2023.2 Series Release Notes¶

3.2.0¶

A new config option has been added to the OpenvSwitch plugin [os_vif_ovs]default_qos_type. This option controls the Default tc qdisc applied to a kernel interface attached to OpenvSwitch on Linux hosts. As of this release, the default tc qdisc is linux-noop other supported values are linux-htb, linux-hfsc, linux-sfq, linux-codel and linux-fq_codel. before this release the default qdisc was undefined. older kernels did not apply /proc/sys/net/core/default_qdisc to tap devices. newer kernels such as the one found in rhel 9 do. This can significantly impact performance. See bug https://bugs.launchpad.net/os-vif/+bug/2017868 for more details. The default linux-noop should perform well for all use-cases so no explicit action is required on upgrade however it should be noted that the default_qos_type is only set when a port is first created. As such this fix will not take effect until the next time the vm interface is recreated. If you change this value for an existing port it will only take effect after a hard reboot of the VM or a move operation.

A significant performance regression was observed on a subset of Linux kernels and sysctl configurations resulting in a reduction of throughput to between 10% of the prior performance for small packets and 50% for large packets. This has now been resolved by setting a default qos_type on ovs interfaces when they are first created. To mimic libvirt’s undocumented behavior the linux-noop type is set on the ovs port when it is first created. This will be overridden by neutron if a qos policy is defined for a port and is simply the initial value to use when first adding a port to OpenvSwitch. The default QoS type applied can be controlled by the [os_vif_ovs]default_qos_type config operation. See bug https://bugs.launchpad.net/os-vif/+bug/2017868 for more details.