Consider the usage of critical word first and early restart on L2 cache misses. Assume a 1 MB L2 cache with 64 byte blocks and a refill path that is 16 bytes wide. Assume that the L2 can be written with 16 bytes every 4 processor cycles, the time to receive the first 16 byte block from the memory controller is 120 cycles, each additional 16 byte block from the memory requires 16 cycles, and data can be bypassed directly into the read port of the L2 cache. Ignore any cycles to transfer the miss request to the L2 cache and the requested data to the L1 cache.
a. How many cycles would it take to service an L2 caches miss with and without this technique (critical word first and early restart)?
b. Do you think critical word first and early restart would be more important for L1 caches or L2 caches, and what factors would contribute to their relative importance?