libvirt: Add NUMA cell count to cpu_info

Adds the number of NUMA cells from libvirt to the cpu_info['topology']
attribute, so that clients using that data for socket/core/thread
counting on hypervisors can get better-quality results.

Closes-Bug: 1156456
Change-Id: I945f32bce96f27939d39b86af6ccec73b754f886

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

@@ -9568,6 +9568,7 @@ class LibvirtConnTestCase(test.NoDBTestCase):
             cpu.vendor = "AMD"
             cpu.arch = arch.X86_64
 
+            cpu.cells = 1
             cpu.cores = 2
             cpu.threads = 1
             cpu.sockets = 4
@@ -9600,7 +9601,8 @@ class LibvirtConnTestCase(test.NoDBTestCase):
                 "features": set(["extapic", "3dnow"]),
                 "model": "Opteron_G4",
                 "arch": arch.X86_64,
-                "topology": {"cores": 2, "threads": 1, "sockets": 4}}
+                "topology": {"cells": 1, "cores": 2, "threads": 1,
+                             "sockets": 4}}
         got = drvr._get_cpu_info()
         self.assertEqual(want, got)
 

nova/virt/libvirt/driver.py

@@ -4717,6 +4717,7 @@ class LibvirtDriver(driver.ComputeDriver):
         cpu_info['vendor'] = caps.host.cpu.vendor
 
         topology = dict()
+        topology['cells'] = len(getattr(caps.host.topology, 'cells', [1]))
         topology['sockets'] = caps.host.cpu.sockets
         topology['cores'] = caps.host.cpu.cores
         topology['threads'] = caps.host.cpu.threads