1. Design Space Exploration for NoC Topologies ECE757 6 th May 2009 By Amit Kumar, Kanchan Damle, Muhammad Shoaib Bin Altaf, Janaki K.M Jillella Course Instructor: Mikko Lipasti 6th May 20091Interconnect Evaluation

2. Outline Introduction Topologies Assessed Evaluation Methodology Results Constraints Conclusion 6th May 2009Interconnect Evaluation2

3. Outline Introduction Topologies Assessed Evaluation Methodology Results Constraints Conclusion 6th May 2009Interconnect Evaluation3

4. NoC Challenges –Performance requirement Low Latency Maximum Concurrent Communication –Tight energy and area constraints –Reliability requirements –Low cost 6th May 2009Interconnect Evaluation4

5. Outline Introduction Topologies Assessed Evaluation Methodology Results Constraints Conclusion 6th May 2009Interconnect Evaluation5

6. Topologies Assessed 6th May 2009Interconnect Evaluation6 RingCrossbarMeshTorusTreeButterfly Bi-directional RingFull Connected2D Clos k x n Array Hierarchical Ring (2 level) 3DFat TreeFlatten-c1 Hierarchical Ring (3 level) Flatten-c2

7. Ring 6th May 2009Interconnect Evaluation7 7 7 6 6 15 13 12 14 9 9 3 3 0 0 2 2 1 1 5 5 4 4 11 8 8 10

8. Crossbar 6th May 2009Interconnect Evaluation8

9. Mesh 6th May 2009Interconnect Evaluation9

10. Torus 6th May 2009Interconnect Evaluation10

11. Folded Clos 6th May 2009Interconnect Evaluation11

12. Fat Tree 6th May 2009Interconnect Evaluation12

13. Butterfly 6th May 2009Interconnect Evaluation13

14. Flattened Butterfly 6th May 2009Interconnect Evaluation14

15. Outline Introduction Topologies Assessed Evaluation Methodology Results Constraints Conclusion 6th May 2009Interconnect Evaluation15

16. Evaluation Methodology Minimal Dimension order routing Parameters –No of nodes(16,32) –Flit size(128,256) CMP protocols MOESI_CMP_token MSI_MOSI_CMP_ MOESI_CMP_directory Benchmark –Oltp, Apache, Jbb, Ocean Comparison –Latency, bandwidth, power, area. 6th May 2009Interconnect Evaluation16 Simics Ruby- Garnet Orion Latency, Through-put Area, Power

17. Outline Introduction Topologies Assessed Evaluation Methodology Results Constraints Conclusion 6th May 2009Interconnect Evaluation17

18. Results (1) Latency 6th May 2009Interconnect Evaluation18 **Latency in Cycles  2d torus is better than 2d mesh and 3d mesh.  Torus had enough path diversity.  Token protocol are equally good compared to directory protocols on Mesh/Torus/Butterfly

19. Results (1) Latency 6th May 2009Interconnect Evaluation19 **Latency in Cycles  HRing is not scalable compared to simple ring.  For small no of processor they add no of hops.  Token protocol works not well on rings.  Token cause congestion in the network.

20. Results (1) Latency 6th May 2009Interconnect Evaluation20 **Latency in Cycles  Butterfly is next competent to Mesh/Torus.  Flatten Butterfly are better then k-ary butterfly.  Increase in concentration for routers works very well.

21. Results (1) Latency 6th May 2009Interconnect Evaluation21 **Latency in Cycles  Token protocol does no perform well on tree.  Tokens overhead creates congestion in the network..

22. Results (5) Area Distribution 6th May 2009Interconnect Evaluation22

23. Results (4) Area 6th May 2009Interconnect Evaluation23 **Area in mm^2  2d Torus, clos,HRing are well scalable in terms of area.  Ring has less area compared to Mesh/Torus.

24. Results (3) Power Distribution 6th May 2009Interconnect Evaluation24  Crossbar consumes majority of power.

25. Results (2) Power 6th May 2009Interconnect Evaluation25 **Power in Watts  Token protocol takes more power due to high network traffic.  Ring has low power compared to Mesh/Torus.  Router area is decreased in ring.  Butterfly has lowest power consumption.  Refer to kanchan what is this binaray*

26. Results (6) Throughput 6th May 2009Interconnect Evaluation26 **Throughput in flits/cycle  Token cause congestion that leads to higher link utilization.

27. Results (6) Throughput 6th May 2009Interconnect Evaluation27 **Throughput in flits/cycle  HRing avoid congestion so token protocol have low link utilization.

28. Results (6) Throughput 6th May 2009Interconnect Evaluation28 **Throughput in flits/cycle  MSI gives less link utilization as it reduce the coherence traffic.  Increase in concentration leads to high link utilization in butterfly.

29. Results (6) Throughput 6th May 2009Interconnect Evaluation29 **Throughput in flits/cycle Refer to kanchan* why binary is giving high link uti* for MSI

30. Results (7) Latency 6th May 2009Interconnect Evaluation30 **Latency in Cycles  Higher latency compared to Oltp.  High cache-to-cache misses.  Token performs well.  Token is able to remove the cache to cache indirection latency which is the dominating factor..

31. Results (7) Throughput 6th May 2009Interconnect Evaluation31 **Throughput in flits/cycle  Token protocol highly utilize link(for tokens).  MSI protocol generates less traffic.  Ring /Tree has higher utilization.

32. Results (8) Power 6th May 2009Interconnect Evaluation32 **Power in Watts  Butterfly and concentrate butterfly consume less power.  Token consumes more power in Mesh/Torus.

33. Results (10) Scalability 6th May 2009Interconnect Evaluation33 **Latency in Cycles  Refer to janaki why 2d torus give low latency for 32p vs 16p*.  2D Torus/Butterfly are well scalable for all the protocol.  Token protocol doesn’t scale well compared to directory protocol.  MSI_MOSI protocol scalability is best.

34. Results (11) 2D v/s 3D 6th May 2009Interconnect Evaluation34 **Latency in Cycles  16% increase in performance.  17% increase in power.

35. Conclusion  Protocol  Token protocol can be an alternative for directory protocol(15% speedup).  Token protocol doesn’t work well for Oltp.  Token protocols are power hungry(link power).  Area  Ring /Torus scales well on area with increase in nodes.  Butterfly are next competent for area after Ring/Torus and scales very well.  Power-  Increase in concentration is always cost efficient as in butterfly.  Performance  Butterfly might be better choice given power/performance metric.  2D torus might be a better choice than 2D Mesh(16% speedup).  Scalability  Token protocol does not scale well as compared to directory protocol.  MSI_MOSI has higher scalability. 6th May 2009Interconnect Evaluation35

36. Thank You! Questions? 6th May 2009Interconnect Evaluation36