openstack/kolla-ansible
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Merge "add ovs-dpdk docs"

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doc/networking-guide.rst
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@ -221,3 +221,130 @@ containers on network/opendaylight node.
For the source code, please refer to the following link:
https://github.com/openstack/networking-odl
OVS with DPDK
=============
Introduction
------------
Open vSwitch (ovs) is an open source software virtual switch developed
and distributed via openvswitch.org.
The Data Plane Development Kit (dpdk) is a collection of userspace
libraries and tools that facilitate the development of high-performance
userspace networking applications.
As of the ovs 2.2 release, the ovs netdev datapath has supported integration
with dpdk for accelerated userspace networking. As of the pike release
of kolla support for deploying ovs with dpdk (ovs-dpdk) has been added
to kolla ansible. The ovs-dpdk role introduced in the pike release has been
tested on centos 7 and ubuntu 16.04 hosts, however, ubuntu is recommended due
to conflicts with the cgroup configuration created by the default systemd
version shipped with centos 7.
Prerequisites
-------------
DPDK is a high-performance userspace networking library, as such it has
several requirements to function correctly that are not required when
deploying ovs without dpdk.
To function efficiently one of the mechanisms dpdk uses to accelerate
memory access is the utilisation of kernel hugepages. The use of hugepage
memory minimises the chance of a translation lookaside buffer(TLB) miss when
translating virtual to physical memory as it increases the total amount of
addressable memory that can be cached via the TLB. Hugepage memory pages are
unswappable contiguous blocks of memory of typically 2MiB or 1GiB in size,
that can be used to facilitate efficient sharing of memory between guests and
a vSwitch or DMA mapping between physical nics and the userspace ovs datapath.
To deploy ovs-dpdk on a platform a proportion of system memory should
be allocated hugepages. While it is possible to allocate hugepages at runtime
it is advised to allocate them via the kernel command line instead to prevent
memory fragmentation. This can be achieved by adding the following to the grub
config and regenerating your grub file.
::
default_hugepagesz=2M hugepagesz=2M hugepages=25000
As dpdk is a userspace networking library it requires userspace compatible
drivers to be able to control the physical interfaces on the platform.
dpdk technically support 3 kernel drivers igb_uio,uio_pci_generic and vfio_pci.
While it is technically possible to use all 3 only uio_pci_generic and vfio_pci
are recommended for use with kolla. igb_uio is BSD licenced and distributed
as part of the dpdk library. While it has some advantages over uio_pci_generic
loading the igb_uio module will taint the kernel and possibly invalidate
distro support. To successfully deploy ovs-dpdk, vfio_pci or uio_pci_generic
kernel module must be present on the platform. Most distros include vfio_pci
or uio_pci_generic as part of the default kernel though on some distros you
may need to install kernel-modules-extra or the distro equivalent prior to
running kolla-ansible deploy.
Install
-------
To enable ovs-dpdk add the following to /etc/kolla/globals.yml
::
ovs_datapath: "netdev"
enable_ovs_dpdk: yes
enable_openvswitch: yes
tunnel_interface: "dpdk_bridge"
neutron_bridge_name: "dpdk_bridge"
Unlike standard Open vSwitch deployments, the interface specified by
neutron_external_interface should have an ip address assigned.
The ip address assigned to neutron_external_interface will be moved to
the "dpdk_bridge" as part of deploy action.
When using ovs-dpdk the tunnel_interface must be an ovs bridge with a physical
interfaces attached for tunnelled traffic to be accelerated by dpdk.
Note that due to a limitation in ansible variable names which excluded
the use of - in a variable name it is not possible to use the default
br-ex name for the neutron_bridge_name or tunnel_interface.
At present, the tunnel interface ip is configured using network manager on
on ubuntu and systemd on centos family operating systems. systemd is used
to work around a limitation of the centos network manager implementation which
does not consider the creation of an ovs bridge to be a hotplug event. In
the future, a new config option will be introduced to allow systemd to be used
on all host distros for those who do not wish to enable the network manager
service on ubuntu.
To manage ovs-dpdk the neutron ovs agent must be configured to use
the netdev datapath_type in the ml2.conf. At present this is not automated
and must be set via kolla's external config support. To set the datapath_type
create a file with the following content at
/etc/kolla/config/neutron/ml2_conf.ini
::
[ovs]
datapath_type = netdev
In the future, the requirement to use the external config will be removed by
automatically computing the value of ovs_datapath based on the value of
enable_ovs_dpdk and then using the ovs_datapath variable to template out this
setting in the ml2_conf.ini automatically.
Limitations
-----------
Reconfiguration from kernel ovs to ovs dpdk is currently not supported.
Changing ovs datapaths on a deployed node requires neutron config changes
and libvirt xml changes for all running instances including a hard reboot
of the vm.
When upgrading ovs-dpdk it should be noted that this will always involve
a dataplane outage. Unlike kernel OVS the dataplane for ovs-dpdk executes in
the ovs-vswitchd process. This means the lifetime of the dpdk dataplane is
tied to the lifetime of the ovsdpdk_vswitchd container. As such it is
recommended to always evacuate all vm workloads from a node running ovs-dpdk
prior to upgrading.
On ubuntu network manager is required for tunnel networking.
This requirement will be removed in the future.