add ovs-dpdk docs
- This change extends the networking-guide to describe how to enable the newly added support for deploying ovs-dpdk. Change-Id: I43405760ff315497f9396bfb0b36d6aa7fc5462a Partially-Implements: blueprint ovs-dpdk
This commit is contained in:
Sean Mooney
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0a1e7f6d86
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05b4ac1a59
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@ -221,3 +221,130 @@ containers on network/opendaylight node.
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For the source code, please refer to the following link:
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https://github.com/openstack/networking-odl
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OVS with DPDK
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=============
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Introduction
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------------
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Open vSwitch (ovs) is an open source software virtual switch developed
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and distributed via openvswitch.org.
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The Data Plane Development Kit (dpdk) is a collection of userspace
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libraries and tools that facilitate the development of high-performance
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userspace networking applications.
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As of the ovs 2.2 release, the ovs netdev datapath has supported integration
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with dpdk for accelerated userspace networking. As of the pike release
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of kolla support for deploying ovs with dpdk (ovs-dpdk) has been added
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to kolla ansible. The ovs-dpdk role introduced in the pike release has been
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tested on centos 7 and ubuntu 16.04 hosts, however, ubuntu is recommended due
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to conflicts with the cgroup configuration created by the default systemd
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version shipped with centos 7.
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Prerequisites
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-------------
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DPDK is a high-performance userspace networking library, as such it has
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several requirements to function correctly that are not required when
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deploying ovs without dpdk.
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To function efficiently one of the mechanisms dpdk uses to accelerate
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memory access is the utilisation of kernel hugepages. The use of hugepage
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memory minimises the chance of a translation lookaside buffer(TLB) miss when
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translating virtual to physical memory as it increases the total amount of
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addressable memory that can be cached via the TLB. Hugepage memory pages are
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unswappable contiguous blocks of memory of typically 2MiB or 1GiB in size,
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that can be used to facilitate efficient sharing of memory between guests and
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a vSwitch or DMA mapping between physical nics and the userspace ovs datapath.
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To deploy ovs-dpdk on a platform a proportion of system memory should
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be allocated hugepages. While it is possible to allocate hugepages at runtime
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it is advised to allocate them via the kernel command line instead to prevent
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memory fragmentation. This can be achieved by adding the following to the grub
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config and regenerating your grub file.
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::
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default_hugepagesz=2M hugepagesz=2M hugepages=25000
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As dpdk is a userspace networking library it requires userspace compatible
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drivers to be able to control the physical interfaces on the platform.
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dpdk technically support 3 kernel drivers igb_uio,uio_pci_generic and vfio_pci.
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While it is technically possible to use all 3 only uio_pci_generic and vfio_pci
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are recommended for use with kolla. igb_uio is BSD licenced and distributed
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as part of the dpdk library. While it has some advantages over uio_pci_generic
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loading the igb_uio module will taint the kernel and possibly invalidate
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distro support. To successfully deploy ovs-dpdk, vfio_pci or uio_pci_generic
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kernel module must be present on the platform. Most distros include vfio_pci
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or uio_pci_generic as part of the default kernel though on some distros you
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may need to install kernel-modules-extra or the distro equivalent prior to
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running kolla-ansible deploy.
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Install
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-------
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To enable ovs-dpdk add the following to /etc/kolla/globals.yml
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::
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ovs_datapath: "netdev"
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enable_ovs_dpdk: yes
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enable_openvswitch: yes
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tunnel_interface: "dpdk_bridge"
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neutron_bridge_name: "dpdk_bridge"
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Unlike standard Open vSwitch deployments, the interface specified by
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neutron_external_interface should have an ip address assigned.
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The ip address assigned to neutron_external_interface will be moved to
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the "dpdk_bridge" as part of deploy action.
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When using ovs-dpdk the tunnel_interface must be an ovs bridge with a physical
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interfaces attached for tunnelled traffic to be accelerated by dpdk.
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Note that due to a limitation in ansible variable names which excluded
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the use of - in a variable name it is not possible to use the default
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br-ex name for the neutron_bridge_name or tunnel_interface.
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At present, the tunnel interface ip is configured using network manager on
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on ubuntu and systemd on centos family operating systems. systemd is used
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to work around a limitation of the centos network manager implementation which
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does not consider the creation of an ovs bridge to be a hotplug event. In
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the future, a new config option will be introduced to allow systemd to be used
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on all host distros for those who do not wish to enable the network manager
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service on ubuntu.
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To manage ovs-dpdk the neutron ovs agent must be configured to use
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the netdev datapath_type in the ml2.conf. At present this is not automated
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and must be set via kolla's external config support. To set the datapath_type
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create a file with the following content at
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/etc/kolla/config/neutron/ml2_conf.ini
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::
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[ovs]
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datapath_type = netdev
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In the future, the requirement to use the external config will be removed by
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automatically computing the value of ovs_datapath based on the value of
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enable_ovs_dpdk and then using the ovs_datapath variable to template out this
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setting in the ml2_conf.ini automatically.
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Limitations
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-----------
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Reconfiguration from kernel ovs to ovs dpdk is currently not supported.
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Changing ovs datapaths on a deployed node requires neutron config changes
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and libvirt xml changes for all running instances including a hard reboot
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of the vm.
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When upgrading ovs-dpdk it should be noted that this will always involve
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a dataplane outage. Unlike kernel OVS the dataplane for ovs-dpdk executes in
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the ovs-vswitchd process. This means the lifetime of the dpdk dataplane is
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tied to the lifetime of the ovsdpdk_vswitchd container. As such it is
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recommended to always evacuate all vm workloads from a node running ovs-dpdk
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prior to upgrading.
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On ubuntu network manager is required for tunnel networking.
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This requirement will be removed in the future.
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