To write highest performance assembly code you need to understand more than the instruction set. You need to understand about cache hierarchy and how cache line

To write highest performance assembly code you need to understand more than the instruction set. You need to understand about cache hierarchy and how cache lines are filled, about microcode and how to fill the pipeline, including how to exploit hyperthreads, what the consequence of different workloads is on boost speeds, how the vectorized instructions map to hardware and when the trade-off is worth it, etc... Not to mention that you really also need to be a GPGPU expert so you can trade off work to the graphics hardware when necessary. One can write assembly while knowing only a fraction of that stuff, but the compiler will probably outperform that kind of assembly, so there is little point aside from the fun of it.