How to improve CPI

• Recall:

Pipeline CPI = Ideal CPI + CPI contributed by stalls

• Ideal CPI =1 for single issue machine

  • Ideal CPI could be less than 1 if we have several pipes and we can issue multiple instructions in the same cycle, i.e., Instruction Level Parallelism (ILP)

• ILP will increase structural hazards

• ILP makes reduction in other stalls even more important

  • A “bubble” costs more than the loss of a single instruction issue

Next slide

Back to first slide

View graphic version