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f54d8f004f
This commit adds a number of specialized functions, that handle
common miniflow fingerprints. This enables compiler optimization,
resulting in higher performance. Below a quick description of
how this optimization actually works;
"Specialized functions" are "instances" of the generic implementation,
but the compiler is given extra context when compiling. In the case of
iterating miniflow datastructures, the most interesting value to enable
compile time optimizations is the loop trip count per unit.
In order to create a specialized function, there is a generic implementation,
which uses a for() loop without the compiler knowing the loop trip count at
compile time. The loop trip count is passed in as an argument to the function:
uint32_t miniflow_impl_generic(struct miniflow *mf, uint32_t loop_count)
{
for(uint32_t i = 0; i < loop_count; i++)
// do work
}
In order to "specialize" the function, we call the generic implementation
with hard-coded numbers - these are compile time constants!
uint32_t miniflow_impl_loop5(struct miniflow *mf, uint32_t loop_count)
{
// use hard coded constant for compile-time constant-propogation
return miniflow_impl_generic(mf, 5);
}
Given the compiler is aware of the loop trip count at compile time,
it can perform an optimization known as "constant propogation". Combined
with inlining of the miniflow_impl_generic() function, the compiler is
now enabled to *compile time* unroll the loop 5x, and produce "flat" code.
The last step to using the specialized functions is to utilize a
function-pointer to choose the specialized (or generic) implementation.
The selection of the function pointer is performed at subtable creation
time, when miniflow fingerprint of the subtable is known. This technique
is known as "multiple dispatch" in some literature, as it uses multiple
items of information (miniflow bit counts) to select the dispatch function.
By pointing the function pointer at the optimized implementation, OvS
benefits from the compile time optimizations at runtime.
Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
Tested-by: Malvika Gupta <malvika.gupta@arm.com>
Acked-by: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>
.. NOTE(stephenfin): If making changes to this file, ensure that the
start-after/end-before lines found in 'Documentation/intro/what-is-ovs'
are kept up-to-date.
============
Open vSwitch
============
.. image:: https://travis-ci.org/openvswitch/ovs.png
:target: https://travis-ci.org/openvswitch/ovs
.. image:: https://ci.appveyor.com/api/projects/status/github/openvswitch/ovs?branch=master&svg=true&retina=true
:target: https://ci.appveyor.com/project/blp/ovs/history
.. image:: https://api.cirrus-ci.com/github/openvswitch/ovs.svg
:target: https://cirrus-ci.com/github/openvswitch/ovs
What is Open vSwitch?
---------------------
Open vSwitch is a multilayer software switch licensed under the open source
Apache 2 license. Our goal is to implement a production quality switch
platform that supports standard management interfaces and opens the forwarding
functions to programmatic extension and control.
Open vSwitch is well suited to function as a virtual switch in VM environments.
In addition to exposing standard control and visibility interfaces to the
virtual networking layer, it was designed to support distribution across
multiple physical servers. Open vSwitch supports multiple Linux-based
virtualization technologies including Xen/XenServer, KVM, and VirtualBox.
The bulk of the code is written in platform-independent C and is easily ported
to other environments. The current release of Open vSwitch supports the
following features:
- Standard 802.1Q VLAN model with trunk and access ports
- NIC bonding with or without LACP on upstream switch
- NetFlow, sFlow(R), and mirroring for increased visibility
- QoS (Quality of Service) configuration, plus policing
- Geneve, GRE, VXLAN, STT, and LISP tunneling
- 802.1ag connectivity fault management
- OpenFlow 1.0 plus numerous extensions
- Transactional configuration database with C and Python bindings
- High-performance forwarding using a Linux kernel module
The included Linux kernel module supports Linux 3.10 and up.
Open vSwitch can also operate entirely in userspace without assistance from
a kernel module. This userspace implementation should be easier to port than
the kernel-based switch. OVS in userspace can access Linux or DPDK devices.
Note Open vSwitch with userspace datapath and non DPDK devices is considered
experimental and comes with a cost in performance.
What's here?
------------
The main components of this distribution are:
- ovs-vswitchd, a daemon that implements the switch, along with a companion
Linux kernel module for flow-based switching.
- ovsdb-server, a lightweight database server that ovs-vswitchd queries to
obtain its configuration.
- ovs-dpctl, a tool for configuring the switch kernel module.
- Scripts and specs for building RPMs for Citrix XenServer and Red Hat
Enterprise Linux. The XenServer RPMs allow Open vSwitch to be installed on a
Citrix XenServer host as a drop-in replacement for its switch, with
additional functionality.
- ovs-vsctl, a utility for querying and updating the configuration of
ovs-vswitchd.
- ovs-appctl, a utility that sends commands to running Open vSwitch daemons.
Open vSwitch also provides some tools:
- ovs-ofctl, a utility for querying and controlling OpenFlow switches and
controllers.
- ovs-pki, a utility for creating and managing the public-key infrastructure
for OpenFlow switches.
- ovs-testcontroller, a simple OpenFlow controller that may be useful for
testing (though not for production).
- A patch to tcpdump that enables it to parse OpenFlow messages.
What other documentation is available?
--------------------------------------
.. TODO(stephenfin): Update with a link to the hosting site of the docs, once
we know where that is
To install Open vSwitch on a regular Linux or FreeBSD host, please read the
`installation guide <Documentation/intro/install/general.rst>`__. For specifics
around installation on a specific platform, refer to one of the `other
installation guides <Documentation/intro/install/index.rst>`__
For answers to common questions, refer to the `FAQ <Documentation/faq>`__.
To learn about some advanced features of the Open vSwitch software switch, read
the `tutorial <Documentation/tutorials/ovs-advanced.rst>`__.
Each Open vSwitch userspace program is accompanied by a manpage. Many of the
manpages are customized to your configuration as part of the build process, so
we recommend building Open vSwitch before reading the manpages.
License
-------
The following is a summary of the licensing of files in this distribution.
As mentioned, Open vSwitch is licensed under the open source Apache 2 license.
Some files may be marked specifically with a different license, in which case
that license applies to the file in question.
Files under the datapath directory are licensed under the GNU General Public
License, version 2.
File build-aux/cccl is licensed under the GNU General Public License, version 2.
The following files are licensed under the 2-clause BSD license.
include/windows/getopt.h
lib/getopt_long.c
lib/conntrack-tcp.c
The following files are licensed under the 3-clause BSD-license
include/windows/netinet/icmp6.h
include/windows/netinet/ip6.h
lib/strsep.c
Files under the xenserver directory are licensed on a file-by-file basis.
Refer to each file for details.
Files lib/sflow*.[ch] are licensed under the terms of either the
Sun Industry Standards Source License 1.1, that is available at:
http://host-sflow.sourceforge.net/sissl.html
or the InMon sFlow License, that is available at:
http://www.inmon.com/technology/sflowlicense.txt
Contact
-------
bugs@openvswitch.org