1. Computer Architecture Lecture 2 Instruction Set Principles

2. Amdahl’s Law The performance improvement to be gained from using faster mode of execution is limited by the fraction of the time the faster mode can be used

3. Amdahl’s Law: Law of Diminishing Returns

4. CPU performance Equations CPU Time = Instructions Program Clock Cycle Instruction Seconds Clock Cycle

5. Example: Frequency of FP operations = 25% Average CPI of FP operations = 4.0 Average CPI of other instructions = 1.33 Frequency of FPSQR = 2% CPI of FPSQR = 20 Assume CPI of FPSQR decreased to 2 OR the CPI of all FP operations to 2.5 Compare these two designs using the CPU performance equations

6. Example: Solution CPI for enhanced FPSQR CPI for enhanced FP operation

7. Example: Solution

8. Another Measure -- MIPS MIPS = Instruction Count Execution Time  10 6

9. Example: An Embedded Processor 120 MIPS for single processor. 80 MIPS for Processor –Co-Processor Combination (That is how they are measured for combined) I= Number of Integer Instructions F = Number of Floating Point Instructions (8 Million) Y = No. of Integer Instructions to Emulate one FP Instruction (50) W = Time for choice 1 (4 seconds) B = Time for Choice 2