Digital Design and Computer Architecture - Lecture 12: Microarchitecture 2

This post is a derivative of Digital Design and Computer Architecture Lecture by Prof. Onur Mutlu, used under CC BY-NC-SA 4.0.

You can watch this lecture on Youtube and see pdf.

I write this summary for personal learning purposes.

Agenda for Today

• Microarchitecture (principles & single-cycle uarch)
• Multi-cycle microarchitecture

Let’s Control The Single-Cycle MIPS Datapath

1. R-Type ALU
2. I-type ALU
3. LW
4. SW
5. Branch (Not Taken, Taken)
6. Jump

Evaluating the Single-Cycle Microarchitecture

How fast are my instructions?

• They can take one or more clock cycles to complete
• Cycles per Instruction = CPI

How much time is one clock cycle?

• one cycle requires = clock period
• 1/clock period = clock frequency

Our program executes in N(instructions) * CPI * (1/f = T) seconds

(Micro)architecture Design Principles

• Critical path design
  • Find and decrease the maximum combinational logic delay
  • Break a path into multiple cycles if it takes too long
• Bread and butter (common case) design
  • Spend time and resources on where it matters most
    • i.e., improve what the machine is really designed to do
  • Common case vs. uncommon case
• Balanced design
  • Balance instruction/data flow through hardware components
  • Design to eliminate bottlenecks: balance the hardware for the work

Aside: System Design Principles

• Yale Patt, “Requirements, Bottlenecks, and Good Fortune: Agents for Microprocessor Evolution,” Proc. of IEEE, 2001. (Levels of transformation, design point, etc)
• Mike Flynn, “Very High-Speed Computing Systems,” Proc. of IEEE, 1966. (Flynn’s Bottleneck à Balanced design)
• Gene M. Amdahl, “Validity of the single processor approach to achieving large scale computing capabilities,” AFIPS Conference, April 1967. (Amdahl’s Law à Common-case design)
• Butler W. Lampson, “Hints for Computer System Design,” ACM Operating Systems Review, 1983.
  • http://research.microsoft.com/pubs/68221/acrobat.pdf

A Key System Design Principle

• Keep it simple
• “Everything should be made as simple as possible, but no simpler.” - Albert Einstein
• Keep it low cost: “An engineer is a person who can do for a dime what any fool can do for a dollar.”

Multi-Cycle Microarchitectures

• Goal: Let each instruction take (close to) only as much time it really needs
• Idea
  • Determine clock cycle time independently of instruction processing time
• Each instruction takes as many clock cycles as it needs to take
  • Multiple state transitions per instruction
  • The states followed by each instruction is different

One Example Multi-Cycle Microarchitecture

Lecture, pdf p.81.