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.
gprofcan 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?
- 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).