Author here, kinda sorta. I should've been a bit more specific than that.
You can have a profile showing a function taking up 99% of the time, but when you dive into it, there's no clear bottleneck. But just because there's no bottleneck, that doesn't mean it's optimized; vice versa-a well-optimized program can have a bottleneck that's already been cycle-squeezed to hell and back.
What I wanted to say was that a spiky profile provides a clear path to optimizing a piece of code, whereas a flat profile usually means there are more fundamental issues (inefficient memory management, pointer chasing all over the place, convoluted object system, etc.).
What I wanted to say was that a spiky profile provides a clear path to optimizing a piece of code, whereas a flat profile usually means there are more fundamental issues (inefficient memory management, pointer chasing all over the place, convoluted object system, etc.).