Cache [pci]alias parsing

For each lifecycle operation nova re-load, parses, and validates the
[pci]alias config option. This is wasteful. So this patch adds
functools.cache decorator on the function used to do this work.

Change-Id: If2ffb25430749a22c923c0938221833e7b883873

nova/pci/request.py

@@ -37,7 +37,7 @@
     These two aliases define a device request meaning: vendor_id is "8086" and
     product_id is "0442" or "0443".
     """
-
+import functools
 import typing as ty
 
 import jsonschema
@@ -173,6 +173,7 @@ def _validate_aliases(aliases):
     _validate_required_ids(aliases)
 
 
+@functools.cache
 def get_alias_from_config() -> Alias:
     """Parse and validate PCI aliases from the nova config.
 

nova/test.py

@@ -62,6 +62,7 @@ from nova.db.main import api as db_api
 from nova import exception
 from nova import objects
 from nova.objects import base as objects_base
+from nova.pci import request
 from nova import quota
 from nova.scheduler.client import report
 from nova.scheduler import utils as scheduler_utils
@@ -190,6 +191,10 @@ class TestCase(base.BaseTestCase):
         self.useFixture(
             nova_fixtures.PropagateTestCaseIdToChildEventlets(self.id()))
 
+        # Ensure that the pci alias is reset between test cases running in
+        # the same process
+        request.get_alias_from_config.cache_clear()
+
         # How many of which service we've started. {$service-name: $count}
         self._service_fixture_count = collections.defaultdict(int)
 
@@ -426,6 +431,10 @@ class TestCase(base.BaseTestCase):
         group = kw.pop('group', None)
         for k, v in kw.items():
             CONF.set_override(k, v, group)
+            # loading and validating alias is cached so if it is reconfigured
+            # we need to reset the cache
+            if k == 'alias' and group == 'pci':
+                request.get_alias_from_config.cache_clear()
 
     def reset_flags(self, *k, **kw):
         """Reset flag variables for a test."""

nova/tests/unit/pci/test_request.py

@@ -342,6 +342,23 @@ class PciRequestTestCase(test.NoDBTestCase):
             "product_id fields set or resource_class field set.",
             str(ex))
 
+    def test_get_alias_from_config_cached(self):
+        alias = jsonutils.dumps({
+            "name": "a5",
+            "vendor_id": "4444",
+            "product_id": "4444",
+        })
+        self.flags(alias=[alias], group='pci')
+
+        origi_loads = jsonutils.loads
+
+        with mock.patch('oslo_serialization.jsonutils.loads') as mock_loads:
+            mock_loads.side_effect = origi_loads
+            request.get_alias_from_config()
+            request.get_alias_from_config()
+
+        mock_loads.assert_called_once()
+
     def _verify_result(self, expected, real):
         exp_real = zip(expected, real)
         for exp, real in exp_real: