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The 'struct json' contains a union and the largest element of that
union is 'struct json_array', which takes 24 bytes. It means, that a
lot of space in this structure remains unused whenever the type is not
JSON_ARRAY.
For example, the 'string' pointer used for JSON_STRING only takes 8
bytes on a 64-bit system leaving 24 - 8 = 16 bytes unused. There is
also a 4-byte hole between the 'type' and the 'count'.
A pretty common optimization technique for storing strings is to
store short ones in place of the pointer and only allocate dynamically
the larger strings that do not fit. In our case, we have even larger
space of 24 bytes to work with. So, we could use all 24 bytes to
store the strings (23 string bytes + '\0') and use the 4 byte unused
space outside the union to store the storage type.
This approach should allow us to save on memory allocation for short
strings and also save on accesses to them, as the content will fit
into the same cache line as the 'struct json' itself.
In practice, large OVN databases tend to operate with quite large
strings. For example, all the logical flow matches and actions in
OVN Southbound database would not fit. However, this approach still
allows to improve performance with large OVN databases.
With 350MB OVN Northbound database with 12M atoms:
Before After Improvement
ovsdb-client dump 18.6 sec 16.6 sec 10.7 %
Compaction 14.0 sec 13.4 sec 4.2 %
Memory usage (RSS) 2.28 GB 2.05 GB 10.0 %
With 615MB OVN Southbound database with 23M atoms:
Before After Improvement
ovsdb-client dump 46.1 sec 43.7 sec 5.2 %
Compaction 34.8 sec 32.5 sec 6.6 %
Memory usage (RSS) 5.29 GB 4.80 GB 9.3 %
In the results above, 'ovsdb-client dump' is measuring how log it
takes for the server to prepare and send a reply, 'Memory usage (RSS)'
reflects the RSS of the ovsdb-server after loading the full database.
ovn-heater tests report similar reduction in CPU and memory usage
on heavy operations like compaction.
Acked-by: Mike Pattrick <mkp@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
.. 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://github.com/openvswitch/ovs/workflows/Build%20and%20Test/badge.svg
:target: https://github.com/openvswitch/ovs/actions
.. image:: https://ci.appveyor.com/api/projects/status/github/openvswitch/ovs?branch=main&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
.. image:: https://readthedocs.org/projects/openvswitch/badge/?version=latest
:target: https://docs.openvswitch.org/en/latest/
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 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, ERSPAN, GTP-U, SRv6, and Bareudp 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
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 Red Hat Enterprise Linux and
deb packages for Ubuntu/Debian.
- 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 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