Lets assume a computer with L2 cache that has a 128byte cach

Let’s assume a computer with L2 cache that has a 128-byte cache block. It takes 10 clock cycles to transfer the first 8 bytes to L1, and then 1 clock cycle per 8 bytes to transfer the rest of the block. Compare the miss penalty times with and without Critical Word First?

Solution

Given

clock cycles to transfer the first 8 bytes to L1 = 10

With Critical word first:

Average miss penalty = Miss Penalty of critical word + Miss penalty of the remaining words of the block

= 10 x 1 + (8-1) x 1 = 10+ 7 = 17 clock cycles

Without critical word first (it requires block load):

Average Miss Penalty = [Miss Penalty of first word + miss penalty of the remaining words of the block] + clock cycles to issue the load

= 10 x 1 + (8-1) x 1 + 8/2 = 17 + 4= 21 clock cycles

2 issues/cycle so 4cycles for 8 issues