Consider 2 machines A and B running a workload that has the

Consider 2 machines (A and B) running a workload that has the following characteristics: 20% of the time, floating point instructions are being executed 80% of the lime, non floating point instructions arc being executed (assume no IO time) runs the workload in 60 seconds runs the workload in 50 seconds What is the speedup of machine B over machine A? Each machine has a proposed enhancement. Machine A will speedup all non floating point operations by a factor of 3. Machine B will speedup all floating point operations by a factor of 10. What is the Overall speedup of each machine with its enhancement? How long will it take each machine to run the workload with the enhancements? Machine A is a RISC processor and executed 3* 10**9 instructions lo execute the workload. Machine B is a CISC processor and executed 1 * 10* *9 instructions for the same Workload. The clock rate is 500 Megahertz (.5 gigahertz) for both machines. What is the CPI for the 2 machines after the enhancements are installed?

Solution

1) PerformanceA = 1 / Execution TimeA
PerformanceB = 1 / Execution TimeB

Speedup = n = PerformanceA/PerformanceB = Execution TimeB/Execution TimeA

Speedup = 60/50

=1.2 = 1+0.2

Therefore 20% of SpeedUp of Machine B over A.

2) Overall Speedup = 60 * 0.8*3/50*0.2*10

= 1.44

therefore overall Speedup after Enhancement is 44%

3) Time taken by each machine to run workload with enhancement are:

   Time taken by Machine A = 60*0.8*3 = 144 sec

   Time taken by Machine B = 50*.2*10 = 100 sec

4) cycles per Instruction, CPI = Clock Cycles / Number of instrucions

MAchine A:-

CPI = 3*500 * 10⁶ / 3*10⁹    (after enhancement of factor 3)

   = 500*10^-3

CPI = 0.5 clock cycles per instruction

Machine B:

CPI = 10 * 500 * 10⁶ / 1*10⁹ (after enhancement by factor 10)

= 5000 * 10^-3

CPI  = 5 clock cycles per instruction