On chip photonic-nima afraz

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  • 1. On-Chip Photonic Nima Afraz Kazem farjami nejhad For the Advanced VLSI Course Term Paper Presentation February 2012 1
  • 2. Why?  To improve performance and energy in a future many-core processor, it is vital that the interconnect technology is optimized. 2
  • 3. Optical networks  silicon photonics is a promising new interconnect technology with lower power, higher bandwidth density, and shorter latencies. 3
  • 4. Contents  Introduction  Architecture Overview  Analysis and Comparison  Conclusion 4
  • 5. Introduction Low-latency high-bandwidth: How?  Packet-switched networks  Made of carefully engineered links  Represent a shared medium that is highly scalable  Provide enough bandwidth  But...  Communication infrastructure is the major power consumer  Power dissipation budget limit will be achieved 5
  • 6. Introduction Photonic Technology  Photonic interconnection networks  Low power dissipation independent of capacity  Ultra-high throughput  Minimal access latencies  Why less power?  Once a photonic path is established, the data is transmitted end to end without the need for repeating, regeneration and buffering 6
  • 7. Introduction Photonic Technology  Is photonic technology cheap enough?  Since 2006, high-speed optical communications directly between silicon die are possible at a price- performance point competitive with traditional electrical interconnects 7
  • 8. Contents  Introduction  Architecture Overview  Analysis and Comparison  Conclusion 8
  • 9. Architecture Overview Phonotonic NoC  Hybrid Approach  Photonic interconnection network  Transmits high-bandwidth messages  Electronic control network  Controls the photonic network with small control messages 9
  • 10. Architecture Overview Phonotonic NoC  Before transmitting a photonic message, an electronic control packet (path-setup packet)  is routed in the electronic network  acquires and sets up a photonic path for the message  Photonic message is transmitted without buffering once the path is acquired 10
  • 11. Architecture Overview Photonic NoC  Main advantage of photonic paths is bit-rate transparency  Photonic switches switch on or off once per message  Energy dissipation does not depend on the bit-rate  whereas  Traditional CMOS routers switch with every bit of transmitted data 11
  • 12. Architecture Overview Photonic NoC  Another advantage is low loss in optical waveguides  Power dissipated on a photonic link is completely independent of the transmission distance  No matter if 2 cores are 2mm or 2cm apart 12
  • 13. Architecture Overview Photonic NoC  2X2 photonic switching elements  Capable of switching messages in a sub nanosecond switching time  Switches are arranged as a 2D matrix and organized in groups of four  Each group is controlled by an electronic router to construct a 4X4 switch  Convenient for planar 2D topologies such as mesh and torus 13
  • 14. Architecture Overview Photonic NoC  Each node includes a network gateway to serve as a photonic network interface  Electronic/Optical (E/O) and Optical/Electronic (O/E) conversions  Clock synchronization and recovery  Serialization/deserialization  Wavelength division multiplexing is used at network gateways to provide larger data capacity  Optical equivalent of using parallel wires 14
  • 15. Architecture Overview Life of a Packet on Photonic NoC  Write operation from a processor in Node A to a memory in Node B 1. A path-setup packet is sent on the electronic control network  Includes information on the destination address of Node B and additional control information such as priority and flow id 2. Path-setup packet is routed in the electronic control network  Reserves the photonic switches along the path  At every router in the path, the next hop is decided according to the routing algorithm used 3. Path-setup packet reaches the destination  Photonic path is reserved  A fast light pulse is sent on the photonic path from Node B to Node A to indicate that the path is reserved 15
  • 16. Architecture Overview Life of a Packet on Photonic NoC 4. The photonic message starts from Node A follows path from switch to switch until it reaches Node B 5. Message transmission completed 6. Path-teardown packet is sent from Node B to Node A on the electronic control network to release the path 7. Photonic message is checked for errors and a small acknowledgement packet is sent from Node B to Node A on the electronic control network 16
  • 17. Contents  Introduction  Architecture Overview  Analysis and Comparison  Conclusion 17
  • 18. Analysis and Comparison Power Dissipation  Case Study Setup  16-node CMP where each processor requires  BWpeak = 1024 Gb/s  BWavg = 800 Gb/s  Traffic driven by the processors is assumed to be uniform  Both networks use a mesh topology and XY dimension order routing 18
  • 19. Analysis and Comparison Power Dissipation  Reference Electronic Network  4X4 mesh, where each router is integrated in one processor tile  PW=765W  Photonic Network  8X8 photonic mesh  256 photonic switching elements organized as 64 4X4 switches  PW=30W (96% less power dissipation) 19
  • 20. Contents  Introduction  Architecture Overview  Analysis and Comparison  Conclusion 20
  • 21. Conclusion  The advantages of photonic medium  High transmission bandwidth  Low power consumption  Recent (i.e. since 2006) advances make photonic technology practical for NoCs  Fabrication of silicon photonic devices  Integration of photonic devices in CMOS electronic circuits  Next generation of NoCs will possibly use photonic technology 21
  • 22. References  On the Design of a Photonic Network-on-Chip  Assaf Shacham, Keren Bergman, Luca P. Carloni  First International Symposium on Networks-on-Chip (NOCS'07), pp. 53-64, 2007  Photonic Networks-on-Chip: Opportunities and Challenges  Michele Petracca, Keren Bergman, Luca P. Carloni  IEEE International Symposium on Circuits and Systems 2008 (ISCAS 2008), pp. 2789-2792, May 2008  The Case for Low-Power Photonic Networks on Chip  Assaf Shacham, Keren Bergman, Luca P. Carloni  Proceedings of the 44th Annual Conference on Design Automation, pp. 132- 135, 2007  Maximizing GFLOPS-per-Watt: High-Bandwidth, Low Power Photonic On-Chip Networks  Shacham, K Bergman, LP Carloni  IBM P=ac2 Conference, October 2006 22