This manual describes the GNU profiler, gprof, and how you
can use it to determine which parts of a program are taking most of the
execution time. We assume that you know how to write, compile, and
execute programs. GNU gprof was written by Jay Fenlason.
This manual was edited January 1993 by Jeffrey Osier.
Copyright (C) 1988, 1992 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.
Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.
Permission is granted to copy and distribute translations of this manual into another language, under the same conditions as for modified versions.
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:
gprof to analyze the profile data.
See section gprof Command Summary.
The next three chapters explain these steps in greater detail.
The result of the analysis is a file containing two tables, the flat profile and the call graph (plus blurbs which briefly explain the contents of these tables).
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. See section How to Understand the 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. See section How to Read the Call Graph.