Which is the most reliable profiling tool gprof or kcachegrind?

Question

Profiling some C++ number crunching code with both gprof and kcachegrind gives similar results for the functions that contribute most to the execution

Answer 1

gprof's timing data is statistical (read about it in details of profiling docs).

On the other hand, KCacheGrind uses valgrind which actually interprets all the code.

So KCacheGrind can be "more accurate" (at the expense of more overhead) if the CPU modeled by valgrind is close to your real CPU.

Which one to choose also depends on what type of overhead you can handle. In my experience, gprof adds less runtime overhead (execution time that is), but it is more intrusive (i.e. -pg adds code to each and every one of your functions). So depending on the situation, on or the other is more appropriate.

For "better" gprof data, run your code longer (and on as wide a range of test data you can). The more you have, the better the measurements will be statistically.