1. MS108 Computer System I Lecture 5 Pipeline Prof. Xiaoyao Liang 2015/3/27 1

2. Pipeline MIPS 2

3. 3Example In this example: –Sequential execution takes 4 * 90min = 6 hours –Pipelined execution takes 30+4*40+20 = 3.5 hours Bandwidth = loads/hour BW = 4/6 l/h w/o pipelining BW = 4/3.5 l/h w pipelining BW <= 1.5 l/h w pipelining, more total loads Pipelining helps bandwidth but not latency (90 min) Potential speedup = Number pipe stages ABCD 6 PM 789 TaskOrderTaskOrder Time 3040 20 Dave Patterson’s Laundry example: 4 people doing laundry wash (30 min) + dry (40 min) + fold (20 min) = 90 min Latency

4. 4 Pipeline Datapath

5. 5 Ideal Pipeline

6. Divide the Datapath 6

7. Timing Assumption 7

8. 5-Stage Pipeline 8

9. Resource Utilization 9

10. ALU Instructions 10

11. 11 IR and Control

12. 12 Control Generation

13. 13Hazards

14. 14 Data Hazard

15. 15Solutions

16. Feedback Killing 16

17. Stall 17

18. Stall and Pipeline Bubble 18

19. 19 Generate Stall

20. 20 Generate Stall

21. 21 Potential Stall Instructions

22. 22 Generate Stall

23. 23 Load/Store Hazard

24. 24 Load/Store Hazard

25. 25Jump

26. 26 Pipelined Jump

27. 27 Pipelined Jump

28. 28Branch

29. 29Branch

30. 30Branch

31. 31 New Stall

32. 32 Control Signals

33. 33 Branch Pipeline

34. 34 Reducing Branch Penalty

35. 35 Branch Delay Slot

36. 36Bypassing

37. 37 Adding Bypassing

38. 38 Fully Bypassing Datapath

39. 39 Limitation of Bypassing