Add more default trials to sabre layout #13360
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Right now sabre layout uses n random trials (as specified by the user or defaulting to num_cpus) and since Qiskit#12453 one additional trial taking the qubits of the densest subgraph as a starting point. There are also a couple of other trivial examples to try which may or may not produce better results depending on the circuit, a trivial layout and a reverse trivial layout. In the case of a hardware efficient circuit the trivial layout will map exactly and would always be picked. When running in a preset pass manager sabre should never be called in this scenario because VF2Layout will find the mapping, but the incremental cost of adding the trial is minimal. Similarly the cost of a reversed trivial layout (where virtual qubit 0 -> n, 1 -> n - 1, etc.) is trivial and may in some scenarios produce a better results.
mtreinish
added
Changelog: New Feature
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One or more of the following people are relevant to this code:
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Pull Request Test Coverage Report for Build 11617356503Warning: This coverage report may be inaccurate.This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.
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💛 - Coveralls |
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I ran the asv from qiskit.circuit.library import EfficientSU2
from qiskit.providers.fake_provider import GenericBackendV2
from qiskit import generate_preset_pass_manager
cmap = [[0, 14], [1, 0], [1, 2], [3, 2], [4, 3], [4, 5], [6, 5], [7, 6], [8, 7], [8, 9], [8, 16], [9, 10], [11, 10], [11, 12], [12, 13], [15, 4], [16, 26], [17, 12], [17, 30], [18, 14], [18, 19], [19, 20], [21, 20], [22, 15], [22, 21], [22, 23], [23, 24], [25, 24], [25, 26], [27, 26], [27, 28], [28, 29], [28, 35], [30, 29], [30, 31], [31, 32], [32, 36], [33, 20], [33, 39], [34, 24], [34, 43], [37, 38], [38, 39], [39, 40], [40, 41], [42, 41], [43, 42], [44, 43], [44, 45], [46, 45], [47, 35], [47, 46], [48, 47], [49, 48], [49, 55], [50, 49], [50, 51], [51, 36], [52, 37], [53, 41], [53, 60], [54, 45], [54, 64], [55, 68], [56, 52], [57, 56], [57, 58], [59, 58], [59, 60], [61, 60], [62, 61], [62, 63], [63, 64], [64, 65], [65, 66], [67, 66], [67, 68], [68, 69], [70, 69], [71, 58], [72, 62], [73, 66], [73, 85], [74, 70], [75, 90], [76, 75], [76, 77], [77, 71], [77, 78], [79, 78], [79, 91], [80, 79], [81, 72], [81, 80], [82, 81], [82, 83], [83, 92], [84, 83], [84, 85], [86, 85], [87, 86], [87, 93], [88, 87], [89, 74], [89, 88], [93, 106], [94, 90], [94, 95], [96, 95], [96, 97], [96, 109], [97, 98], [98, 91], [98, 99], [99, 100], [101, 100], [101, 102], [102, 92], [102, 103], [104, 103], [104, 111], [105, 104], [105, 106], [106, 107], [107, 108], [109, 114], [110, 100], [112, 108], [113, 114], [115, 114], [116, 115], [117, 116], [118, 110], [118, 117], [119, 118], [120, 119], [121, 120], [122, 111], [122, 121], [122, 123], [124, 123], [125, 124], [125, 126], [126, 112]]
backend = GenericBackendV2(127, basis_gates=["ecr", "id", "rz", "sx", "x"], coupling_map=cmap)
qc = EfficientSU2(127, entanglement='circular', reps=3, insert_barriers=True, flatten=True)
import time
pm = generate_preset_pass_manager(2, backend=backend)
times = []
ecr_counts = []
depths = []
for i in range(25):
start = time.perf_counter()
res = pm.run(qc)
stop = time.perf_counter()
times.append(stop - start)
ecr_count = res.count_ops()["ecr"]
ecr_counts.append(ecr_count)
depth = res.depth()
depths.append(depth)
import statistics
print(f"Avg runtime: {statistics.geometric_mean(times)}")
print(f"Minimum ECR count: {min(ecr_counts)}")
print(f"Median ecr count: {statistics.median(ecr_counts)}")
print(f"Minimum depth: {min(depths)}")
print(f"Median depth: {statistics.median(depths)}")and ran it with this PR and main. On main it returned: with this PR it returned: |
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@jakelishman how comfortable are you with the sneaky HW-dependent extra trials? I see:
- Pros: better outcome for a lot of practical use cases
- Cons: it's incomplete. We might generate an expectation on users that wouldn't be met for architectures outside of the ones contemplated in the "hack".
I'm still leaning towards the yes (not only because of the xkcd reference), but I might be missing something.
Co-authored-by: Elena Peña Tapia <[email protected]>
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Note that for the 127-qubit layout we found a maximum-sized ring (over 104 qubits), and then inserted the remaining 23 qubits near their respective neighbors in the ring, while for the 133- and 156-qubit layouts we just chose a maximum-sized ring. To decide which of the two strategies is better, I have modified the script above to transpile |
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Hi @alexanderivrii, interesting! thanks for running the data. Looking (crudely) at the median depth ratios over the default strategy I see that all 3 strategies lead to some improvement in the geometric mean of the ratios:
- (2) default + linear + reverse linear layouts (in this PR) -> 0.93
- (3) default + ring over 104 qubits (not in this PR) -> 0.67
- (4) default + ring with addition qubits inserted (in this PR) -> 0.68
And I'd say the difference between 3 an 4 doesn't look significative (especially given the number of samples). If I have learned anything from the last week is that the statistical distribution of the 2q depth ratios behaves weirdly enough not to extract conclusions from its geometric mean, but in case you are curious, I got:
- (2) default + linear + reverse linear layouts (in this PR) -> 0.91
- (3) default + ring over 104 qubits (not in this PR) -> 0.64
- (4) default + ring with addition qubits inserted (in this PR) -> 0.69
Given this, and the closeness to the rc1 deadline, I would vote for merging the current state of the PR and leave changes for follow-ups.
Summary
Right now sabre layout uses n random trials (as specified by the user or defaulting to num_cpus) and since #12453 one additional trial taking the qubits of the densest subgraph as a starting point. There are also a couple of other trivial examples to try which may or may not produce better results depending on the circuit, a trivial layout and a reverse trivial layout. In the case of a hardware efficient circuit the trivial layout will map exactly and would always be picked. When running in a preset pass manager sabre should never be called in this scenario because VF2Layout will find the mapping, but the incremental cost of adding the trial is minimal. Similarly the cost of a reversed trivial layout (where virtual qubit 0 -> n, 1 -> n - 1, etc.) is trivial and may in some scenarios produce a better results.
Details and comments
TODO: