[sshine]

If you want to "go low" in the operating system, you could write a Linux kernel module:

https://sysprog21.github.io/lkmpg/

https://blog.sourcerer.io/writing-a-simple-linux-kernel-modu...

If you want to "go low" in the way hardware works, you could try and write an interrupt handler on an embedded device.

If you want to "go low" in how optimizations work in application development, you could try and implement microbenchmarks and look at flamegraphs.

https://github.com/brendangregg/FlameGraph

https://bheisler.github.io/criterion.rs/book/index.html