gprof

To use gprof, simply recompile your program with gcc using the -pg switch. This option causes gcc to insert a bit of extra code into the beginning of each subroutine in your program. The -pg switch must also be used when you link your program, since another snippet of code must be present to tie the pieces together.

After recompiling, run your program. It will execute slightly slower because of the work needed to profile the code, but it shouldn't be too slow. After the program finishes, there will be a file named gmon.out in the current directory. This file contains the profiling information collected during the program's run. gprof is used to print this in a human readable form.

gprof outputs information in two ways: a flat profile and a call graph. The flat profile tells you how much time the program spent in all of the subroutines, and the call graph tells you which subroutines called which subroutines.

The other profiler in common use on Linux is bprof. The major difference between bprof and gprof is that bprof gives timings on a source line basis while gprof has only subroutine-level resolution, and also includes information like invocation counts. To use bprof, link an object file, bprof.o, into your program. After you've run your program, a file named bmon.out contains the timing information. Run bprof on this data file, and it makes copies of your source files with timing numbers prepended to each line.

How it works. Call stack sampling. Gprof samples the system call stack at regular intervals. It records which functions are on the call stack, and accumulates counts + interval times for each function.