Consider two different processors P1 and P2 executing the same instruction set w

Question

Consider two different processors P1 and P2 executing the same instruction set with the clock rates and CPIs given in the following table. If the processors each execute a program in 15 seconds, find the number of cycles and the number of instructions for each processor. We are trying to reduce the program execution time by 20%, but this leads to an increase of 25% in the CPI. What clock rate should we have to get this time reduction for each processor? You may find this table of clock cycle times and clock rates useful:

Explanation / Answer

1) Here given processors clock rate means number of clock cycles per second and cycles per instruction(CPI) for each processor also given

for p1, it is 4GHZ means 4*10^9 cycles per second and CPI is 2

for p2, it is 4.5GHZ means (4.5)*10^9 cycles per second and CPI is 1.5

and each processor takes 15 seconds to complete. so

total number of cycles and total number of instructions are

for p1:

(15*4*10^9) cycles and total number of instructions are((15*4*10^9)/2)

  

for p2:

(15*(4.5)*10^9) cycles and total number of instructions are((15*(4.5)*10^9)/(1.5))

2)To reduce program execution time by 20%. so 20% of 15seconds is 3, by reducing this 3 seconds and to get execution time of 12 seconds and total number of cycles in execution will be constant in each processor.

for p1: 12*(clock rate) = 15*4*10^9

by solving this we get clock rate for p1 is 5GHZ to reduce 20%execution time

for p2: 12*(clock rate) = 15*(4.5)*10^9

by solving this we get clock rate for p2 is 5.625GHZ to reduce 20%execution time

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