Editing Speedup (section)

==Examples==
===Using execution times===
We are testing the effectiveness of a [[branch predictor]] on the execution of a program. First, we execute the program with the standard branch predictor on the processor, which yields an execution time of 2.25 seconds. Next, we execute the program with our modified (and hopefully improved) branch predictor on the same processor, which produces an execution time of 1.50 seconds. In both cases the execution workload is the same. Using our speedup formula, we know
:<math>S_\text{latency} = \frac{L_\text{old}}{L_\text{new}} = \frac{2.25~\mathrm{s}}{1.50~\mathrm{s}} = 1.5.</math>
Our new branch predictor has provided a 1.5x speedup over the original.

===Using cycles per instruction and instructions per cycle===
We can also measure speedup in cycles per instruction (CPI) which is a latency. First, we execute the program with the standard branch predictor, which yields a CPI of 3. Next, we execute the program with our modified branch predictor, which yields a CPI of 2. In both cases the execution workload is the same and both architectures are not pipelined nor parallel. Using the speedup formula gives
: <math>S_\text{latency} = \frac{L_\text{old}}{L_\text{new}} = \frac{3~\text{CPI}}{2~\text{CPI}} = 1.5.</math>

We can also measure speedup in instructions per cycle ([[Instructions per cycle|IPC]]), which is a throughput and the inverse of CPI. Using the speedup formula gives
: <math>S_\text{throughput} = \frac{Q_\text{new}}{Q_\text{old}} = \frac{0.5~\text{IPC}}{0.33~\text{IPC}} = 1.5.</math>

We achieve the same 1.5x speedup, though we measured different quantities.