Suppose we have a system with 8-byte words and a cache with 32-byte blocks connected directly to memory. The cache has a hit time of 10 ns. The bus to memory is 8 bytes wide, requesting a word from memory takes 100 ns (total, aka round trip time), and memory bus transactions are serialized (not pipelined). The baseline cache requests each word from memory sequentially on a miss, and waits to respond to the CPU until miss repair is fully complete. Consider a workload with poor locality, with a cache hit rate of only 20%. Show your work. (a) What is the AAT speedup of early restart over baseline? Assume a uniform distribution of accesses to each word in a block (25% chance of each). This means that 25% of misses are for word 1 in a block, 25% for word 2, 25% for word 3, and 25% for word 4. (b) What is the AAT speedup over baseline of early restart if the distribution of accesses to each word in a block is 5%, 15%, 30%, and 50%, respectively? (c) What is the AAT speedup over baseline with critical word first with early restart?
Suppose we have a system with 8-byte words and a cache with 32-byte blocks connected directly to
memory. The cache has a hit time of 10 ns. The bus to memory is 8 bytes wide, requesting a word
from memory takes 100 ns (total, aka round trip time), and memory bus transactions are serialized (not
pipelined). The baseline cache requests each word from memory sequentially on a miss, and waits to
respond to the CPU until miss repair is fully complete. Consider a workload with poor locality, with a
cache hit rate of only 20%. Show your work.
(a) What is the AAT speedup of early restart over baseline? Assume a uniform distribution of accesses
to each word in a block (25% chance of each). This means that 25% of misses are for word 1 in a
block, 25% for word 2, 25% for word 3, and 25% for word 4.
(b) What is the AAT speedup over baseline of early restart if the distribution of accesses to each word
in a block is 5%, 15%, 30%, and 50%, respectively?
(c) What is the AAT speedup over baseline with critical word first with early restart?
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