Instruction Scheduling

Question 1

What is instruction scheduling?

Answer 1

how the processor does register renaming and out-of-order execution

Question 2

What are the differences between Tomasulo’s Algorithm and modern processors?

Answer 2

• Only handles floating point instructions (now: all instructions)
• Looks ahead at a fewer number of instructions (now: 100s)
• Hardware didn’t directly support exception handling

Question 3

What are the steps in Tomasulo’s Algorithm?

Answer 3

1. instruction queue - fetch unit pushes instructions into the instruction queue
2. Issue - instruction is dequeued and sent to a reservation station, where it waits to be executed
3. Dispatch - Instruction dequeued from reservation station and sent to an ALU to be executed
4. Write result / broadcast - Instruction has been executed and we broadcast the results back to the instruction queue, registers, and reservation stations so that their values can be updated

Question 4

How does Tomasulo’s algorithm handle load / store instructions?

Answer 4

Just do them in order (memory locations can also have data dependencies)