Computer Organization and Design--计组作业习题（5.5）

计算机组成原理

Class Problem 

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1.Assume the first branch is taken 50% of the time and the loop iterates 100 times, and forwarding for all data hazards.

add 1 2 3

beq 1 5 1

lw 6 4 1

add 3 4 5

beq 5 7 -5

2）.How many cycles does the code take assuming speculate and squash where all branches are predicted fall through

No hazard：5*100-50=450

Data hazards：50*1=50

Control hazards：100*3+100*3=600

Total：4+450+50+600 = 1104

3）.How many cycles does the code take assuming speculate and squash where backward branches are predicted taken and forward branches fall through?

No hazard：5*100-50=450

Data hazards：50*1=50

Control hazards：(100-50)*3+100*3=450

Total：4+450+50+450 =954

 

 

2.Assume the first branch has the pattern TTTN that repeats, and the loop is iterated 100 times

add 1 2 3

beq 1 5 1

lw 6 4 1

add 3 4 5

beq 5 7 -5

1）.How many cycles does the code take assuming detect and stall for control hazards?

No hazard：5*100-100*(3/4)=425

Data hazards：100*(1/4)*1=25

Control hazards：100*3+100*3=600

Total：4+425+25+600 =1054

2）.How many cycles does the code take assuming speculate and squash where backward branches are predicted taken and forward branches fall through?

No hazard：5*100-100*(3/4)=425

Data hazards：100*(1/4)*1=25

Control hazards：100*3+100*(1/4)=375

Total：4+ 425+25+375=829

3）.What if a 2-bit counter BTB is used to predict each branch, how many cycles does the code take?

No hazard：5*100-100*(3/4)=425

Data hazards：100*(1/4)*1=25

Control hazards：第一个beq，除了第一次TTTN时，有3次预测失败，此后每次TTTN只有1次失败，共计失败27次

              第二个beq，只有0和1两个状态预测失败，失败2次

              所以：(27+2)*3 = 87

Total：4+ 425+25+87=541