Ask HN: How to do performance optimizations like a pro?

I know that "premature optimization is the root of all evil". Still, I frequently find myself called upon to battle the monsters of poor application performance, so I might as well learn how to do it right. I'm interested in any advice you could give, especially related to desktop and server-side applications (I don't do much frontend, mobile or embedded).

Here's what I know:

- How to find my way around regular and statistical profilers for the languages I work most with.

- How to replace poor algorithms with better ones.

- How to go about finding performance hotspots by my gut and liberal amounts of timing statements.

Here's what I'd love to know:

- How to leverage system tools (Linux and Windows) to measure performance of an application in the context of its interactions with the hosting OS?

- What are the common/accepted practices of performance testing? In particuar, are there practices that make this exercise less painful/ad-hoc, and more systematic/streamlined?

- What are good strategies for including performance tests/safeguards in the usual CI/CD pipeline?

- Are there any good resources on application performance optimizations out there? Books, blogs, courses?

- What, beyond basic (regular and statistical) profilers should be an essential part of my toolbelt?

- Are there any interesting tools for analyzing and visualizing performance reports?

Thanks!