Pipelining

Question 1

What are the 3 kinds of pipeline hazards?

Answer 1

1. Structural
2. Data
3. Control

Question 2

Explain structural hazards and give 2 solutions.

Answer 2

Simultaneous use of a hardware resource

1. Stall the pipeline
2. Use separate memory (Instruction/Data)

Question 3

What is RAW? (Data Dependency)

Answer 3

Read-After-Write.

• Occurs when a later instruction reads from the destination register in an earlier instruction.
  add $2, $1, $3
  add $4, $2, $1

Solution:
Using data forwarding.

Question 4

What is Control Dependency? What are the 3 solutions?

Answer 4

An instruction j that is control dependent on i if i controls whether or not j executes. (typically a branch instruction)

beq $3, $5, label
add $1, $2, $4

Solutions:

1. Early branching (decision made in stage 2)
2. Branch prediction (Fetches the next instruction)
3. Delayed branching