1. A computer has the following characteristics: • 3 GHz, 8 stage pipeline, inst
ID: 3760128 • Letter: 1
Question
1. A computer has the following characteristics: • 3 GHz, 8 stage pipeline, instruction buffers that negate instruction load penalties. • 25% of instructions are loads, 5% are stores. Branches are 20% and have an average branch penalty of .3 cycles. All other instructions are ideal (cpi 1) except for memory access delays. • 32Kb L1 cache, 500ps access, 8-way associative, write-through (via a buffer, that eliminates the penalty of writes to lower memory in all but 1/66 cases), not write- allocate, 1/21 miss rate for Data and a miss rate of 1/42 for Instructions • 1Mb L2 cache, 10ns access, 4-way associative, write-back, write-allocate, 20% miss rate, 10% dirty a. For the given instruction mix, what is the cpi? b. Assume the same CPU but no cache. What is the cpi? c. What is the speedup we get from cache?
Explanation / Answer
1)
25% of instructions are loads 25*.3 = 7.5
5% are stores 5*.3 = 1.5
Branches are 20% 20*.3 = 6
average branch penalty of .3 cycles
Total = 7.5+1.5+6 = 15/50 = 0.3 instruction/cycle
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