I am using Callgrind in order to see how many times specific functions are called. However, I am also interested in the execution time.
I know the programs take much longer when running on Callgrind, since it has to take information. However, what I am surprised about is that how the time changes. In my case, I am running two different versions of the Fast Marching Method (FMM and Simplified FMM) on 2D and 3D grids. The results are as follow:
In 2D the ratio FMM/SFMM is not kept at all, but at least it is always >1 (it takes always longes for FMM than for SFMM). However, in 3D the effect of Callgrind is completely the opposite, the times are completely changed: SFMM takes shorter will callgrind but longer in regular execution.
The compilation I am using (-Ofast, -fno-finite-math-only) is the same all the time and the same binaries are being run in callgrind and regular running ./bin-name
The time measuring functions are those from std::chrono.
Therefore, the question is: as I am using the same binary in all cases, how is it possible that the same binary behaves so differently? Are the other data I am getting (function calls,% time cost, etc) reliable in this case? Callgrind-like results were expected when running the binaries with regular execution command.
EDIT: in the implemtation, the main change is that in FMM I am using the Boost Fibonacci heap and in the SFMM I am using a small modification with a Boost Priority Queue.
Thank you!
