling enabled.
       Compiling.
 
    * You must execute your program to generate a profile data file.
       Executing.
 
    * You must run `gprof' to analyze the profile data.  
      Invoking.
 
    The next three chapters explain these steps in greater detail.
 
    Several forms of output are available from the analysis.
 
    The "flat profile" 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.   Flat Profile.
 
    The "call graph" 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.   Call Graph.
 
    The "annotated source" listing is a copy of the program's source
 code, labeled with the number of times each line of the program was
 executed.   Annotated Source.
 
    To better understand how profiling works, you may wish to read a
 description of its implementation.   Implementation.
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