HFSC usage on Linux

The first step to setting up an HFSC qdisc involves assigning a qdisc to a network interface, along with optional specification of a default class:

tc qdisc add dev $dev root handle $ID: hfsc [default $classID ]

In the second step, the class hierarchy is constructed with consecutive class additions. tc add class dev $dev parent parentID classid $ID hfsc [ [ rt SC ] [ ls SC ] | [ sc SC ] ] [ ul SC ]

The particular attributes of each class are configured via the service curves which are described as follows: SC := [ umax bytes dmax ms ] rate BPS

Classes at the lowest level of the hierarchy can be assigned a real-time curve (rt) as well as a link-sharing curve (ls), where inner classes can only have a link-sharing curve. By using the ul service curve, an upper limit on service actually rendered to each class can be defined. Instead of specifying two identical rt and ls curves, a single sc curve can be specified. A service curve is described by its transmission rate, which correlates with the slope of the curve. If the curve consists of two parts, it can be specified with dmax the maximum delay at a certain transmission rate umax.

==============================================================

HFSC: What is “sc” ?

SC := [ [ m1 BPS ] [ d SEC ] m2 BPS

m1 : slope of first segment
d : x-coordinate of intersection
m2 : slope of second segment

Alternative format:

SC := [ [ umax BYTE ] dmax SEC ] rate BPS

umax : maximum unit of work
dmax : maximum delay
rate : rate

================================================================