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README.md

OpenVINO Hetero Plugin Design Overview

Subgraphs selection

Algorithm:

For each plugin

  1. Select root node
    • A node not in a previously constructed subgraph
    • Affinity is equal to the plugin name
  2. Select an adjacent node to any node in a present subgraph which is not on the rejected list
    • If there are no such nodes end
  3. Verify that the selected node has the same affinity
  4. Add a node to a subgraph if the check has been successful or add to the rejected list otherwise
  5. Check a global condition
    • Nodes in the rejected list can never be added to a subgraph
    • Nodes not in a subgraph and not in the rejected list can possibly be added later
    • Check the subgraph topology (the only check now is whether there are no indirect subgraph self-references)
  6. If a global condition has failed, remove the last node from a subgraph. Add it to the rejected list and go to step 5.
    • we can rollback multiple times here because rejected list is changed every time
  7. Go to step 2

Example:

graph TD;
    1-->2;
    2-->3;
    2-->4;
    3-->5;
    4-->5;
    5-->6;
    6-->7;
Loading

Nodes [1,2,3,5,6,7] are supported in the plugin, [4] is not

Possible roots: [1,2,3,5,6,7]

  1. Select root [1]
    • Subgraph: [1]
    • Rejected: []
    • Global condition: ok
  2. Merge [2]
    • Subgraph: [1,2]
    • Rejected: []
    • Global condition: ok
  3. Merge [3]
    • Subgraph: [1,2,3]
    • Rejected: []
    • Global condition: ok
  4. Merge [5]
    • Subgraph: [1,2,3,5]
    • Rejected: []
    • Global condition: There are possible self-references throughout a node [4] but they are not known yet, ok
  5. Merge [6]
    • Subgraph: [1,2,3,5,6]
    • Rejected: []
    • Global condition: There are possible self-references throughout a node [4] but they are not known yet, ok
  6. Merge [7]
    • Subgraph: [1,2,3,5,6,7]
    • Rejected: []
    • Global condition: There are possible self-references throughout a node [4] but they are not known yet, ok
  7. Failed to merge [4]
    • Subgraph: [1,2,3,5,6,7]
    • Rejected: [4]
    • Global condition: There are self-references throughout a node [4], reject
  8. Rollback [7]
    • Subgraph: [1,2,3,5,6]
    • Rejected: [4,7]
    • Global condition: There are self-references throughout a node [4], reject
  9. Rollback [6]
    • Subgraph: [1,2,3,5]
    • Rejected: [4,6,7]
    • Global condition: There are self-references throughout a node [4], reject
  10. Rollback [5]
    • Subgraph: [1,2,3]
    • Rejected: [4,5,6,7]
    • Global condition: ok
  11. There are nodes to merge end

Possible roots: [5,6,7]

  1. Select root [5]
    • Subgraph: [5]
    • Rejected: []
    • Global condition: ok
  2. Merge [6]
    • Subgraph: [5,6]
    • Rejected: []
    • Global condition: ok
  3. Merge [7]
    • Subgraph: [5,6,7]
    • Rejected: []
    • Global condition: ok
  4. Merge [3]
    • Subgraph: [3,5,6,7]
    • Rejected: []
    • Global condition: ok
  5. Merge [2]
    • Subgraph: [2,3,5,6,7]
    • Rejected: []
    • Global condition: There are possible self-references throughout a node [4] but they are not known yet, ok
  6. Failed to merge [4]
    • Subgraph: [2,3,5,6,7]
    • Rejected: [4]
    • Global condition: There are self-references throughout a node [4], reject
  7. Rollback [2]
    • Subgraph: [3,5,6,7]
    • Rejected: [2,4]
    • Global condition: ok
  8. There are nodes to merge end

Possible roots: [] no roots, END

Subgraphs: [1,2,3], [3,5,6,7]

Select best subgraph:

  • When there are multiple subgraphs, a larger one ([3,5,6,7]) is always selected.

Repeat previous steps with remaining nodes [1,2]

The final result is:

  • First plugin: [3,5,6,7], [1,2]
  • Second plugin: [4]

Subgraphs self reference detection

  1. For each node in a network build a list of reachable nodes (transitive closure).
  2. For each pair of nodes in a subgraph find path nodes (nodes through one node in pair reachable to other).
    • assume src - one node in a pair, dst - other node in a pair
    • get all reachable nodes from src
    • in the nodes find nodes through which you can reach dst. These will be the path nodes.
  3. Results for pairs are cached.
  4. Check whether there is an intersection between path nodes set and rejected nodes set for each pair of nodes in a subgraph.
  5. If an intersection happens, a self-reference occurs, and a subgraph is invalid.

See also