Real World Performance

• Does clock speed suffice?
  • Assume Processor A runs at 3.2 GHz
  • Processor B runs at 1.8 GHz
  • Which is better?
  • This really depends on CPI and instruction count.
  • What if Processor B has a CPI of 1 and A has a CPI of 4?
  • What if the same program on A uses 10 times as many instructions?
• How about MIPS - Millions of instructions per second?
  • This is a bit better, but not really.
  • It can be a measure of the fastest to execute instruction
  • It is really just a measure of clock rate
• SPEC
  • Standard Performance Evaluation Corporation
  • Non-profit formed to establish performance standards.
  • Creates a set of vendor independent performance tests.
  • A set of standard programs are run, and the results are compared against a "standard"
  • Look at the Figure 1.20 on page 49.