Configuring Network QoS Parameters
You can use the OpenStack Nova command-line interface (CLI)
to specify a quality of service (QoS) setting for a virtual machine’s
network interface, by setting the
quota of a Nova flavor. Any virtual machine created with that Nova flavor
will inherit all of the specified QoS settings. Additionally, if the
virtual machine that was created with the QoS settings has multiple
interfaces in different virtual networks, the same QoS settings will
be applied to all of the network interfaces associated with the virtual
machine. The QoS settings can be specified in unidirectional or bidirectional
quota driver in Neutron converts
QoS parameters into
libvirt network settings
of the virtual machine.
The QoS parameters available in the quota driver only cover rate limiting the network interface. There are no specifications available for policy-based QoS at this time.
QoS Configuration Examples
Although the QoS setting can be specified in quota by using either Horizon or CLI, quota creation using CLI is more robust and stable, therefore, creating by CLI is the recommended method.
CLI for Nova flavor has the following format:
nova flavor-key <flavor_name> set quota:vif_<direction> _<param_name> = value
<flavor_name> is the name of an existing Nova flavor.
vif_<direction>_<param_name> is the inbound or outbound
QoS data name.
vif types include the following:
vif_inbound_averagelets you specify the average rate of inbound (receive) traffic, in kilobytes/sec.
vif_outbound_averagelets you specify the average rate of outbound (transmit) traffic, in kilobytes/sec.
vif_outbound_peakspecify the maximum rate of inbound and outbound traffic, respectively, in kilobytes/sec.
vif_outbound_peakspecify the amount of kilobytes that can be received or transmitted, respectively, in a single burst at the peak rate.
Details for various QoS parameters for
libvirt can be found at http://libvirt.org/formatnetwork.html.
The following example shows an inbound average of 800 kilobytes/sec, a peak of 1000 kilobytes/sec, and a burst amount of 30 kilobytes.
nova flavor-key m1.small set quota:vif_inbound_average=800 nova flavor-key m1.small set quota:vif_inbound_peak=1000 nova flavor-key m1.small set quota:vif_inbound_burst=30
The following is an example of specified outbound parameters:
nova flavor-key m1.small set quota:vif_outbound_average=800 nova flavor-key m1.small set quota:vif_outbound_peak=1000 nova flavor-key m1.small set quota:vif_outbound_burst=30
After the Nova flavor is configured for QoS, a virtual machine instance can be created, using either Horizon or CLI. The instance will have network settings corresponding to the nova flavor-key, as in the following:
<interface type="ethernet"> <mac address="02:a3:a0:87:7f:61"/> <model type="virtio"/> <script path=""/> <target dev="tapa3a0877f-61"/> <bandwidth> <inbound average="800" peak="1000" burst="30"/> <outbound average="800" peak="1000" burst="30"/> </bandwidth> </interface>
libvirtdoes not support rate limiting of
ethernetinterface types. Consequently, settings like those in the example for the guest interface will not result in any
tc qdiscsettings for the corresponding tap device in the host.
nova flavor-key rxtx_factortakes a float as an input and acts as a scaling factor for receive (inbound) and transmit (outbound) throughputs. This key is only available to Neutron extensions (private extensions). The Contrail Neutron plugin doesn’t implement this private extension. Consequently, setting the
nova flavor-key rxtx_factorwill not have any effect on the QoS setting of the network interface(s) of any virtual machine created with that nova flavor.
The outbound rate limits of a virtual machine interface are not strictly achieved. The outbound throughput of a virtual machine network interface is always less than the average outbound limit specified in the virtual machine's libvirt configuration file. The same behavior is also seen when using a Linux bridge.