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Express Cube Topologies for On-chip Interconnects Boris Grot J. Hestness, S. W. Keckler, O. Mutlu † The University of Texas at Austin † Carnegie Mellon University ‡ Part of this work was performed at Microsoft Research Feb 17, 2009HPCA ‘09
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The Era of Many-core UTCS2HPCA ‘09 Intel Larrabee 16+ cores Bidirectional ring interconnect UT TRIPS 2x16 exec tiles 16 NUCA tiles Multiple networks Intel Polaris 80 tiles 8x10 mesh Tilera Tile 64 cores 5 mesh networks
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Networks on a Chip (NOCs) On-chip advantages No pin constraints Rich wiring resources On-chip limitations 2D substrates limit implementable topologies Logic area constrains use of wiring resources Energy/power budget caps Focus Topologies for tomorrow’s many-core CMPs HPCA ‘093UTCS
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Outline Introduction Existing topologies Multidrop Express Channels (MECS) Evaluation Generalized Express Cubes Summary UTCS4HPCA '09
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UTCS5HPCA '09 2-D Mesh
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Pros Low design & layout complexity Simple, fast routers Cons Large diameter Energy & latency impact UTCS6HPCA '09 2-D Mesh
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Pros Multiple terminals attached to a router node Fast nearest-neighbor communication via the crossbar Hop count reduction proportional to concentration degree Cons Benefits limited by crossbar complexity UTCS7HPCA '09 Concentration (Balfour & Dally, ICS ‘06 )
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UTCS8HPCA '09 Concentration Side-effects Fewer channels Greater channel width
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UTCS9HPCA ‘09 Replication CMesh-X2 Benefits Restores bisection channel count Restores channel width Reduced crossbar complexity
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UTCS10HPCA '09 Flattened Butterfly (Kim et al., Micro ‘07) Objectives: Improve connectivity Exploit the wire budget
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UTCS11HPCA '09 Flattened Butterfly (Kim et al., Micro ‘07)
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UTCS12HPCA '09 Flattened Butterfly (Kim et al., Micro ‘07)
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UTCS13HPCA '09 Flattened Butterfly (Kim et al., Micro ‘07)
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UTCS14HPCA '09 Flattened Butterfly (Kim et al., Micro ‘07)
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Pros Excellent connectivity Low diameter: 2 hops Cons High channel count: k 2 /2 per row/column Low channel utilization Increased control (arbitration) complexity UTCS15HPCA '09 Flattened Butterfly (Kim et al., Micro ‘07)
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UTCS16HPCA '09 Multidrop Express Channels (MECS) Objectives: Connectivity More scalable channel count Better channel utilization
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UTCS17HPCA '09 Multidrop Express Channels (MECS)
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UTCS18HPCA '09 Multidrop Express Channels (MECS)
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UTCS19HPCA '09 Multidrop Express Channels (MECS)
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UTCS20HPCA '09 Multidrop Express Channels (MECS)
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UTCS21HPCA ‘09 Multidrop Express Channels (MECS)
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Pros One-to-many topology Low diameter: 2 hops k channels row/column Asymmetric Cons Asymmetric Increased control (arbitration) complexity UTCS22HPCA ‘09 Multidrop Express Channels (MECS)
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Analytical Comparison UTCS23HPCA '09 CMeshFBflyMECS Network Size 642566425664256 Radix (conctr’d) 484848 Diameter 6142222 Channel count 2283248 Channel width 576115214472288 Router inputs 446146 Router outputs 4461444
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Experimental Methodology TopologiesMesh, CMesh, CMesh-X2, FBFly, MECS, MECS-X2 Network sizes64 & 256 terminals RoutingDOR, adaptive Messages64 & 576 bits Synthetic trafficUniform random, bit complement, transpose, self-similar PARSEC benchmarks Blackscholes, Bodytrack, Canneal, Ferret, Fluidanimate, Freqmine, Vip, x264 Full-system configM5 simulator, Alpha ISA, 64 OOO cores Energy evaluationOrion + CACTI 6 UTCS24HPCA '09
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UTCS25HPCA '09 64 nodes: Uniform Random
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UTCS26HPCA '09 256 nodes: Uniform Random
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UTCS27HPCA '09 Energy (100K pkts, Uniform Random)
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UTCS28HPCA '09 64 Nodes: PARSEC
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Generalized Express Cubes Low-dimensional k-ary n-cube n = {1,2} Good fit for planar silicon Express channels Improve connectivity MECS for better wire utilization Multiple networks Improve throughput Reduce crossbar area & energy overhead Hierarchical scaling UTCS29HPCA '09
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Partitioning: a GEC Example UTCS30HPCA '09 MECS MECS-X2 Flattened Butterfly Partitioned MECS
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Summary MECS A novel one-to-many topology Good fit for planar substrates Excellent connectivity Effective wire utilization Generalized Express Cubes Framework & taxonomy for NOC topologies Extension of the k-ary n-cube model Useful for understanding and exploring on-chip interconnect options Future: expand & formalize UTCS31HPCA '09
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Summary MECS A novel one-to-many topology Good fit for planar substrates Excellent connectivity Effective wire utilization Generalized Express Cubes Framework & taxonomy for NOC topologies Extension of the k-ary n-cube model Useful for understanding and exploring on-chip interconnect options Future: expand & formalize UTCS32HPCA '09
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UTCS33HPCA '09
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