Addition of Custom Topology and Custom Routing Algorithms to Constellation #85
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| * using BFS and restricts flow transitions to only those that follow the precomputed | ||
| * shortest-path next hop. No deadlock avoidance mechanism is enforced. | ||
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| * If multiple virtual channels (VCs) are available, this router assigns flows to |
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I actually think the VC allocation policy should not be determined here, it should be done by which implementation of the VCallocator class is chosen. The default might be a PriorityEncoder, but some of the variants use LSFRs (with some logic cost).
I think this approach actually would be more HW-efficient than a LSFR, perhaps, since the randomly assigned flow is chosen statically, rather than dynamically. But this might not be able to load-balance as well as the dynamic approach.
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Would you suggest making a new VC allocator?
The current hashing scheme was meant to assist the PrioritizingVCAllocator to achieve better VC utilization. However, I realized afterwards that we are actually using the RotatingVCAllocator (the default allocator) in our tapeout so this utilization scheme has actually not been tested yet.
I can also remove the getPrio() function similar to some of the other routing relations.
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The original intention of PrioritizingVCAllocator was to avoid sticking flows into escape VCs while non-escape VCs are available, I didn't think it would be used to load-balance across VCs (although it does make sense).
I think we can leave it in, although my intuition is that a better approach is to do a "PriotizingISLIP" or "PrioritizingPIM" allocator that avoids allocating the escape VC, then dynamically load-balances across the non-escape VCs.
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Would you be willing to add some text on this to the documentation? in I think CustomTopology should be another sub-section under Topology, and the auto-deadlock-free routing generator should be mentioned under the routing section. |
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I added some documentation in |
This pull request introduces a CustomTopology in
Topologies.scala. This class allows anyone to create any NoC topology by specifying the number of nodes and all the edges present in the network graph.There are 3 new routing relations,
CustomLayeredRouting,ShortestPathGeneralizedDatelineRouting, andShortestPathRouting. The first two algorithms are deadlock free on any arbitrary graph/topology while theShortestPathRoutingis not deadlock free. However it can be used in combination withEscapeChannelRouting.The new routing relations call helper methods from classes defined in
RoutingHelpers.scala. There are some tests provided in theCustomConfigs.scalahowever an exhaustive suite is not present at the moment.