cpu-architecture - 弗林瓶颈 - 最大加速 2

Question

根据 Flynn's Bottleneck，指令级并行 (ILP) 带来的加速最多可达 2。为什么会这样？

Answer 1

那个版本的弗林瓶颈起源于Detection and Parallel Execution of Independent Instructions作者根据经验得出结论，大多数程序的 ILP 小于 2。那是 1970 年的技术，是经验结论。您可以将其与 Fisher's Optimism 进行对比，后者表示存在大量 ILP，并提出跟踪调度和 VLIW 来利用它。

所以您问题的字面答案是因为那是他们当时在基本 block 中测量的值。

ILP 小于 2 的意思不再真正使用，因为超标量和更好的编译器已经超过了数字 2。因此，随着时间的推移，Flynn 的瓶颈 已经到来意思是You cannot retire more than you fetch这源于他早期的论文 Some Computer Organizations and Their Effectiveness .

The execution bandwidth of a system is usually referred to as being the maximum number of operations that can be performed per unit time by the execution area. Notice that due to bottlenecks in issuing instructions, for example, the execution bandwidth is usually substantially in excess of the maximum performance of a system.