nonblocking libvirt mode using tpool

Add an option libvirt_nonblocking (disabled by default) to use a thread
pool to execute all libvirt API calls. Previously all the calls except
one in firewall.py are blocking in the eventlet thread model.

Change-Id: I665ed7a629bb029011b181e8d2844fc2276502d9

3 files changed, 23 insertions, 2 deletions

diff --git a/etc/nova/nova.conf.sample b/etc/nova/nova.conf.sample
index 1ff6ec357..afdedfbd3 100644
--- a/etc/nova/nova.conf.sample
+++ b/etc/nova/nova.conf.sample
@@ -740,6 +740,8 @@
 # libvirt_disk_prefix=<None>
 ###### (BoolOpt) Inject the admin password at boot time, without an agent.
 # libvirt_inject_password=false
+###### (BoolOpt) Use a separated OS thread pool to realize non-blocking libvirt calls. Disabled by default.
+# libvirt_nonblocking=false
 ###### (StrOpt) Libvirt domain type (valid options are: kvm, lxc, qemu, uml, xen)
 # libvirt_type="kvm"
 ###### (StrOpt) Override the default libvirt URI (which is dependent on libvirt_type)
diff --git a/nova/virt/libvirt/connection.py b/nova/virt/libvirt/connection.py
index 5603b1e26..58154c4a4 100644
--- a/nova/virt/libvirt/connection.py
+++ b/nova/virt/libvirt/connection.py
@@ -50,6 +50,8 @@ import time
 import uuid
 
 from eventlet import greenthread
+from eventlet import tpool
+
 from xml.dom import minidom
 from xml.etree import ElementTree
 
@@ -154,6 +156,10 @@ libvirt_opts = [
                help='Number of seconds to wait for instance to shut down after'
                     ' soft reboot request is made. We fall back to hard reboot'
                     ' if instance does not shutdown within this window.'),
+    cfg.BoolOpt('libvirt_nonblocking',
+                default=False,
+                help='Use a separated OS thread pool to realize non-blocking'
+                     ' libvirt calls')
     ]
 
 FLAGS = flags.FLAGS
@@ -249,9 +255,16 @@ class LibvirtConnection(driver.ComputeDriver):
     def _get_connection(self):
         if not self._wrapped_conn or not self._test_connection():
             LOG.debug(_('Connecting to libvirt: %s'), self.uri)
-            self._wrapped_conn = self._connect(self.uri,
+            if not FLAGS.libvirt_nonblocking:
+                self._wrapped_conn = self._connect(self.uri,
                                                self.read_only)
+            else:
+                self._wrapped_conn = tpool.proxy_call(
+                    (libvirt.virDomain, libvirt.virConnect),
+                    self._connect, self.uri, self.read_only)
+
         return self._wrapped_conn
+
     _conn = property(_get_connection)
 
     def _test_connection(self):
diff --git a/nova/virt/libvirt/firewall.py b/nova/virt/libvirt/firewall.py
index 04b3cf42a..dd491ea5f 100644
--- a/nova/virt/libvirt/firewall.py
+++ b/nova/virt/libvirt/firewall.py
@@ -144,7 +144,13 @@ class NWFilterFirewall(base_firewall.FirewallDriver):
         if callable(xml):
             xml = xml()
         # execute in a native thread and block current greenthread until done
-        tpool.execute(self._conn.nwfilterDefineXML, xml)
+        if not FLAGS.libvirt_nonblocking:
+            # NOTE(maoy): the original implementation is to have the API called
+            # in the thread pool no matter what.
+            tpool.execute(self._conn.nwfilterDefineXML, xml)
+        else:
+            # NOTE(maoy): self._conn is a eventlet.tpool.Proxy object
+            self._conn.nwfilterDefineXML(xml)
 
     def unfilter_instance(self, instance, network_info):
         """Clear out the nwfilter rules."""