CPU with CPI execution is 1.1 with clock rate = 2GHz (0.5ns). Hit ratio of the f

Question

CPU with CPI execution is 1.1 with clock rate = 2GHz (0.5ns). Hit ratio of the first cache level L1 is 99% and its access time is 4 ns (8 cycles). Hit rate of L2 is 99.4% and its access time is 8ns (16 cycles). Hit rate of L3 is 99.8% and its access time is 10ns (20 cycles). Main memory access time = 100ns (200 cycles).

Calculate the effictive CPI in the following cases:

a. with just L1

b. with the L1 and L2 only

c. with L1, L2, L3 and the memory

d. Calculate the the CPU time to execute an instruction. (for part c)

Explanation / Answer

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Find the CPI for the following system:

Cpu with CPI execution is 1.1 with clock rate = 2GHz (0.5ns). Each instruction requires 2 memory accesses. Hit ratio of the first cache level L1 is 99%. Hit rate of L2 is 99.5% and its access time is 8ns (16 cycles). Main memory access time = 100ns (200 cycles).

a. if we have L2 only ( no miss in L2 in this case)

b. if we have L2 and the memory (no miss in the memory)

c. in each case, calculate the CPU time to execute an instruction

Answer

a) no miss in L2

Assume no of Instructions=1
The no of memory miss cycles=1*1%*100=1*0.01*100=1
Data miss cycles=1*100=100
Total Number of memory stall cycles=16+1+100=117
CPI=1.1
CPU Time=1.1/117=9.40-E3

b) no miss in the memory

Assume no of Instructions=1
The no of memory miss cycles=1*1%*100=1*0.01*100=1
Data miss cycles=1*0.5%*1%*100=1*0.005*0.01*100=0.005
Total Number of memory stall cycles=16+1+0.05=17.05
CPI=1.1
CPU Time=1.1/17.05=0.0645

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