Round durations in GenericBackendV2

[ElePT]

Summary

This PR makes sure that the conversion of GenericBackendV2 instruction durations to dt is exact to avoid user warnings during scheduling of type:

UserWarning: Duration is rounded to 616 [dt] = 1.367520e-07 [s] from 1.366887e-07 [s]

Given that the durations are sampled randomly, and the rounded duration is the one used in the scheduling passes, we might as well make sure in advance that the conversion from seconds to dt will be exact and doesn't raise warnings.

Details and comments

I am not sure this qualifies as a bugfix but I think it improves the readability of the test logs. For example, for test_scheduling_backend_v2 in test/python/compiler/test_transpiler.py. Before:

/Users/ept/qiskit_workspace/qiskit/qiskit/circuit/duration.py:37: UserWarning: Duration is rounded to 986 [dt] = 2.188920e-07 [s] from 2.189841e-07 [s]
  warnings.warn(
/Users/ept/qiskit_workspace/qiskit/qiskit/circuit/duration.py:37: UserWarning: Duration is rounded to 2740 [dt] = 6.082800e-07 [s] from 6.083383e-07 [s]
  warnings.warn(
/Users/ept/qiskit_workspace/qiskit/qiskit/circuit/duration.py:37: UserWarning: Duration is rounded to 2697 [dt] = 5.987340e-07 [s] from 5.988312e-07 [s]
  warnings.warn(
/Users/ept/qiskit_workspace/qiskit/qiskit/circuit/duration.py:37: UserWarning: Duration is rounded to 178 [dt] = 3.951600e-08 [s] from 3.956636e-08 [s]
  warnings.warn(
.
----------------------------------------------------------------------
Ran 1 test in 0.548s

OK

After:

.
----------------------------------------------------------------------
Ran 1 test in 0.506s

OK

[qiskit-bot]

One or more of the the following people are requested to review this:

• @Qiskit/terra-core

[coveralls]

Pull Request Test Coverage Report for Build 8392874457

Details

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.02%) to 89.321%

---

Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/lex.rs	3	91.86%

Totals
Change from base Build 8391327735:	0.02%
Covered Lines:	59794
Relevant Lines:	66943

---

💛 - Coveralls

[jakelishman]

This feels sufficiently non-critical to me that my vote would be to merge it in 1.0.1 rather than post-rc, but I don't feel overly strongly.

[jakelishman]

Technically this can cause the duration to fall outside the distribution it was drawn from. I don't know how much you care about that particular edge case, but strictly it's possible. Consider drawing from the uniform distribution [0.09, 0.15) with dt=0.04 - value arbitrarily close to 0.09 and 0.15 will be rounded to 0.08 and 0.16 respectively, outside the range.

[kevinhartman]

@ElePT perhaps you can clamp the result to the lower and upper bounds here, and ensure those bounds are a multiple of dt when declaring the constants for the ranges?

[ElePT]

Thanks for your suggestion @kevinhartman, I applied it in 0bb2fcd.

[kevinhartman]

This looks good to me. Thanks for the changes! 😄