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Lecture 10 | Memory Hierarchy

:material-circle-edit-outline: 约 278 个字 :material-clock-time-two-outline: 预计阅读时间 1 分钟

Orga_Ch5_V1.1(2).pdf

计算机组成2024-04-30第6-8节 (zju.edu.cn)

5.1 Concepts

前部分都没怎么看，PPT 1~18

主要是看各种概念，各种原理，以及性能比较

我们希望实现的是，在CPU看来，内存的速度和它一样快，大小无穷大

但是这是无法实现的

这部分可以看下前面CSSelf部分晶体管部分

5.2 Memory Hierarchy Introduction

Programs access a small proportion of their address space at any time

  • Temporal locality: Items accessed recently are likely to be accessed again soon
  • Spatial locality: Items near those accessed recently are likely to be accessed soon

Memory Hierarchy Levels

image-20240516191050658

  • Block (aka line): unit of copying

If accessed data is present in upper level

  • Hit: CPU access satisfied by upper level
    • Hit ratio: hits/accesses
    • Hit time: The time to access the upper level of the memory hierarchy, which includes the time needed to determine whether the access is a hit or a miss.

If accessed data is absent

  • Miss: CPU accesses the upper level and fails. Block copied from lower level
    • Time taken: miss penalty
      • miss penalty: The time to replace a block in the upper level with the corresponding block from the lower level, plus the time to deliver this block to the processor.
    • Miss ratio: misses/accesses = 1 – hit ratio

hit定义是，CPU读取层级最近的mem是否能直接读取到

image-20240516191631622