Qiskit / qiskit / 9426882578

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Commit Message

Fix unnecessary serialisation of `PassManager` in serial contexts (backport #12410) (#12500)

* Fix unnecessary serialisation of `PassManager` in serial contexts (#12410)

* Fix unnecessary serialisation of `PassManager` in serial contexts

This exposes the interal decision in `parallel_map` of whether to
actually run in serial or not.  If not, there's no need for
`PassManager` to side-car its `dill` serialisation onto the side of the
IPC (we use `dill` because we need to pickle lambdas), which can be an
unfortunately huge cost for certain IBM pulse-enabled backends.

* Remove new function from public API

This makes the patch series safe for backport to 1.1.

(cherry picked from commit b12e9ec3c)

# Conflicts:
#	qiskit/utils/__init__.py
#	qiskit/utils/parallel.py

* solve conflicts

* passmanager does not know the cpu_count

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Co-authored-by: Jake Lishman <jake.lishman@ibm.com>
Co-authored-by: Luciano Bello <bel@zurich.ibm.com>

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43 existing lines in 6 files now uncovered.

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