Dragonfly Interconnect Routing via Virtual Channels
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Solution Overview
Problem
In multiprocessor computer systems, existing processor interconnect networks face challenges in achieving efficient communication between processing nodes while minimizing the number of links and cost, particularly in high-radix networks where long optical channels are expensive and conventional adaptive routing algorithms lead to latency and throughput degradation due to indirect routing decisions based on remote information.
Innovation Solution
The dragonfly topology uses high-radix routers with a virtual router configuration, employing selective virtual-channel discrimination and credit-round trip latency to sense global channel congestion, reducing the number of global channels and increasing their length, thereby minimizing network cost and latency while maintaining performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional adaptive routing algorithms are used in high-radix networks, then routing flexibility is provided, but latency and throughput degradation occur due to indirect routing decisions based on remote information
Solution Approach 1:
The patent introduces virtual channels as intermediaries between physical channels and routing decisions. Virtual channels provide an intermediate layer that maps multiple physical channels to virtual channels, enabling indirect routing while reducing the impact of remote information delays. The virtual channel controller acts as a mediator that makes routing decisions based on local virtual channel state rather than directly accessing remote physical channel state.
Solution Approach 2:
The patent segments the routing decision process into local and remote components. Local routing decisions are made based on virtual channel state at the current node, while remote routing decisions are made based on virtual channel state at destination nodes. This segmentation allows routing flexibility without requiring direct access to all remote physical channel information, thereby reducing latency.
2Device complexity
If the number of global channels is reduced to minimize network cost, then cost and complexity are reduced, but routing flexibility and load balancing capability are compromised
Solution Approach 1:
The patent makes virtual channels universal by allowing them to serve multiple functions: they provide routing flexibility, enable load balancing, and work with reduced physical channel counts. The virtual channel mechanism is designed to be multi-functional, compensating for the reduced number of physical global channels through intelligent virtual channel management and mapping.
Solution Approach 2:
The patent changes the parameter space from physical channels to virtual channels. Instead of managing routing flexibility through the number of physical channels, the system manages it through virtual channel configurations. This parameter transformation allows routing flexibility to be maintained while reducing physical channel count, as virtual channels can be dynamically configured to provide necessary routing options.
3Area of stationary object
If long optical channels are used to connect remote nodes, then network coverage is extended, but cost and signal degradation increase
Solution Approach 1:
The patent introduces virtual channels as intermediaries that enable routing decisions without requiring direct long optical channel connections for all routing paths. The virtual channel mechanism allows nodes to make routing decisions based on virtual channel state rather than requiring continuous physical channel information across long distances, reducing the impact of long optical channel costs.
4Adaptability or versatility
If indirect routing decisions are made based on remote information, then routing adaptability is provided, but throughput degradation occurs due to information propagation delays
Solution Approach 1:
The patent introduces virtual channels as intermediaries that propagate routing information more efficiently. Virtual channel state information acts as a mediator between remote nodes, reducing the propagation delay impact compared to direct physical channel information. The virtual channel controller processes this intermediate information to make routing decisions that maintain adaptability while improving throughput.
Solution Approach 2:
The patent implements preliminary action by pre-configuring virtual channel mappings and routing tables. This allows routing decisions to be made based on pre-established virtual channel paths rather than requiring real-time information propagation across all physical channels, thereby maintaining routing adaptability while reducing throughput degradation from information propagation delays.
Data Source
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AI summary
A multiprocessor computer system comprises a dragonfly processor interconnect network that comprises a plurality of processor nodes and a plurality of routers. The routers are operable to route data by selecting from among a plurality of network paths from a target node to a destination node in the dragonfly network based on one or more routing tables.