Problem : A. Assume the miss rate of an instruction cache is 4% and the miss rat

Question

Problem :

A. Assume the miss rate of an instruction cache is 4% and the miss rate of the data cache is 10%. If a processor has a CPI of 2 without any memory stalls and the miss penalty is 100 cycles for all misses, determine how much faster a processor would run with a perfect cache that never missed. Assume the frequency of all loads and stores is 40%.

B. Find the average memory access time(AMAT) for a processor with a 1 ns clock cycle time, a miss penalty of 40 clock cycles, instruction miss rate of 10%, and a cache access time (including hit detection) of 1 clock cycle. Assume that the read and write miss penalties are the same and ignore other write stalls.

Explanation / Answer

A. Let the instruction count be I

Instruction cache stalls = I * 0.02 * 100 = 2I

Data cache stalls = I * 0.40 * 0.10 * 100 = 4I = Total memory stalls = 6 * I

CPI with perfect memory = 2.0

CPI with memory stalls = 7

pERFECT MEMORY PERFORMANCE IS 7/2 OR 3.5

b. aVERAGE MEMORY ACCESS TIME (amat)

= Hit time + Miss rate * Miss penality(ns or clocks)

Miss rate = 10%

miss penality = 40 clock cycles

Hit detection = 1 clock cycle.

1 + 0.01 * 100 = 2ns

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