Performance Analysis

When comparing CPU performance by instructions executed per second (millions of instructions per second), what should be kept in mind?

  1. ADifferent instruction sets do different amounts of work per instruction, so more instructions per second does not guarantee a program finishes sooner
  2. BA CPU with a larger value is always faster on any program
  3. CThe value represents memory capacity
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Answer: A. Different instruction sets do different amounts of work per instruction, so more instructions per second does not guarantee a program finishes sooner

Instructions per second is an intuitive metric, but different instruction sets need different numbers of instructions for the same work. A CPU using many simple instructions tends to score higher without necessarily processing faster. Even within one instruction set, the value changes with each program's instruction mix. The most reliable comparison is to run the same program and measure the time.

  • A. Correct. What matters is time to complete the same work.
  • B. Results vary with instruction content and program.
  • C. It has nothing to do with memory capacity.
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More Performance Analysis questions

  1. How is speedup, which expresses a performance improvement, calculated?
  2. A part taking 50% of total time is made 4× faster. What is the overall speedup (Amdahl's law)?
  3. 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?
  4. Which lesson about how to approach performance improvement follows best from Amdahl's law?
  5. What idea does Gustafson's law express?