Question

Performance depends on several software and hardware components: the algorithm, programming language, compiler, instruction set architecture, and hardware architecture. Which specific performance term(s) (IC, CPI or CT) does each one of these components affects and how?

Answer 1

How the Performance is affected by several Software and Hardware components?

Before we look into how the performance of a program depends on the algorithm, the language, the compiler, the instruction set architecture as well as the actual hardware, we must first look into the Performance equation.

Please refer to the figure below:

Note:

IC  stands for Instruction Count.

CPI stands for Cycles per Instruction.

CT stands for Seconds per Cycle.

1. Compiler (Instruction Count and Cycles per Instruction affected)

As the compiler determines the translation of the source language instructions into computer instruction the efficiency of the compiler affects both the instruction count and the cycles per instruction. Compiler optimization can help reduce instruction count as well as improve CPI through a good selection of instruction combination as well as through the use of registers.

2. Algorithm (Instruction Count affected and Cycles per Instruction possibly affected)

The algorithm determines the number of source program instructions executed and hence the number of processor instructions executed. CPI may be affected due to the bias towards slower or faster instructions. Eg. a program will have a higher CPI if an algorithm uses more floating-point operations.

3. Programming Language (Instruction Count and Cycles per Instruction affected)

As statements in the language are translated to processor instructions, we are able to determine the instruction count. Due to various feature of a programming language, the CPI might also be affected. Eg. An objected oriented programming language with heavy support for data abstraction will require indirect calls, which will use higher-CPI instructions.

4. Instruction Set Architecture (Instruction Count, Seconds per Cycle and Cycles per Instruction affected)

The instruction set architecture affects all three aspects of CPU performance since it affects the cost in cycles per instruction, the overall clock rate of the processor, and the instructions needed for a function.

5. Hardware (Seconds per Cycle and Cycles per Instruction affected)

The hardware does not keep track of the value of executed programs hence neglecting the instruction count. However, the hardware determines the overall clock rate and cost of cycles per instruction.