tc-prio

tc qdisc add dev dev parent parentid handle handleid prio
[ bands number ] [ priomap prio_map ]

dev dev
    Specifies the network interface the qdisc is attached to. dev is the name of the network interface (e.g., eth0, enp0s3).

parent parentid
    Specifies the parent of this qdisc. Can be root (to attach directly to the interface) or another qdisc's handle. For example, parent 1: or parent root.

handle handleid
    Assigns a handle to the qdisc, which is used to refer to it later. Handles are typically represented as a major:minor pair (e.g., 1: or 10:).

prio
    Indicates that the prio queuing discipline is being used.

bands number
    Specifies the number of bands or priority levels. Defaults to 3.
The maximum is limited by the priomap setting, but it is good practice to make it a power of 2.

priomap prio_map
    Defines the mapping between the packet priority and the bands. The prio_map is a comma separated list of up to 16 numbers that specifies which band each priority maps to. By default is 0,1,2,2,1,0,2,2 mapping.

The tc-prio command is part of the tc (traffic control) suite in Linux. It's used to configure the prio (priority) queuing discipline (qdisc). The prio qdisc allows you to create multiple bands or traffic classes (typically three or more) with differing priorities. Packets are then enqueued into the appropriate band based on rules you define, and the scheduler always tries to dequeue from the highest priority band first. This allows you to prioritize certain types of traffic, such as interactive applications or VoIP, over less sensitive traffic like bulk data transfers. Using tc-prio enables Quality of Service (QoS) by ensuring critical data receives preferential treatment during periods of network congestion.

Incorrectly configured prio qdiscs can lead to starvation of lower-priority traffic. Care must be taken when mapping traffic priorities to bands.

Each band under the prio qdisc requires a child qdisc. Typically, these child qdiscs are simple leaf qdiscs like pfifo_fast or more complex shaping qdiscs. These child qdiscs are attached using tc filter rules that classify traffic into the appropriate band based on various criteria like IP address, port number, or protocol.

tc filter rules are essential to assign packets to the correct priority band. These filters examine packet headers and use criteria like protocol, source/destination IP addresses and ports, or TOS/DSCP values to determine the appropriate band. Without effective traffic classification, the prio qdisc cannot properly prioritize traffic.

The tc command and the associated queuing disciplines, including prio, have been part of the Linux kernel for many years as the primary mechanism for traffic control. Development has been ongoing to improve QoS capabilities and adapt to evolving network requirements. The prio qdisc has been a fundamental building block for creating prioritized traffic shaping configurations.

tc(8), tc-fq_codel(8), tc-htb(8)