Hybrid Optoelectric On-chip Interconnect Networks Yong-jin Kwon 1 Target Manycore System 2 On-chip network topology spectrum Increasing radix Increasing diameter Mesh CMesh ClosCrossbar 3 Related Works [Shacham07] [Petracca08] [Vantrease08] [Psota07] [Kirman06] [NOCS09] [Pan09] Mesh CMesh ClosCrossbar 4 Outline Technology Background Previous Studies and Motivation Performance Analysis Power Analysis Conclusion 5 Photonic technology photonic link 6 Silicon photonic link Coupler 7 Coupler loss = 1 dB Silicon photonic link Ring modulator 8 Modulator insertion loss = 0 1 dB Energy spent in E-O conversion = 25 90 fJ/bt (independent of link length) Silicon photonic link Waveguide 9 Waveguide loss = 0 5 dB/cm Silicon photonic link Ring filter, photodetector 10 Filter drop loss = 1.5 dB Photodetector loss = 0.1 dB Energy spent in O-E conversion = fJ/bt (independent of link length) Receiver sensitivity = -20 dBm 11 Silicon photonic link WDM Through ring loss = 1e- 4 1e-2 dB/ring Dense WDM (128 /wg, 10 Gbps/) improves bandwidth density (30x!!) 12 Silicon photonic link Energy cost E-O-E conversion cost fJ/bt (independent of length) Thermal tuning energy (increases with ring count) External laser power (dependent on losses in photonic devices) Silicon Photo 13 14 Electrical technology Design constraints 22 nm technology 500 nm pitch 5 GHz clock Design parameters Wire width Repeater size Repeater spacing FF Repeaters Repeater inserted pipelined wires 1.0 mm 2.5 mm 5.0 mm 7.5 mm 10.0 mm 15 Electrical technology Design constraints 22 nm technology 500 nm pitch 5 GHz clock Design parameters Wire width Repeater size Repeater spacing FF Repeaters Repeater inserted pipelined wires 1.0 mm 2.5 mm 5.0 mm 7.5 mm 10.0 mm 16 Electrical vs Optical links Energy cost Thermal tuning energy Transmitter- Receiver energy Elec: Electrical Opt-A: Optical-Aggressive Opt-C: Optical-Conservative Optical laser power not shown (dependent on the physical layout) Outline Technology Background Previous Studies and Motivation Proposed Design Performance and Power Analysis Conclusion 17 18 Clos Network 19 Photonic Clos for a 64-tile system 20 Power-Bandwidth tradeoff CMeshX2 Channel width = 128b PClos Channel width = 64b PClos Channel width = 128b Off-chip laser power = 3.3 W Comparable on-chip power for local traffic Problems and Motivations A mesh-like topology is highly optimized for local communication and hard to beat Solution: use a underlying mesh topology A fully photonic network has higher power numbers on low utilization Solution: make the photonic channels to be turned off at low utilization 21 What Do We Need? An electrical network which connects all-to-all even when the laser is turned off A photonic network which (when turned on) provides benefits to the base electrical mesh 22 Outline Technology Background Previous Studies and Motivation Proposed Design Performance and Power Analysis Conclusion 23 Concentrated Mesh with Photonic Express Channels 24 Express1Express2 Outline Technology Background Previous Studies and Motivation Proposed Design Performance and Power Analysis Conclusion 25 Performance 26 Power - Electrical 27 Photonic vs Electric Power Comparison 28 Outline Technology Background Previous Studies and Motivation Proposed Design Performance and Power Analysis Conclusion 29 Conclusion Maybe we do not need to shut down photonics on low utilization In order for photonics to be effective we need better devices There is no power advantage in using photonics if we cant get to aggressive We do win in bandwidth density but area is cheap 30 Acknowledgement Ajay Joshi Help in power calculations and images Chris Batten Brainstorming help 31 Thanks for your time 32
