Exercise 1.15 Another pitfall cited in Section 1.8 is expecting to improve the overall performance of a computer by improving only one aspect of the computer. This might be true, but not always. Consider a computer running programs with CPU times shown in the following table.

FP instr. INT instr. L/S instr. Branch instr. Total time

a. 35 s 85 s 50 s 30 s 200 s

b. 50 s 80 s 50 s 30 s 210 s 1.15.1 [5] <1.8> By how much is the total time reduced if the time for FP operations is reduced by 20%?

1.15.2 [5] <1.8> By how much is the time for INT operations reduced if the total time is reduced by 20%?

1.15.3 [5] <1.8> Can the total time can be reduced by 20% by reducing only the time for branch instructions?

The following table shows the instruction type breakdown per processor of a given application executed in different numbers of processors.

# Processors FP instr. INT instr. L/S instr.

Branch Instr.

CPI

(FP)

CPI

(INT)

CPI

(L/S)

CPI

(Branch)

a. 1 560 × 106 2000 × 106 1280 × 106 256 × 106 1 1 4 2

b. 8 80 × 106 240 × 106 160 × 106 32 × 106 1 1 4 2 Assume that each processor has a 2 GHz clock rate.

1.15.4 [10] <1.8> By how much must we improve the CPI of FP instructions if we want the program to run two times faster?

1.15.5 [10] <1.8> By how much must we improve the CPI of L/S instructions if we want the program to run two times faster?

1.15.6 [5] <1.8> By how much is the execution time of the program improved if the CPI of INT and FP instructions is reduced by 40% and the CPI of L/S and branch is reduced by 30%?