Remove list searches in CouplingMap.distance() #5294
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Previously, the CouplingMap.distance() method was checking whether the qubit number was in the coupling graph by searching over a list for the coupling map indices. This search becomes a bottleneck at large qubit numbers because in the worst case it has to traverse the entire list to find a match. This also is unecessary because the coupling map indices are always an ordered range from 0 to n for n qubits. This commit fixes this bottleneck by updating the check to just error if the index is out of bounds for the size of the graph. Related to Qiskit#5197
mtreinish
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Nov 16, 2020
In sabre_swap the comprehension in _score_heuristic() with the basic heuristic starts to become a bottleneck as the size of the coupling map increases. This probably becomes the top bottleneck in a transpilation after Qiskit#5316, Qiskit#5183, Qiskit#5294, Qiskit#5267, and Qiskit#5272 are merged. This commit is an attempt to try and mitigate that a bit by using numpy native operations instead of a python comprehension in sum(). If this is insufficient we'll likely have to either avoid doing a sum like this or drop down to a lower level with cython or rust and operate on the array directly to remove this bottleneck.
kdk
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Nov 24, 2020
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| if physical_qubit1 >= self.size(): | ||
| raise CouplingError("%s not in coupling graph" % physical_qubit1) | ||
| if physical_qubit2 >= self.size(): | ||
| raise CouplingError("%s not in coupling graph" % physical_qubit2) |
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Would it make sense to likewise check if0 > physical_qubit1 here?
ajavadia
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Nov 25, 2020
mergify bot
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Nov 25, 2020
* Use numpy sum instead of comprehension in _score_heuristic In sabre_swap the comprehension in _score_heuristic() with the basic heuristic starts to become a bottleneck as the size of the coupling map increases. This probably becomes the top bottleneck in a transpilation after #5316, #5183, #5294, #5267, and #5272 are merged. This commit is an attempt to try and mitigate that a bit by using numpy native operations instead of a python comprehension in sum(). If this is insufficient we'll likely have to either avoid doing a sum like this or drop down to a lower level with cython or rust and operate on the array directly to remove this bottleneck. * Make distance matrix a coupling map property * Fix tests * Fix lint Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
1ucian0
approved these changes
Dec 4, 2020
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Summary
Previously, the
CouplingMap.distance()method was checking whether thequbit number was in the coupling graph by searching over a list for the
coupling map indices. This search becomes a bottleneck at large qubit
numbers because in the worst case it has to traverse the entire list to
find a match. This also is unnecessary because the coupling map indices
are always an ordered range from 0 to n for n qubits. This commit fixes
this bottleneck by updating the check to just error if the index is out
of bounds for the size of the graph.
Details and comments
Related to #5197