Hybrid Optoelectric Onchip Interconnect Networks Yongjin Kwon 1
Hybrid Optoelectric On-chip Interconnect Networks Yong-jin Kwon 1
Target Manycore System 2
On-chip network topology spectrum Mesh Clos Crossbar Increasing diameter Increasing radix 3
Related Works Mesh [Shacham’ 07] [Petracca’ 08] CMesh Clos [NOCS’ 09] [Pan’ 09] Crossbar [Vantrease’ 08] [Psota’ 07] [Kirman’ 06] 4
Outline • • • Technology Background Previous Studies and Motivation Performance Analysis Power Analysis Conclusion 5
Photonic technology – photonic link 6
Silicon photonic link – Coupler loss = 1 d. B 7
Silicon photonic link – Ring modulator Energy spent in E-O conversion = 25 – 90 f. J/bt (independent of link length) Modulator insertion loss = 0 – 1 d. B 8
Silicon photonic link – Waveguide loss = 0 – 5 d. B/cm 9
Silicon photonic link – Ring filter, photodetector Energy spent in O-E conversion = 25 - 60 f. J/bt (independent of link length) Receiver sensitivity = -20 d. Bm Photodetector loss = 0. 1 d. B Filter drop loss = 1. 5 d. B 10
Silicon photonic link – WDM Through ring loss = 1 e 4 – 1 e-2 d. B/ring • Dense WDM (128 λ/wg, 10 Gbps/λ) improves bandwidth density (30 x!!) 11
Silicon photonic link – Energy cost • E-O-E conversion cost – 50 -150 f. J/bt (independent of length) • Thermal tuning energy (increases with ring count) • External laser power (dependent on losses in photonic devices) 12
Silicon Photo 13
Electrical technology Repeaters FF FF FF Repeater inserted pipelined wires • Design constraints – 22 nm technology – 500 nm pitch – 5 GHz clock • Design parameters – Wire width – Repeater size – Repeater spacing 14 10. 0 mm 7. 5 mm 5. 0 mm 2. 5 mm 1. 0 mm
Electrical technology Repeaters FF FF FF Repeater inserted pipelined wires • Design constraints – 22 nm technology – 500 nm pitch – 5 GHz clock • Design parameters – Wire width – Repeater size – Repeater spacing 15 10. 0 mm 7. 5 mm 5. 0 mm 2. 5 mm 1. 0 mm
Electrical vs Optical links – Energy cost Elec: Electrical Opt-A: Optical-Aggressive Opt-C: Optical-Conservative Optical laser power not shown (dependent on the physical layout) Thermal tuning energy Transmitter. Receiver energy 16
Outline • • • Technology Background Previous Studies and Motivation Proposed Design Performance and Power Analysis Conclusion 17
Clos Network 18
Photonic Clos for a 64 -tile system 19
Power-Bandwidth tradeoff Off-chip laser power = 3. 3 W Comparable on-chip power for local traffic CMesh. X 2 Channel width = 128 b 20 PClos Channel width = 64 b PClos Channel width = 128 b
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 Express 1 Express 2 24
Outline • • • Technology Background Previous Studies and Motivation Proposed Design Performance and Power Analysis Conclusion 25
Performance Latency (Cycles) 200 150 100 50 Latency (Cycles) 0 200 0 Latency (Cycles) CMesh 5 10 Express 1 15 20 5 10 Express 2 15 20 150 100 50 0 200 0 180 160 140 120 100 80 60 40 20 0 0 Uniform 5 Random 10 Paritition 2 Distributed 15 Bandwidth (kb/s) Partition 8 Colocated Partition 8 Distributed 20 26
Power - Electrical CMesh 150 Power (W) 40 100 50 20 0 5 10 Express 1 15 20 0 5 10 15 20 50 150 Power (W) Latency (Cycles) 30 10 0 200 0 100 50 0 200 0 5 180 160 140 120 100 80 60 40 20 0 0 5 Uniform Random 10 Express 2 Latency (Cycles) 50 15 10 Paritition 15 2 Distributed 20 Bandwidth (kb/s) Partition 8 Colocated Partition 8 Distributed 40 30 20 10 0 20 50 Power (W) Latency (Cycles) 200 40 30 20 10 0 27
Photonic vs Electric Power Comparison 50 Express 1 45 50 45 Power (W) 40 40 40 35 35 30 30 30 25 25 25 20 20 20 15 15 15 10 10 10 5 5 5 0 0 50 5 10 15 20 0 5 10 Conservative 45 35 0 15 0 20 0 5 10 15 20 Express 2 45 50 45 40 35 30 25 20 15 10 5 0 40 35 Power (W) 50 Aggressive 30 25 20 15 10 5 0 0 5 10 15 20 50 45 40 35 30 25 20 15 10 5 0 0 5 10 15 28 20
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 can’t 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
- Slides: 32