[理工] [計組] 效能的問題

[da0910cc (da0910cc)]

1.(12%) Consider a program is executed on a computer. In the program 20% of
the instructions are branch instructions, and the other 30% are memory access
instructions. The computer has CPI of 2 for perfect cache and perfect branch
prediction. The penalty for each cache miss is 20 cycles, and for each branch
prediction miss is 1 cycle. If there are 1% of instruction cache miss, 10%
data cache miss, and 10% branch prediction miss, what is the actual CPI?
【解答】
 Actual CPI=ideal CPI+missrate*misspennalty=2+0.01*20+0.3*0.1*20+0.2*0.1*1

想請問,最後一個branch,為何不是0.2*0.1*(1+1)....miss時要額外多一個cycle,

然後instruction cache miss 是 (100%-20%-30%)*1%*20 ....  這樣對嗎?
                               ^^^^^^^^^^^^^ ^^ ^^
                               inst.占的比例*missrate*misspenalty

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推 ceo890710:因為只有算penalty的部分.只有1.不需要把原本的算進去
→ ceo890710:因為指令存取是每個指令都有所以是100%*1%*20
→ da0910cc:3Q!