libvirt: let CPUs be power managed

Before going further, we need to somehow return the list of CPUs even offline
if they are power managed by Nova.

Co-Authored-By: Sean Mooney <smooney@redhat.com>
Partially-Implements: blueprint libvirt-cpu-state-mgmt
Change-Id: I5dca10acde0eff554ed139587aefaf2f5fad2ca5

nova/conf/libvirt.py

@@ -1479,6 +1479,9 @@ Related options:
 ]
 
 libvirt_cpu_mgmt_opts = [
+    cfg.BoolOpt('cpu_power_management',
+                default=False,
+                help='Use libvirt to manage CPU cores performance.'),
     cfg.StrOpt('cpu_power_governor_low',
                default='powersave',
                help='Governor to use in order '

nova/tests/unit/virt/libvirt/test_driver.py

@@ -9190,6 +9190,34 @@ class LibvirtConnTestCase(test.NoDBTestCase,
         drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
         self.assertRaises(exception.Invalid, drvr._get_pcpu_available)
 
+    @mock.patch('nova.virt.libvirt.host.Host.get_available_cpus',
+                return_value=set([0, 1, 2, 3]))
+    def test_get_pcpu_available_for_power_mgmt(self, get_available_cpus):
+        """Test what happens when the '[compute] cpu_dedicated_set' config
+        option is set and power management is defined.
+        """
+        self.flags(vcpu_pin_set=None)
+        self.flags(cpu_dedicated_set='2-3', cpu_shared_set=None,
+                   group='compute')
+        self.flags(cpu_power_management=True, group='libvirt')
+        drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
+        pcpus = drvr._get_pcpu_available()
+        self.assertEqual(set([2, 3]), pcpus)
+
+    @mock.patch('nova.virt.libvirt.host.Host.get_available_cpus',
+                return_value=set([4, 5]))
+    def test_get_pcpu_available__cpu_dedicated_set_invalid_for_pm(self,
+            get_available_cpus):
+        """Test what happens when the '[compute] cpu_dedicated_set' config
+        option is set but it's invalid with power management set.
+        """
+        self.flags(vcpu_pin_set=None)
+        self.flags(cpu_dedicated_set='4-6', cpu_shared_set=None,
+                   group='compute')
+        self.flags(cpu_power_management=True, group='libvirt')
+        drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
+        self.assertRaises(exception.Invalid, drvr._get_pcpu_available)
+
     @mock.patch('nova.virt.libvirt.host.Host.get_online_cpus',
                 return_value=set([0, 1, 2, 3]))
     def test_get_vcpu_available(self, get_online_cpus):

nova/tests/unit/virt/libvirt/test_host.py

@@ -1052,6 +1052,12 @@ Active:          8381604 kB
              'iowait': 6121490000000},
             stats)
 
+    @mock.patch.object(fakelibvirt.virConnect, "getCPUMap")
+    def test_get_available_cpus(self, mock_map):
+        mock_map.return_value = (4, [True, True, False, False], None)
+        result = self.host.get_available_cpus()
+        self.assertEqual(result, {0, 1, 2, 3})
+
     @mock.patch.object(fakelibvirt.virConnect, "defineXML")
     def test_write_instance_config(self, mock_defineXML):
         fake_dom_xml = """

nova/virt/libvirt/driver.py

@@ -7745,15 +7745,18 @@ class LibvirtDriver(driver.ComputeDriver):
         if not CONF.compute.cpu_dedicated_set:
             return set()
 
-        online_cpus = self._host.get_online_cpus()
+        if CONF.libvirt.cpu_power_management:
+            available_cpus = self._host.get_available_cpus()
+        else:
+            available_cpus = self._host.get_online_cpus()
         dedicated_cpus = hardware.get_cpu_dedicated_set()
 
-        if not dedicated_cpus.issubset(online_cpus):
+        if not dedicated_cpus.issubset(available_cpus):
             msg = _("Invalid '[compute] cpu_dedicated_set' config: one or "
-                    "more of the configured CPUs is not online. Online "
-                    "cpuset(s): %(online)s, configured cpuset(s): %(req)s")
+                    "more of the configured CPUs is not available. Available "
+                    "cpuset(s): %(available)s, configured cpuset(s): %(req)s")
             raise exception.Invalid(msg % {
-                'online': sorted(online_cpus),
+                'available': sorted(available_cpus),
                 'req': sorted(dedicated_cpus)})
 
         return dedicated_cpus

nova/virt/libvirt/host.py

@@ -740,6 +740,14 @@ class Host(object):
 
         return doms
 
+    def get_available_cpus(self):
+        """Get the set of CPUs that exist on the host.
+
+        :returns: set of CPUs, raises libvirtError on error
+        """
+        cpus, cpu_map, online = self.get_connection().getCPUMap()
+        return {cpu for cpu in range(cpus)}
+
     def get_online_cpus(self):
         """Get the set of CPUs that are online on the host