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

       o at least one of rt, ls or sc must be specified
       o 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

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

       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 band-
       width assigned for certain amount of  time.  Obviously,  m1  is  simply

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

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

       Please direct bugreports and patches to: <>

       Manpage created by Michal Soltys (
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