[Ygg2]

Ok. I'll bite. How do you identify that a performance uplift of part of the code will kill the performance of overall app? Or won't have any observable effect?

I'm not saying you can't spot naive performance pitfalls. But how do you spot cache misses reading the code?

[IshKebab]

For example if someone uses a linked list where a vector would have worked. Vectors are much faster, partly due to better spatial locality.

[Ygg2]

Ok (that's a naive performance problem), and you speed that up, but now a shared resource is used mutably more often, leading to frequent locking and more overall pauses. How would you read that from your code?