I will say I have worked on projects where sales and upper management were both saying the same thing: customers don't like that our product is slow(er than a c

I will say I have worked on projects where sales and upper management were both saying the same thing: customers don't like that our product is slow(er than a competitors), and the devs just shrug and say we've already done everything we can. In one case the most senior devs even came up charts to prove this was all they were going to get. Somehow I found 40%. Some of it was clever, a lot of it was paying closer attention to the numbers, but most of it was grunt work. Besides the mechanical sympathy, the other two main tools were 1) stubbornness, and 2) figuring out how to group changes along functional testing boundaries, so that you can justify making someone test a change that only improves perf by 1.2% because they're testing a raft of related changes that add up to more than 10%. Most code has orphaned performance improvements in 100 little places that all account for half of the runtime because nobody can ever justify going in and fixing them. And those can also make parallelism seem unpalatable due to Amdahl.