Add hpet option for time drifting

Since havana, the timezone of windows vm is localtime.
However, there is a time drifting when the windows vm is overloaded.
Disabling hpet option of clock in xml template,
we can sync time without buffering.

From this template,

<clock offset='utc'>
<timer name='pit' tickpolicy='delay'/>
<timer name='rtc' tickpolicy='catchup'/>
</clock>

To this template,

<clock offset='localtime'>
<timer name='rtc' tickpolicy='catchup'/>
<timer name='pit' tickpolicy='delay'/>
<timer name='hpet' present='no'/>
</clock>

Implements : blueprint add-no-hpet-option-into-guest-clock
Change-Id: I6441b9d2de5897dd1863b53bd7e2578881b53c67

nova/tests/virt/libvirt/test_libvirt.py

@@ -804,17 +804,21 @@ class LibvirtConnTestCase(test.TestCase):
         self.assertEqual(type(cfg.clock),
                          vconfig.LibvirtConfigGuestClock)
         self.assertEqual(cfg.clock.offset, "utc")
-        self.assertEqual(len(cfg.clock.timers), 2)
+        self.assertEqual(len(cfg.clock.timers), 3)
         self.assertEqual(type(cfg.clock.timers[0]),
                          vconfig.LibvirtConfigGuestTimer)
         self.assertEqual(type(cfg.clock.timers[1]),
                          vconfig.LibvirtConfigGuestTimer)
+        self.assertEqual(type(cfg.clock.timers[2]),
+                         vconfig.LibvirtConfigGuestTimer)
         self.assertEqual(cfg.clock.timers[0].name, "pit")
         self.assertEqual(cfg.clock.timers[0].tickpolicy,
                          "delay")
         self.assertEqual(cfg.clock.timers[1].name, "rtc")
         self.assertEqual(cfg.clock.timers[1].tickpolicy,
                          "catchup")
+        self.assertEqual(cfg.clock.timers[2].name, "hpet")
+        self.assertEqual(cfg.clock.timers[2].present, False)
 
     def test_get_guest_config_windows(self):
         conn = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), True)

nova/virt/libvirt/driver.py

@@ -3120,8 +3120,13 @@ class LibvirtDriver(driver.ComputeDriver):
             tmrtc.name = "rtc"
             tmrtc.tickpolicy = "catchup"
 
+            tmhpet = vconfig.LibvirtConfigGuestTimer()
+            tmhpet.name = "hpet"
+            tmhpet.present = False
+
             clk.add_timer(tmpit)
             clk.add_timer(tmrtc)
+            clk.add_timer(tmhpet)
 
         for cfg in self.get_guest_storage_config(instance,
                                                  image_meta,