X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;f=FAQ;h=2912ae335d1abdb9e5ae5e39ff586a7058da7200;hb=ac60863f78e412004c5b69f5a64a49bc6f0bc46d;hp=8b1ccb41578fecd1518d7e6ab2ec4f0d27afd600;hpb=e5f1da19948e761e44bb1bce283dd134c56e7b43;p=sliver-openvswitch.git
diff --git a/FAQ b/FAQ
index 8b1ccb415..2912ae335 100644
--- 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?
@@ -419,7 +418,11 @@ A: First, why do you want to do this? Two connected bridges are not
ports will not work with the userspace datapath, only with the
kernel module.
-Q: Why are there so many different ways to dump flows?
+
+Implementation Details
+----------------------
+
+Q: I hear OVS has a couple of kinds of flows. Can you tell me about them?
A: Open vSwitch uses different kinds of flows for different purposes:
@@ -435,18 +438,27 @@ A: Open vSwitch uses different kinds of flows for different purposes:
about hidden flows.)
- The Open vSwitch software switch implementation uses a second
- kind of flow internally. These flows, called "exact-match"
- or "datapath" or "kernel" flows, do not support wildcards or
- priorities and comprise only a single table, which makes them
- suitable for caching. OpenFlow flows and exact-match flows
+ kind of flow internally. These flows, called "datapath" or
+ "kernel" flows, do not support priorities and comprise only a
+ single table, which makes them suitable for caching. (Like
+ OpenFlow flows, datapath flows do support wildcarding, in Open
+ vSwitch 1.11 and later.) OpenFlow flows and datapath flows
also support different actions and number ports differently.
- Exact-match flows are an implementation detail that is
- subject to change in future versions of Open vSwitch. Even
- with the current version of Open vSwitch, hardware switch
- implementations do not necessarily use exact-match flows.
+ Datapath flows are an implementation detail that is subject to
+ change in future versions of Open vSwitch. Even with the
+ current version of Open vSwitch, hardware switch
+ implementations do not necessarily use this architecture.
+
+ Users and controllers directly control only the OpenFlow flow
+ table. Open vSwitch manages the datapath flow table itself, so
+ users should not normally be concerned with it.
+
+Q: Why are there so many different ways to dump flows?
- Each of the commands for dumping flows has a different purpose:
+A: Open vSwitch has two kinds of flows (see the previous question), so
+ it has commands with different purposes for dumping each kind of
+ flow:
- "ovs-ofctl dump-flows
" dumps OpenFlow flows, excluding
hidden flows. This is the most commonly useful form of flow
@@ -457,7 +469,7 @@ A: Open vSwitch uses different kinds of flows for different purposes:
including hidden flows. This is occasionally useful for
troubleshooting suspected issues with in-band control.
- - "ovs-dpctl dump-flows [dp]" dumps the exact-match flow table
+ - "ovs-dpctl dump-flows [dp]" dumps the datapath flow table
entries for a Linux kernel-based datapath. In Open vSwitch
1.10 and later, ovs-vswitchd merges multiple switches into a
single datapath, so it will show all the flows on all your
@@ -465,8 +477,29 @@ A: Open vSwitch uses different kinds of flows for different purposes:
useful for debugging.
- "ovs-appctl dpif/dump-flows
", new in Open vSwitch 1.10,
- dumps exact-match flows for only the specified bridge,
- regardless of the type.
+ dumps datapath flows for only the specified bridge, 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