Dynamic vs Static instruction count

Question

What is the difference between dynamic and static instruction count?

a. Derive an expression to calculate the user CPU time as a function of following parameters: the dynamic instruction count (N), clock cycle per instruction (CPI) and clock frequency (f)

b. Explain the reason for choosing ‘dynamic’ instruction count as a parameter in Question 3a instead of ‘static’ instruction count

Answer 1

The dynamic instruction count is the actual number of instructions executed by the CPU for a specific program execution, whereas the static instruction count is the number of instruction the program has.

We usually use dynamic instruction count as if for example you have a loop in your program then some instructions get executed more than once. Also, in the presence of branches, some instructions may not be executed at all.

Answer 2

Execution time (ET) = clock cycles per instruction(CPI) * number of instruction(IC) * cycle duration (CD).

Since a cycle frequency/rate (CR) is simply the inverse of cycle duration I.e cycles per second- and vice versa

ET= (CPI *IC)/CR