At this level you need to start understanding details of the hardware and how actual execution differs from the model presented to the programmer. Here's the MIT course Computer System Architecture which gives an introduction to what you need to know.

https://ocw.mit.edu/courses/electrical-engineering-and-compu...

After that, I don't know, read some deep dives into a modern architecture and look up any terms you don't understand.

https://www.realworldtech.com/haswell-cpu/