Digital Design and Computer Architecture, ARM Edition

Example 7.5

Multicycle Processor CPI

The SPECINT2000 benchmark consists of approximately 25% loads, 10% stores, 13% branches, and 52% data-processing instructions.² Determine the average CPI for this benchmark.

Solution

The average CPI is the sum over each instruction of the CPI for that instruction multiplied by the fraction of the time that instruction is used. For this benchmark, average CPI=(0.13)(3)+(0.52+0.10)(4)+(0.25)(5)=4.12. This is better than the worst-case CPI of 5, which would be required if all instructions took the same time.

²Data from Patterson and Hennessy, Computer Organization and Design, 4th Edition, Morgan Kaufmann, 2011.

Recall that we designed the multicycle processor so that each cycle involved one ALU operation, ...