Assume a multilevel cahe The L1 cache has a missrate of 8 Th

Assume a multi-level cahe. The L1 cache has a miss-rate of 8%. There is miss penalty of 12 cycles for reaching the L2 cache. The L2 cache has a miss rate of 5%. There is a 100 cycle miss penalty for reaching main memory. What is the average miss penalty for this cache?

Solution

L1 cache miss rate –> 8%
So, L1 hit rate –> 100 – 8 = 92%
To reach L2, miss penalty –> 12 cycles

L2 cache miss rate –> 5%
So, L2 hit rate -> 100 - 5 = 90%
To reach main memory, miss penalty –> 100 cycles
Ave. miss penalty of L2 = ?

Ave. Miss Penalty = L1 hit time * L1 hit rate + (L2 hit time * L2 hit rate + (L2 miss penalty * (1 - L2 hit rate) ))* L1 miss rate
       = 1 * 0.92+(12 * 0.9 + 100 * (1 - 0.9) * 0.08)
       = 0.92+(10.8+10)*0.08
= 0.92+1.664
= 2.584 cycles