GNU gprof: How do I?

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7 Answers to Common Questions

How can I get more exact information about hot spots in my program?

Looking at the per-line call counts only tells part of the story. Because gprof can only report call times and counts by function, the best way to get finer-grained information on where the program is spending its time is to re-factor large functions into sequences of calls to smaller ones. Beware however that this can introduce artificial hot spots since compiling with ‘-pg’ adds a significant overhead to function calls. An alternative solution is to use a non-intrusive profiler, e.g. oprofile.

How do I find which lines in my program were executed the most times?

Use the gcov program.

How do I find which lines in my program called a particular function?

Use ‘gprof -l’ and lookup the function in the call graph. The callers will be broken down by function and line number.

How do I analyze a program that runs for less than a second?

Try using a shell script like this one:

for i in `seq 1 100`; do
  fastprog
  mv gmon.out gmon.out.$i
done
gprof -s fastprog gmon.out.*
gprof fastprog gmon.sum

If your program is completely deterministic, all the call counts will be simple multiples of 100 (i.e., a function called once in each run will appear with a call count of 100).