1. Power Issues in On-chip Interconnection Networks Mojtaba Amiri Nov. 5, 2009

2. 2 ECE692 2009

3. 3 – Performance, Reliability – Power Consumption

4. 4 ECE692 2009 PowerHerd: A distributed scheme for dynamic satisfying peak power constraints in interconnection networks Dynamic voltage scaling with links for power optimization of interconnection networks By L. Shang, L.-S. Peh, and N. K. Jha ECE, University of Princeton

5. By L. Shang, L.-S. Peh, and N. K. Jha Department of Electrical Engineering Princeton University

6. 6 ECE692 2009 Problem Peak-power constrains Solution PowerHerd – Distributed and run-time – Modified router

7. 7 ECE692 2009 – An Example

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9. 9 P LPB =P GPB /# Routers Estimate P LPB Predict P LPB Calculate Shared power Negotiation with neighbors and share power Update P LPB Throttle switch allocator Update routing decision

10. 10 ECE692 2009 Power dominators: – Input Buffer – Crossbar Switch – Link Based on Switching activity, Number, Coefficients from linear regression

11. 11 ECE692 2009 Orion error 2-3% Total 10%

12. 12 ECE692 2009 Leakage Power is about 10%. (Critique) Based on Switching activity, Number, Coefficients from linear regression

13. 13 ECE692 2009 W around 4 3 Hardware Simplification By shift and add

14. 14 ECE692 2009 T GPB /N

15. 15 ECE692 2009 1/2

16. 16 ECE692 2009 Near the local power budget Simple gating (Critique)

17. 17 ECE692 2009 Previous routing algorithms – Performance – Fault-tolerance This routing algorithm considers power consumption of neighbors – Low overhead

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19. 19 ECE692 2009 Global Power budget Global Power budget 136.3 W 27.3 W

20. 20 ECE692 2009 Global Power budget Global Power budget 136.3 W 53.3W

21. 21 ECE692 2009 P GPB = 136.3 W

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23. 23 ECE692 2009 PowerHerd – Distributed Scalable – Online (Dynamic) Efficient – Guarantee Peak-Power Constrain The Issue – Help other techniques

24. By L. Shang, L.-S. Peh, and N. K. Jha Department of Electrical Engineering Princeton University

25. 25 ECE692 2009 Power saving technique – Employs DVFS Links (the first attempt) How? Based on history of previous actions Performance penalty – 2.5 throughput – 15.2 average latency

26. 26 ECE692 2009 C= 5us n =.9 C= 5us n =.9 Characteristics of a DVFS link – Transition time (100 link clock cycles ) – Transition energy – Transition status – Transition step

27. 27 ECE692 2009 Link Utilization (LU) Congestion What is the Problem with this model?

28. 28 ECE692 2009 Congestion

29. 29 ECE692 2009 Congestion

30. 30 ECE692 2009 LU & BU together is enough DVFS based on two steps First Link Utilization Second congestion Simple Implementation

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34. 34 ECE692 2009 Task Duration Task Duration 1ms 0.1 us

35. 35 ECE692 2009 Appling DVFS to Interconnection networks History-based DVFS (LU, BU) Power saving HUGH! First study

36. 36 ECE692 2009 Consider static power 10% now is much more! Gate-level design for traffic throttling is not realistic. Completely Distributed; suggestion hybrid!

37. 37 ECE692 2009 There is no 100% guarantee to find the optimum for History-Based Policy This method works because the link is supposed to be power dominator! Inconsistent with first paper.

38. 38 ECE692 2009 PowerHerdDVFS Link TargetPeak Power ConstrainPower Consumption Performance PenaltyYes Power TechniquePower –aware routing, Dynamic power throttling DVFS Improvement100% guarantee6 times saving Inconsistent Assumptions (most power dominator) Input BuffersLinks