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CPU流水线、多发射、超标量、CPU微码

这些术语，时长碰到，有必要梳理一下。

zhihu 关于CPU流水线 多发射 超标量 CPU微码 之间 的关系和原理?

A

作者：Sinaean Dean 链接：https://www.zhihu.com/question/66374524/answer/243527000 来源：知乎 著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。

流水线是指一条指令的执行被切分成多个阶段，交由不同的有独立功能的逻辑部件去依次执行。就好比一个人也可以做一道菜，你也可以把做菜分为洗菜、切菜、炒菜三道工序，交给三个人依次执行。

多发射就是说你有多条流水线，这样你原来可以交给CPU一条指令，现在可以同时交给他两条或是三条指令。

超标量是说你的CPU核心中有两个或更多的ALU，甚至FPU用来做计算。在没有多发射的情况下超标量也是可以用的，比如说一个ALU在执行一个多时钟周期的任务时，可以把下一条指令交给令一个ALU。这就好比你有你的菜每样菜炒出来所需时间不一样，有的块有的慢，但洗菜和切菜的速度是一样的，那有时可能配两个炒菜的师傅更好一下。

nyu.edu Lecture 17: Multiple Issue: SIMD, EPIC, and superscalar

分别介绍

wikipedia Superscalar processor

A superscalar processor is a CPU that implements a form of parallelism called instruction-level parallelism within a single processor.

NOTE: 单个 processor 内的 的并行

wikipedia Instruction pipelining

In computer science, instruction pipelining is a technique for implementing instruction-level parallelism within a single processor. Pipelining attempts to keep every part of the processor busy with some instruction by dividing incoming instructions into a series of sequential steps (the eponymous "pipeline") performed by different processor units with different parts of instructions processed in parallel.

NOTE:

1、这一段读完后，就觉得它和前面的Superscalar processor说的是同一个意思

wikipedia Wide-issue

A wide-issue architecture is a computer processor that issues more than one instruction per clock cycle.

NOTE:

1、一个时钟周期内发射多条指令

2、这应该是multiple issue

umd.edu Multiple Issue Processors I

NOTE:

1、介绍地比较详细

Types of Multiple Issue Processors: There are basically two variations in multiple issue processors – Superscalar processors and VLIW (Very Long Instruction Word) processors. There are two types of superscalar processors that issue varying numbers of instructions per clock. They are

  • statically scheduled superscalars that use in-order execution
  • dynamically scheduled superscalars that use out-of-order execution

Superscalar vs Instruction pipelining

在 Superscalar processor 中有这样的介绍:

While a superscalar CPU is typically also pipelined, superscalar and pipelining execution are considered different performance enhancement techniques. The former executes multiple instructions in parallel by using multiple execution units, whereas the latter executes multiple instructions in the same execution unit in parallel by dividing the execution unit into different phases.

1、Instruction pipelining 是 使用多个 "execution units"

2、Superscalar 是 每个 "execution units" 内部将instruction分为多个阶段，然后并行执行

关于此，在 zhihu 如何理解 C++11 的六种 memory order？ # A 中，有这样的总结:

简单来说，你可以理解当代CPU不仅是多核心，而且每个核心还是多任务（多指令）并行的。计算机课本上的那种一个时钟一条指令的，早就是老黄历了 （当然，宏观来看基本原理并没有改变）