HFSC(8)                             Linux                            HFSC(8)

NAME         top

       HFSC - Hierarchical Fair Service Curve's control under linux

SYNOPSIS         top

       tc qdisc add ... hfsc [ default CLASSID ]

       tc class add ... hfsc [ [ rt SC ] [ ls SC ] | [ sc SC ] ] [ ul SC ]

       rt : realtime service curve
       ls : linkshare service curve
       sc : rt+ls service curve
       ul : upperlimit service curve

       · at least one of rt, ls or sc must be specified
       · ul can only be specified with ls or sc

       SC := [ [ m1 BPS ] d SEC ] m2 BPS
              m1 : slope of the first segment
              d  : x-coordinate of intersection
              m2 : slope of the second segment

       SC := [ [ umax BYTE ] dmax SEC ] rate BPS
              umax : maximum unit of work
              dmax : maximum delay
              rate : rate

       For description of BYTE, BPS and SEC - please see UNITS section of

DESCRIPTION (qdisc)         top

       HFSC qdisc has only one optional parameter - default. CLASSID
       specifies the minor part of the default classid, where packets not
       classified by other means (e.g. u32 filter, CLASSIFY target of
       iptables) will be enqueued. If default is not specified, unclassified
       packets will be dropped.

DESCRIPTION (class)         top

       HFSC class is used to create a class hierarchy for HFSC scheduler.
       For explanation of the algorithm, and the meaning behind rt, ls, sc
       and ul service curves - please refer to tc-hfsc(7).

       As you can see in SYNOPSIS, service curve (SC) can be specified in
       two ways. Either as maximum delay for certain amount of work, or as a
       bandwidth assigned for certain amount of time. Obviously, m1 is
       simply umax/dmax.

       Both m2 and rate are mandatory. If you omit other parameters, you
       will specify linear service curve.

SEE ALSO         top

       tc(8), tc-hfsc(7), tc-stab(8)

       Please direct bugreports and patches to: <>

AUTHOR         top

       Manpage created by Michal Soltys (

COLOPHON         top

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iproute2                       31 October 2011                       HFSC(8)