Question

Compilers can have a profound impact on the performance of an application. Assume that for a program, compiler A results in a dynamic instruction count of 1.0E9 and has an execution time of 1.1 s, while compiler B results in a dynamic instruction count of 1.2E9 and an execution time of 1.5 s.

Find the average CPI for each program given that the processor has a clock cycle time of 1 ns.

Program A: ___________
Program B: ___________

Assume the compiled programs run on two different processors. If the execution times on the two processors are the same, how much faster is the clock of the processor running compiler A’s code versus the clock of the processor running compiler B’s code?

A new compiler is developed that uses only 6.0E8 instructions and has an average CPI of 1.1. What is the speedup of using this new compiler versus using compiler A or B on the original processor?

new compiler vs compiler A: ___________
new compiler vs compiler B: ___________

Answer 1

1)

Execution Time = Instruction Count x CPI x Clock Cycle Time

For Program A,

1.1 = 10^9 x CPI x 10^-9

CPI = 1.1

So for Program A, CPI = 1.1

For Program B,

1.5 = 1.2 x 10^9 x CPI x 10^-9

CPI = 1.25

So for Program A, CPI = 1.25

2)

It is given that execution times are same

But we know that

So Processor A is actually slower than B

3)

For new compiler vs compiler A:

So the new compiler is 1.66 times faster than Compiler A

For new compiler vs compiler B:

So the new compiler is 2.27 times faster than Compiler B