I've got no silver bullet for that. Recently I found a bunch of functions that were running slower on Windows. I eventually proved that their code had not chang

I've got no silver bullet for that. Recently I found a bunch of functions that were running slower on Windows. I eventually proved that their code had not changed and they were being run the same number of times as before. I had to use perf on Linux to prove that the i-cache miss rate was elevated due to changes elsewhere, making the identical code run slower. Having a good sense of how long something "should" take is certainly important, but investigating small performance regressions is always hard. That said, there are often a lot of big performance problems, and those are easier to find and often easier to understand, and more important to fix. Hey, maybe we shouldn't have a 50 MB global variable in each server instance -- whaddya think? Being a detective is good. Apply the scientific method, form hypotheses, test and reject them, rinse repeat. That's certainly way better than the off-applied "random guess based on Internet search" technique. Brendan's book is a good read.