Are Intel x86_64 processors not only pipelined architecture, but also superscalar?

问题

Are Intel x86_64 processors not only pipelined architecture, but also superscalar?

1. Pipelining - these two sequences execute in parallel (different stages of the same pipeline-unit in the same clock, for example ADD with 4 stages):

   • stage1 -> stage2 -> stage3 -> stage4 -> nothing
   • nothing -> stage1 -> stage2 -> stage3 -> stage4

2. Superscalar - these two sequences execute in parallel (two instructions can be launched to different pipeline-units in the same clock, for example ADD and MUL):

   • ADD(stage1) -> ADD(stage2) -> ADD(stage3)
   • MUL(stage1) -> MUL(stage2) -> MUL(stage3)

回答1:

Yes, contemporary Intel processors are both pipelined and superscalar.

It takes many nanoseconds to execute a single instruction. That includes fetching the instruction from the instruction memory, decoding the instruction, fetching the operands, performing any computations, fetching data from memory, and writing the results. For even basic performance it is important to break these into small steps and allow multiple instructions to be "in the pipeline" simultaneously.

Likewise, a processor pipeline consumes a lot of resources (area, power, design complexity, etc.). It is relatively very cheap to turn a 1-wide processor into a 2-wide, superscalar processor. The performance improvement is greater than the costs (although once you have a 4-wide processor, you will see diminishing returns going wider, and the costs grow exponentially).

Thus, you can expect any modern processor (except the absolutely smallest of the small) to be superscalar. Rule of thumb - if it's connected to a memory hierarchy, it will be superscalar. That's because the memory hierarchy consumes so much power and energy that you need a superscalar processor to keep it busy.

回答2:

Yes, it is. After some googling i found this

来源：https://stackoverflow.com/questions/28064856/are-intel-x86-64-processors-not-only-pipelined-architecture-but-also-superscala