Prefer non-PCI host nodes for non-PCI instances

When trying to fit an instance's topology to a host's, various
permutations of the host are attempted in the hope of finding one that
can be used. Modify this iteration to try use cells without a PCI
device attached first when we don't require PCI devices.

Change-Id: I8be6bf8c437fc801499b213c2e884defb7900b17
Implements: blueprint reserve-numa-with-pci

nova/tests/unit/virt/test_hardware.py

@@ -13,6 +13,7 @@
 # under the License.
 
 import collections
+import copy
 
 import mock
 from oslo_serialization import jsonutils
@@ -25,6 +26,7 @@ from nova.objects import base as base_obj
 from nova.objects import fields
 from nova.pci import stats
 from nova import test
+from nova.tests.unit import fake_pci_device_pools as fake_pci
 from nova.tests import uuidsentinel as uuids
 from nova.virt import hardware as hw
 
@@ -1782,6 +1784,33 @@ class VirtNUMAHostTopologyTestCase(test.NoDBTestCase):
                                                         pci_stats=pci_stats)
             self.assertIsNone(fitted_instance1)
 
+    def test_get_fitting_pci_avoided(self):
+
+        def _create_pci_stats(node):
+            test_dict = copy.copy(fake_pci.fake_pool_dict)
+            test_dict['numa_node'] = node
+            return stats.PciDeviceStats(
+                [objects.PciDevicePool.from_dict(test_dict)])
+
+        # the PCI device is found on host cell 1
+        pci_stats = _create_pci_stats(1)
+
+        # ...threfore an instance without a PCI device should get host cell 2
+        instance_topology = hw.numa_fit_instance_to_host(
+                self.host, self.instance1, pci_stats=pci_stats)
+        self.assertIsInstance(instance_topology, objects.InstanceNUMATopology)
+        # TODO(sfinucan): We should be comparing this against the HOST cell
+        self.assertEqual(2, instance_topology.cells[0].id)
+
+        # the PCI device is now found on host cell 2
+        pci_stats = _create_pci_stats(2)
+
+        # ...threfore an instance without a PCI device should get host cell 1
+        instance_topology = hw.numa_fit_instance_to_host(
+                self.host, self.instance1, pci_stats=pci_stats)
+        self.assertIsInstance(instance_topology, objects.InstanceNUMATopology)
+        self.assertEqual(1, instance_topology.cells[0].id)
+
 
 class NumberOfSerialPortsTest(test.NoDBTestCase):
     def test_flavor(self):

nova/virt/hardware.py

@@ -1479,10 +1479,19 @@ def numa_fit_instance_to_host(
     if 'emulator_threads_policy' in instance_topology:
         emulator_threads_policy = instance_topology.emulator_threads_policy
 
+    host_cells = host_topology.cells
+
+    # If PCI device(s) are not required, prefer host cells that don't have
+    # devices attached. Presence of a given numa_node in a PCI pool is
+    # indicative of a PCI device being associated with that node
+    if not pci_requests and pci_stats:
+        host_cells = sorted(host_cells, key=lambda cell: cell.id in [
+            pool['numa_node'] for pool in pci_stats.pools])
+
     # TODO(ndipanov): We may want to sort permutations differently
     # depending on whether we want packing/spreading over NUMA nodes
     for host_cell_perm in itertools.permutations(
-            host_topology.cells, len(instance_topology)):
+            host_cells, len(instance_topology)):
         cells = []
         for host_cell, instance_cell in zip(
                 host_cell_perm, instance_topology.cells):