Fundamentals of Quantitative Design and Analysis - Computer Architecture: A Quantitative Approach - page 53

We can compute the CPI for the enhanced FPSQR by subtracting the cycles
saved from the original CPI:
We can compute the CPI for the enhancement of all FP instructions the same
way or by summing the FP and non-FP CPIs. Using the later gives us:
Since the CPI of the overall FP enhancement is slightly lower, its performance
will be marginally beter. Speciically, the speedup for the overall FP enhance-
ment is
Happily, we obtained this same speedup using Amdahl's law on page 46.
It is often possible to measure the constituent parts of the processor performance equation.
This is a key advantage of using the processor performance equation versus Amdahl's law in
the previous example. In particular, it may be difficult to measure things such as the fraction
of execution time for which a set of instructions is responsible. In practice, this would prob-
ably be computed by summing the product of the instruction count and the CPI for each of the