CS251 - Computer Organization and Design - Spring 2008

Lecture 2 - Performance


Practical Details

  1. Course web pages
  2. Excessive collaboration

    Good rule of thumb: talk together but write independently

    Penalties are severe

  3. Read chapter 1
  4. Read sections 4.1 to 4.3; skim sections 4.4 to 4.6

Performance of Computer Systems

In the box on page 271, the authors write, `Execution time is the only valid ... measure of performance.'

This is not true!!

  1. real-time systems
  2. low power systems
  3. portable systems
  4. robust systems
  5. systems with user interfaces
  6. not to mention `entertaining systems' or `beautiful systems' or `systems that make you feel cool'.

Exercise for the reader. Write an essay on the social distortions that make it possible for the authors to write what they did, and presumably, believe, it.

So, how do we measure performance?

  1. Define an objective function.
  2. Measure the objective function in different system configurations

Execution time is commonly used as a proxy for other measures.

What affects execution time?

Features of the computer

  1. clock speed
  2. instruction set
  3. compiler efficiency
  4. memory speed
  5. I/O bandwidth

Features of the workload

  1. instruction mix
  2. computation versus memory versus I/O
  3. data locality

Possible computer solutions

Benchmarks

Collections of code to be executed, standard sets of problems to solve.


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