Question

1. Suppose we have a 5-stage pipeline CPU and run the following instructions: or $tl, $t2, $t3 or $t2, $tl, $t4 or $tl, $tl, $t2 1.1. What dependencies are there in the code? 1.2. Suppose there is no forwarding. What hazard may happen? Draw the pipeline diagram and insert stall (nop) to prevent these hazard. 1.3. If the pipeline has full forwarding. Are there still hazard? If so, draw the pipeline diagram and insert stall (nop) to prevent the hazard. 2. For the following code lw $1, 40 ($6) beq $2,3, Labe12 add $1, $6, $4 beq $1,$2, Labell sw $2, 20 ($4) and $1, $1, $4 Labell: # taken Label2: # not taken Draw the pipeline diagram for running the code, assuming full forwarding and branching is done on the 3"d (EX) stage of the 5-stage pipeline. (No branch prediction) 3. Suppose when running a program, we have the following sequence of branch outcomes: (T branch taken, NT: branch not taken) T, T, T, NT, NT 3.1 What is the accuracy (i.e., the fraction of correct predictions) if we predict that branch is always taken or branch is always not taken? 3.2 What is the accuracy of a two-bit predictor for this sequence? Suppose the predictor is initialized to predict branch taken (the upper left state on Fig. 4.63 of the textbook). 3.3 If the sequence repeats forever, what is the accuracy of the two-bits predictor?

Answer 1

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