Designing Nanophotonic Interconnection Networks

Transcription

1 Designing Nanophotonic Interconnection Networks Christopher Batten Computer Systems Laboratory Cornell University Workshop on the Interaction between Nanophotonic Devices and Systems December 2010

2 Cornell CSL Christopher Batten 2 / 31

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4 Based on experiences designing nanophotonic interconnection networks and surveying the literature, can we begin to identify common design patterns and guidelines? Cornell CSL Christopher Batten 4 / 31

5 Designing Nanophotonic Interconnection Networks Motivation Architectural-Level Design Microarchitectural-Level Design Physical-Level Design Design Guidelines Cornell CSL Christopher Batten 5 / 31

6 Architectural-Level Design Select logical topology which consists of input and output terminals interconnected by buses, routers, and channels Use topology diagram to capture design decisions Determine bus/channel bandwidths based on app demands Preliminary exploration of routing algorithms First-order analysis of various options to narrow design space Design electrical baseline network Cornell CSL Christopher Batten 6 / 31

7 Logical Network Topologies Cornell CSL Christopher Batten 7 / 31

8 Logical Network Topologies: Bus Input terminals globally arbitrate for single shared medium Benefits: Simple, single stage, serialize messages, broadcast Challenges: Global arbitration and data transfer Cornell CSL Christopher Batten 8 / 31

9 Logical Network Topologies: Crossbar Many parallel buses, one per terminal Benefits: Single stage, high throughput Challenges: Global arbitration and data transfer Cornell CSL Christopher Batten 9 / 31

10 Logical Network Topologies: Butterfly Multiple-stages arranged in butterfly pattern Benefits: Distributed routing, arbitration, flow-control Challenges: Multiple stages of switching, global channels Cornell CSL Christopher Batten 10 / 31

11 Logical Network Topologies: Torus Multiple-stages arranged in grid pattern possibly with wrap-around Benefits: Small localized routers, short channels (for low-dim) Challenges: Many stages of switching (for low-dim) Cornell CSL Christopher Batten 11 / 31

12 Example Architectural-Level Analysis Buses & Channels Routers Latency Topology N C N BC b C N BC b C N R radix H R T R T C T S T 0 Crossbar , n/a 4 14 Butterfly 8-ary 2-stage , Clos (8,8,8) , Torus 8-ary 2-dim , Mesh 8-ary 2-dim , CMesh 4-ary 2-dim , Cornell CSL Christopher Batten 12 / 31

13 Categorizing Previous Proposals Cornell CSL Christopher Batten 13 / 31

14 Microarchitectural-Level Design Choose which buses, routers, and channels to implement electrically and which to implement optically Use nanophotonic schematic to capture design decisions Decide where to use transmitters, receivers, active filters Decide arbitration for wavelengths, manage electrical buffering Finalize routing algorithm Ignore wavelength to waveguide mapping and waveguide layout Cornell CSL Christopher Batten 14 / 31

15 Schematic and Layout Symbols Cornell CSL Christopher Batten 15 / 31

16 Bus Microarchitectural Design Patterns Cornell CSL Christopher Batten 16 / 31

17 Crossbar Microarchitectural Design Patterns Cornell CSL Christopher Batten 17 / 31

18 Butterfly Microarchitectural Design Patterns Cornell CSL Christopher Batten 18 / 31

19 Torus Microarchitectural Design Patterns Cornell CSL Christopher Batten 19 / 31

20 Categorizing Previous Proposals Cornell CSL Christopher Batten 20 / 31

21 Physical-Level Design Map microarchitectural design to physical substrate Use a nanophotonic abstract layout diagram to capture design decisions Decide how to assign wavelengths to waveguides and fibers Decide how to layout waveguides and organize fibers Decide where to place nanophotonic devices along waveguides Cornell CSL Christopher Batten 21 / 31

22 Bus Physical Design Patterns Cornell CSL Christopher Batten 22 / 31

23 Crossbar Physical Design Patterns Cornell CSL Christopher Batten 23 / 31

24 Point-to-Point Channels Physical Design Patterns Cornell CSL Christopher Batten 24 / 31

25 Abstract Physical Layouts for Crossbar Cornell CSL Christopher Batten 25 / 31

26 Abstract Physical Layouts for Butterfly Cornell CSL Christopher Batten 26 / 31

27 Example Physical-Level Analysis Cornell CSL Christopher Batten 27 / 31

28 Example Network Simulation Results Cornell CSL Christopher Batten 28 / 31

29 Design Guidelines 1. Clearly specify the logical topology easy to confuse passively WDM-routed wavelengths with true network routing, helps position design relative to other proposals 2. Iterate through three design levels many mappings at each level, iterative approach avoids over-constraining the design space 3. Use aggressive electrical baseline is a low-dimensional mesh the best electrical comparison? are simple repeated wires really the best we can do? Cornell CSL Christopher Batten 29 / 31

30 Design Guidelines 4. Broad range of device parameters emerging technology means a single set of parameters is probably meaningless, sensitivity studies are essential 5. Consider fixed-power overheads only studying high-utilization workloads hides the significant impact of fixed transceiver circuit power, laser power, and thermal tuning power 6. Motivate network complexity if we should seek the simplest network architecture (and the simplest devices) that achieves our application requirements Cornell CSL Christopher Batten 30 / 31

31 Design Guidelines 1. Clearly specify the logical topology 2. Iterate through three design levels 3. Use aggressive electrical baseline 4. Broad range of device parameters 5. Consider fixed-power overheads 6. Motivate network complexity Cornell CSL Christopher Batten 31 / 31