If the profiler used is a sampling profiler (and it seems to be), then unlike with instrumentation-based profilers, it doesn't add any function call overhead.

If the profiler used is a sampling profiler (and it seems to be), then unlike with instrumentation-based profilers, it doesn't add any function call overhead. It just pauses the program every few ms and records what the call stack is at that point. While this makes the data noisier compared to instrumenting all calls, it also makes the data an unbiased approximation of how the program behaves when not being profiled. But sampling profilers do still tend to "basically just measure which function gets called most". They can tell a program spent a lot of time in a particular function, but they can't count how many times that function was called – so they can't determine whether it's a slow function, or a fast function that was called many times.