A DeadlockFree Routing Scheme for Interconnection Networks with Irregular Topologies

1
A Deadlock-Free Routing Schemefor
Interconnection Networks with Irregular
Topologies

• Hsin-Chou Chi
• Dept. of Computer Science Information
  Engineering
• National Dong Hwa University

2
Outline
1. Routing for Irregular Interconnection
Networks 2. Previous Work 3. A
Tree-Based Routing Architecture for Irregular
Networks 4. Performance Evaluation 5.
Summary and Conclusions
3
Outline
? 1. Routing for Irregular Interconnection
Networks 2. Previous Work 3. A
Tree-Based Routing Architecture for Irregular
Networks 4. Performance Evaluation 5.
Summary and Conclusions
4
Irregular Interconnection Networks

• Suitable for workstation clusters
• Incrementally scalable
• Composed of many small switches

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Architecture of Irregular Networks

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Communication Switches

• Each link connected to a computing element or a
  communication switch
• Routing decision determines the destined output
  port for each arriving packet

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Our Goal

• Design a routing scheme for irregular
• interconnection networks
• High-throughput low-latency communication
• Efficient implementation
• Works for any topologies
• Deadlock-free

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Outline
1. Routing for Irregular Interconnection
Networks ? 2. Previous Work 3. A
Tree-Based Routing Architecture for Irregular
Networks 4. Performance Evaluation 5.
Summary and Conclusions
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DEC Autonet

• Up/down routing
• A spanning tree constructed and each node with an
  ID
• Each link assigned a direction according to node
  IDs
• Each packet routed for zero or more hops in the
  up direction, and then for zero or more hops in
  the down direction
• Problems
• Waste bandwidth of unused links
• Require a routing table in the switch

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Adaptive Trail

• Adaptive trail routing
• Two unidirectional adaptive trails constructed
  from two opposite unidirectional Eulerian trails
• Links not in the trails may be used as shortcuts
• Problems
• Require a routing table in the switch
• Complex to construct the routing table

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Outline
1. Routing for Irregular Interconnection
Networks 2. Previous Work ? 3. A
Tree-based Routing Architecture for Irregular
Networks 4. Performance Evaluation 5.
Summary and Conclusions
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A New Routing Scheme for Irregular Networks

• Tree-based Routing Architecture for Irregular
• Networks (TRAIN)
• A tree is constructed from a subset of the
  network
• Links not belonging to the tree become shortcuts
  to route packets
• Deadlock-free
• No routing table is required in the switch
• Efficient implementation

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TRAIN Routing Scheme

• A tree is constructed (not necessarily binary
  tree)
• Node ID assignment
• All the links not in the tree become shortcuts
  (dotted links)
• When a packet arrives, routing
• hardware decides if a shortcut
• can provide shorter route

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TRAIN Routing Scheme (contd)

• Example a packet traverses from node 121 to node
  220
• When arriving in node 120, the switch finds that
  the
• shortcut leading to node 200 reduce the distance
• Original route takes 5 hops, while
• new route takes 3 hops
• Note that a packet may
• utilize more than one
• shortcut along the route

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TRAIN Routing Scheme (contd)
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Requirements

• Neighboring nodes IDs are stored in the switch
• Efficient distance calculation between two nodes
  (done by the routing decision hardware)

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Distance Calculation between Two Nodes
Step 1 Remove common prefix strings from the
the two nodes IDs Step 2 Distance
total number of non-zero
digits Example compare 100 ? 220 and 200 ? 220
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Network Configuration
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Deadlock Freedom

• Virtual cut-through switching is assumed (such
  that a blocked packet can never cross more than
  one node)
• No channel dependency cycle is formed (proof
  omitted)

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Outline
1. Routing for Irregular Interconnection
Networks 2. Previous Work 3. A
Tree-based Routing Architecture for Irregular
Networks ? 4. Performance Evaluation 5.
Summary and Conclusions
21
Performance Evaluation

• Latency analysis for unloaded (empty) networks
• Simulation for loaded networks
• Schemes evaluated include
• 1. Shortest path (optimal but not deadlock-free)
• 2. TRAIN
• 3. Autonet
• 4. Adaptive Trail

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Latency Analysis

• Measures
• - average base network latency
• - minimum base network latency (best tree
• configuration for each network)
• Case 1
• - 50 randomly generated networks
• - Each network composed of 16 nodes and 32 links
• - Four port switches
• Case 2
• - 50 randomly generated networks
• - Each network composed of 16 nodes and 26
  links
• - Four port switches

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Latency Analysis Case 1

• 50 randomly generated networks
• Each network composed of 16 nodes and 32 links
• Four port switches
• Shortest Path TRAIN Autonet Tree
• Avg. 1.97 2.31 2.87 3.19
• Lat.
• Avg.
• Min. 1.97 2.26 2.71
  3.04
• Lat.

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Latency Analysis Case 2

• 50 randomly generated networks
• Each network composed of 16 nodes and 26 links
• Four port switches
• Shortest Path TRAIN Autonet Tree
• Avg. 2.31 2.61 3.11 3.41
• Lat.
• Avg.
• Min. 2.31 2.53 2.90
  3.12
• Lat.

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Simulations

• Measures
• - average latency
• - normalized throughput
• Each simulation run terminated after 5000 packets
  arrive at destination
• First 2000 packets are not counted to remove
  start-up effects
• Three cases varying the numbers of nodes and
  links in the network

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Simulation Case 1

• 16 nodes
• 32 links

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Simulation Case 2

• 16 nodes
• 26 links

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Simulation Case 3

• 32 nodes
• 64 links

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Summary and Conclusions

• A cost-effective deadlock-free routing scheme is
  proposed - TRAIN
• Use algorithmic routing function to decide the
  next hop adaptively
• No routing table required and hence fast routing
  decision
• Analysis and simulation show superior performance
  to previously proposed schemes