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Computer Architecture: Performance and Design Principles, Lecture notes of Computer Architecture and Organization

Massachusetts Institute of Technology (MIT)Computer Architecture and Organization

An introduction to computer architecture, including topics such as technology, logic design, programming languages, operating systems, and hardware implementation. It also covers metrics of interest for computer architects, such as performance, cost, reliability, power, and area. Amdahl's Law and improving CPU performance through compiler optimizations, ISA, microarchitecture, and clock period. examples and benchmarking techniques for measuring performance.

Typology: Lecture notes

2021/2022

Uploaded on 05/11/2023

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Inf3 Computer Architecture - 2015-2016 1
Summary: Computer Architecture
What is Computer Architecture?
Computer Architecture:
• ISA
• Microarchitecture
• Hardware implementation
Operating System (OS)
Technology Logic design
Programming Languages
Compilers
Applications Users
Metrics of interest for computer architects
–Performance
–Cost
–Reliability
–Power
–Area
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Inf3 Computer Architecture - 2015-2016 (^1)

Summary: Computer Architecture

What is Computer Architecture?

Computer Architecture:

**- ISA

  • Microarchitecture
  • Hardware implementation Operating System (OS) Technology** (^) Logic design Programming Languages Compilers Applications Users

Metrics of interest for computer architects

  • Performance
  • Cost
  • Reliability
  • Power
  • Area

Inf3 Computer Architecture - 2015-2016 (^2)

Performance of Computer Architectures

▪ Metrics:

  • Execution time, response time: overall time for a given computation (e.g. full program execution, one transaction)
  • Latency: time to complete a given task (e.g. memory latency, I/O latency, instruction latency)
  • Bandwidth, throughput: rate of completion of tasks (e.g. memory bandwidth, transactions per second, MIPS, FLOPS)

▪ MHz, MIPS, FLOPS: must use with caution

▪ Benchmarking:

  • toy benchmarks, synthetic benchmarks, kernels, real programs,
  • Input sets
  • E.g. SPECint, SPECfp, EEMBC Coremark

Inf3 Computer Architecture - 2015-

Improving Performance: Principles of CA Design

▪ Take advantage of parallelism

  • System level: multiple processors, multiple disks
  • Processor level: pipelining, superscalar issue
  • Circuit level: carry-lookahead ALU

▪ Principle of locality

  • Spatial and Temporal Locality
  • 90% of program executing in 10% of code
  • E.g. Caches

▪ Focus on the common case

  • Amdahl’s law, CPU Performance equation
  • E.g. RISC design principle 4

Inf3 Computer Architecture - 2013-

Amdahl’s Law

5

Inf3 Computer Architecture - 2013-

Amdahl’s Law - Example

7

Inf3 Computer Architecture - 2015-

Factors that affect CPU performance

Instruction count (IC)

  • Compiler, ISA

Cycles per instruction (CPI)

  • ISA, microarchitecture

Clock time (1/f)

  • Microarchitecture, technology 8 What determines these factors?

Inf3 Computer Architecture - 2015-2016 (^10)

Examples

  • Branch instructions take 2 cycles, all other instructions take 1 cycle
  • CPU A uses extra compare instruction per branch
  • Clock frequency of CPU A is 1.25 times faster than CPU B
  • On A 20% of instructions are branches (thus other 20% are compare instructions) **Example: Find the CPU time CPIA = IC CPIbranch x ICbranch

IC CPIothers x ICothers = 2 x 0.2 + 1 x 0.8 = 1. CPIB = IC CPIbranch x ICbranch

IC CPIothers x ICothers = 2 x 0.25 + 1 x 0.75 = 1. CPU time** (^) B = ICB x CPIB x Clock time (^) B = 0.8 x ICA x 1.25 x (1.25 x Clock timeA) = 1.25 x ICA x Clock time (^) A CPU time (^) A = ICA x CPIA x Clock time (^) A = ICA x 1.2 x Clock time (^) A CPU A is faster!

Inf3 Computer Architecture - 2015-2016 (^11)

Improving CPU Performance

IC:
  • Compiler optimizations (constant folding, constant propagation)
  • ISA (More complex instructions) CPI:
  • Microarchitecture (Pipelining, Out-of-order execution, branch prediction)
  • Compiler (Instruction scheduling)
  • ISA (Simpler instructions) Clock period:
  • Hardware (Smaller transistors – Moore’s law)
  • ISA (Simple instructions that can be easily decoded)
  • Microarchitecture (Simple architecture)