It’s also a big factor of “the fastest code is deleted code”. Someone sneaks in a loop or a second call to a function and disrupts the code flow and you can see

It’s also a big factor of “the fastest code is deleted code”. Someone sneaks in a loop or a second call to a function and disrupts the code flow and you can see some really weird shit. One of my first big counter examples to standard “low hanging fruit” philosophy was a profiler telling me a function was called 2x as often as the sequence diagram implied and occupying 10% of the overall cpu time for the operation. So I removed half of the calls by inverting a couple of calls to expose the data, which should have been a 5% gain (0.1 / 2). Total time reduction: more than 20%. Couple jobs later I managed a 10x improvement on one page transition from a similar change with an intersection test between two lists. Part of that was algorithmic but most was memory pressure. Remember if microbenchmarks lie, a profiler is just an inversion of the benchmark idea. Two sides of the same coin.