Next, we add an L2 cache to P1 to presumably make up for its limited L1 cache ca

Question

Next, we add an L2 cache to P1 to presumably make up for its limited L1 cache capacity. Use the L1 cache capacities and hit times from the previous table when solving this next set of problems.

L2 miss rate

L2 hit time

1 MiB

95%

5.62ns

What is the AMAT for P1 with the addition of the L2 cache. Is the AMAT better or worse with the L2 cache?

Assuming a base CPI of 1.0 without any memory stalls, what is the total CPI for P1 with the addition of an L2 cache?

Which processor is faster, now that P1 has an L2 cache? If P1 is faster, what miss rate would P2 need in its L1 cache to match P1’s performance? If P2 is faster, what miss rate would P1 need in its L1 cache to match P2’s performance?

L2 miss rate

L2 hit time

1 MiB

95%

5.62ns

Explanation / Answer

Ans: AMAT = hit time L1 + miss rate(L1)*(hit time L2 + miss rate(L2)*miss penalty)

= 0.5+0.08*(5+0.75*70)

= 5.1

AMAT = 5.1 which is better.

Ans: New total CPI = 1+0.36*0.08*(5/0.5 + 0.75*70/0.5)

= 4.312

Ans: P1 has an L2 cache

->therefore 2/(4.312) = 0.464

- --> 1.25/(2.9) = 0.431

--> 0.464> 0.431

Therefore 'P1' is the faster. // thank you

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