Performance Analysis

You want to make an entire task 2× faster by speeding up only the part that takes 60% of the time. How many times faster must that part become?

  1. A2×
  2. B3.3×
  3. C6×
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Answer: C. 6×

Doubling overall speed requires the new time to be 0.5. The untouched 40% still takes 0.4, leaving 0.5 − 0.4 = 0.1 for the 60% part. Shrinking 0.6 to 0.1 requires a 6× speedup. As the unimprovable share approaches half the total, the required factor grows rapidly, and beyond 50% a 2× overall speedup becomes impossible.

  • A. Doubling only that part does not double the whole.
  • B. That computes 0.6 ÷ 0.3 but forgets the remaining 0.4.
  • C. Correct. 0.4 + 0.6 ÷ 6 = 0.5.
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More Performance Analysis questions

  1. Which lesson about how to approach performance improvement follows best from Amdahl's law?
  2. What idea does Gustafson's law express?
  3. What is the difference between strong scaling and weak scaling in evaluating parallel computing?
  4. What is the most appropriate approach when evaluating computer performance with benchmarks?
  5. Which describes a standard benchmark such as SPEC CPU?