diff --git a/defaults/main.yml b/defaults/main.yml
index 96d387f9..5034a918 100644
--- a/defaults/main.yml
+++ b/defaults/main.yml
@@ -60,10 +60,14 @@ nova_rpc_thread_pool_size: 64
 nova_rpc_conn_pool_size: 30
 nova_rpc_response_timeout: 60
 
-## Nova virtualization Type Autodetect, set to True if nova_virt_type is not set
+## Nova virtualization Type Autodetect
+# Set to True if nova_virt_type is not defined, then it will auto
+# choose kvm or qemu for nova_virt_type according to /proc/cpuinfo
 nova_virt_autodetect: True
 
 ## Nova virtualization Type, set to KVM if supported
+# Current supported choice: qemu or kvm
+# Once nova_virt_type is defined, then nova_virt_autodetect won't work any more
 nova_virt_type: kvm
 
 ## Nova Auth