Directly use psutil to get total system memory (#2002)

Currently Aer is using Qiskit's local_hardware_info() function which to
determine the total amount of system memory which is used to compute the
largest statevector the system can build. However, this function wasn't
really intended to be used outside of Qiskit and also Qiskit is looking
to remove the memory reporting (see: Qiskit/qiskit#11254). This commit
just pivots to using psutil directly which is what qiskit is doing
internally.

qiskit_aer/backends/backend_utils.py

@@ -16,16 +16,18 @@
 """
 import os
 from math import log2
-from qiskit.utils import local_hardware_info
+
+import psutil
 from qiskit.circuit import QuantumCircuit
 from qiskit.compiler import assemble
 from qiskit.qobj import QasmQobjInstruction
 from qiskit.result import ProbDistribution
 from qiskit.quantum_info import Clifford
+
 from .compatibility import Statevector, DensityMatrix, StabilizerState, Operator, SuperOp
 
 # Available system memory
-SYSTEM_MEMORY_GB = local_hardware_info()["memory"]
+SYSTEM_MEMORY_GB = psutil.virtual_memory().total / (1024**3)
 
 # Max number of qubits for complex double statevector
 # given available system memory

qiskit_aer/backends/statevector_simulator.py

@@ -16,7 +16,8 @@
 import copy
 import logging
 from warnings import warn
-from qiskit.utils import local_hardware_info
+
+import psutil
 from qiskit.providers.options import Options
 from qiskit.providers.models import QasmBackendConfiguration
 
@@ -364,7 +365,7 @@ def _validate(self, qobj):
         if n_qubits > max_qubits:
             raise AerError(
                 f"Number of qubits ({n_qubits}) is greater than max ({max_qubits}) "
-                f'for "{name}" with {int(local_hardware_info()["memory"])} GB system memory.'
+                f'for "{name}" with {int(psutil.virtual_memory().total / (1024**3))} GB system memory.'
             )
 
         if qobj.config.shots != 1:

qiskit_aer/backends/unitary_simulator.py

@@ -17,7 +17,8 @@
 import copy
 import logging
 from warnings import warn
-from qiskit.utils import local_hardware_info
+
+import psutil
 from qiskit.providers.options import Options
 from qiskit.providers.models import QasmBackendConfiguration
 
@@ -351,7 +352,7 @@ def _validate(self, qobj):
             raise AerError(
                 f"Number of qubits ({n_qubits}) is greater than "
                 f'max ({max_qubits}) for "{name}" with '
-                f"{int(local_hardware_info()['memory'])} GB system memory."
+                f"{int(psutil.virtual_memory().total / (1024**3))} GB system memory."
             )
         if qobj.config.shots != 1:
             logger.info('"%s" only supports 1 shot. Setting shots=1.', name)

releasenotes/notes/psutil-added-ffb2a4b5956fa03d.yaml

@@ -0,0 +1,9 @@
+---
+upgrade:
+  - |
+    Added `psutil <https://pypi.org/project/psutil/>`__ as a dependency for
+    Qiskit Aer. This is used to determine the amount of physical resources
+    available. ``psutil`` is currently a dependency of Qiskit, which is a
+    requirement for Qiskit Aer, so ``psutil`` was effectively already required
+    for any ``qiskit-aer`` installation. But, as qiskit-aer is now using it
+    directly is now a direct dependency for ``qiskit-aer``.

setup.py

@@ -25,6 +25,7 @@
     "qiskit>=0.44.0",
     "numpy>=1.16.3",
     "scipy>=1.0",
+    "psutil>=5",
 ]
 
 classifiers = [