If you want to learn how to understand the performance of the whole system I can recommend Brendan Gregg's Systems Performance: Enterprise and the Cloud (https://www.brendangregg.com/blog/2020-07-15/systems-perform...). It is a good book that teaches a lot of basics and techniques and gives a good understanding of the impact different system components can have on performance.
I am so fascinated by how differently people interpreted this thread, really shows the diversity of computing and performance work. Here's a book about performance in the context of "enterprise and the cloud".
I've worked with performance optimizations for years, but never touched a network connection. Because for me it's all in the context of optimizing single player video games, which primarily leads to a focus on graphics programming and GPU performance.
"I am so fascinated by how differently people interpreted this thread, really shows the diversity of computing and performance work."
Well yeah, my first reaction to the question was: Optimize for what?
The question probably would have benefited from a bit more details about his job. Plattform, domain, etc.
I am also in the same boat as you, where I have 16 ms to do everything. So some of the general things we optimize for, also apply elsewhere, but many others not so much.
My main generic advice would be: things that happen only sometimes, can usually be slow, but things you need to do often ("hot spots") they need attention.
But of course this does not apply to a programm that checks for example whether the airbag of the car needs to fire, because some very rare condition was met. This code only runs very rarely - but if it does, there should be no garbage collector kicking in at that moment, no slow DB lookup, no waiting for a UI process to finish or alike (which should not have a connection anyway to the critical parts).
