cccl: A wrapper that calls visual c++ compiler.

[sliver-openvswitch.git] / FAQ

diff --git a/FAQ b/FAQ
index b81ee6c..4a8a5be 100644 (file)
--- a/FAQ
+++ b/FAQ
@@ -89,10 +89,9 @@ A: Distributed vswitch applications (e.g., VMware vNetwork distributed
    environments: OpenFlow, which exposes flow-based forwarding state,
    and the OVSDB management protocol, which exposes switch port state.
    In addition to the switch implementation itself, Open vSwitch
-   includes tools (ovs-controller, ovs-ofctl, ovs-vsctl) that developers
-   can script and extend to provide distributed vswitch capabilities
-   that are closely integrated with their virtualization management
-   platform.
+   includes tools (ovs-ofctl, ovs-vsctl) that developers can script and
+   extend to provide distributed vswitch capabilities that are closely
+   integrated with their virtualization management platform.
 
 Q: Why doesn't Open vSwitch support distribution?
 
@@ -169,7 +168,7 @@ Q: Should userspace or kernel be upgraded first to minimize downtime?
    kernel version included in the same release or with the version
    from upstream Linux.  However, when upgrading between two releases
    of Open vSwitch it is best to migrate userspace first to reduce
-   the possbility of incompatibilities.
+   the possibility of incompatibilities.
 
 Q: What features are not available in the Open vSwitch kernel datapath
    that ships as part of the upstream Linux kernel?
@@ -469,6 +468,27 @@ A: Open vSwitch uses different kinds of flows for different purposes:
         regardless of the type.
 
 
+Performance
+-----------
+
+Q: I just upgraded and I see a performance drop.  Why?
+
+A: The OVS kernel datapath may have been updated to a newer version than
+   the OVS userspace components.  Sometimes new versions of OVS kernel
+   module add functionality that is backwards compatible with older
+   userspace components but may cause a drop in performance with them.
+   Especially, if a kernel module from OVS 2.1 or newer is paired with
+   OVS userspace 1.10 or older, there will be a performance drop for
+   TCP traffic.
+
+   Updating the OVS userspace components to the latest released
+   version should fix the performance degradation.
+
+   To get the best possible performance and functionality, it is
+   recommended to pair the same versions of the kernel module and OVS
+   userspace.
+
+
 Configuration Problems
 ----------------------
 
@@ -1255,9 +1275,11 @@ A: To debug network behavior problems, trace the path of a packet,
 
 Q: How do I make a flow drop packets?
 
-A: An empty set of actions causes a packet to be dropped.  You can
-   specify an empty set of actions with "actions=" on the ovs-ofctl
-   command line.  For example:
+A: To drop a packet is to receive it without forwarding it.  OpenFlow
+   explicitly specifies forwarding actions.  Thus, a flow with an
+   empty set of actions does not forward packets anywhere, causing
+   them to be dropped.  You can specify an empty set of actions with
+   "actions=" on the ovs-ofctl command line.  For example:
 
        ovs-ofctl add-flow br0 priority=65535,actions=
 
@@ -1269,6 +1291,9 @@ A: An empty set of actions causes a packet to be dropped.  You can
 
        ovs-ofctl add-flow br0 priority=65535,actions=drop
 
+   "drop" is not an action, either in OpenFlow or Open vSwitch.
+   Rather, it is only a way to say that there are no actions.
+
 Q: I added a flow to send packets out the ingress port, like this:
 
        ovs-ofctl add-flow br0 in_port=2,actions=2