ets(8)



TC(8)                                Linux                               TC(8)

NAME
       ETS - Enhanced Transmission Selection scheduler

SYNOPSIS
       tc  qdisc  ...  ets  [  bands number ] [ strict number ] [ quanta bytes
       bytes bytes...  ] [ priomap band band band...  ]

       tc class ... ets [ quantum bytes ]

DESCRIPTION
       The Enhanced Transmission Selection scheduler  is  a  classful  queuing
       discipline  that  merges  functionality  of  PRIO and DRR qdiscs in one
       scheduler. ETS makes it easy to configure a set  of  strict  and  band-
       width-sharing  bands  to implement the transmission selection described
       in 802.1Qaz.

       On creation with 'tc qdisc add', a fixed number of  bands  is  created.
       Each  band  is a class, although it is not possible to directly add and
       remove bands with 'tc class' commands. The number of bands to  be  cre-
       ated  must  instead  be  specified  on the command line as the qdisc is
       added.

       The minor number of classid to use when referring to a band is the band
       number increased by one. Thus band 0 will have classid of major:1, band
       1 that of major:2, etc.

       ETS bands are of two types: some number may be in strict mode, the  re-
       maining ones are in bandwidth-sharing mode.

ALGORITHM
       When  dequeuing, strict bands are tried first, if there are any. Band 0
       is tried first. If it did not deliver a packet, band 1 is  tried  next,
       and so on until one of the bands delivers a packet, or the strict bands
       are exhausted.

       If no packet has been dequeued from any of the strict bands,  if  there
       are  any  bandwidth-sharing  bands, the dequeuing proceeds according to
       the DRR algorithm. Each bandwidth-sharing band is  assigned  a  deficit
       counter, initialized to quantum assigned by a quanta element. ETS main-
       tains an (internal) ''active'' list of  bandwidth-sharing  bands  whose
       qdiscs  are non-empty. This list is used for dequeuing. A packet is de-
       queued from the band at the head of the list  if  the  packet  size  is
       smaller  or  equal to the deficit counter. If the counter is too small,
       it is increased by quantum and the scheduler moves on to the next  band
       in the active list.

       Only  qdiscs  that own their queue should be added below the bandwidth-
       sharing bands. Attaching to them non-work-conserving  qdiscs  like  TBF
       does  not make sense -- other qdiscs in the active list will be skipped
       until the dequeue operation succeeds. This limitation  does  not  exist
       with the strict bands.

CLASSIFICATION
       The  ETS  qdisc  allows  three  ways  to decide which band to enqueue a
       packet to:

       - Packet priority can be directly set to a class handle, in which  case
       that
         is the queue where the packet will be put. For example, band number 2
       of
         a qdisc with handle of 11: will have classid 11:3. To mark  a  packet
       for
         queuing to this band, the packet priority should be set to 0x110003.

       - A tc filter attached to the qdisc can put the packet to a band by us-
       ing
         the flowid keyword.

       - As a last resort, the ETS qdisc consults  its  priomap  (see  below),
       which
         maps packets to bands based on packet priority.

PARAMETERS
       strict The  number  of  bands that should be created in strict mode. If
              not given, this value is 0.

       quanta Each bandwidth-sharing band needs to know its quantum, which  is
              the  amount  of  bytes  a  band is allowed to dequeue before the
              scheduler moves to the next bandwidth-sharing band.  The  quanta
              argument  lists  quanta  for  the  individual  bandwidth-sharing
              bands.  The minimum value of each quantum is 1. If quanta is not
              given,  the default is no bandwidth-sharing bands, but note that
              when specifying a large number of bands, the extra ones  are  in
              bandwidth-sharing mode by default.

       bands  Number  of bands given explicitly. This value has to be at least
              large enough to cover the strict  bands  specified  through  the
              strict  keyword and bandwidth-sharing bands specified in quanta.
              If a larger value is given, any extra bands  are  in  bandwidth-
              sharing  mode,  and  their quanta are deduced from the interface
              MTU. If no value is given, as many bands are created  as  neces-
              sary  to  cover  all bands implied by the strict and quanta key-
              words.

       priomap
              The priomap maps the priority of a packet to a band.  The  argu-
              ment is a list of numbers. The first number indicates which band
              the packets with priority 0 should be put to, the second is  for
              priority 1, and so on.

              There  can  be up to 16 numbers in the list. If there are fewer,
              the default band that traffic with one of the unmentioned prior-
              ities goes to is the last one.

EXAMPLE & USAGE
       Add  a qdisc with 8 bandwidth-sharing bands, using the interface MTU as
       their quanta. Since all quanta are the same, this will  lead  to  equal
       distribution  of bandwidth between the bands, each will get about 12.5%
       of the link. The low 8 priorities go to individual bands in  a  reverse
       1:1 fashion (such that the highest priority goes to the first band).

       #  tc qdisc add dev eth0 root handle 1: ets bands 8 priomap 7 6 5 4 3 2
       1 0
       # tc qdisc show dev eth0
       qdisc ets 1: root refcnt 2 bands 8 quanta 1514 1514 1514 1514 1514 1514
       1514 1514 priomap 7 6 5 4 3 2 1 0 7 7 7 7 7 7 7 7

       Tweak  the  first band of the above qdisc to give it a quantum of 2650,
       which will give it about 20% of the link (and about 11.5%  to  the  re-
       maining bands):

       # tc class change dev eth0 classid 1:1 ets quantum 2650
       # tc qdisc show dev eth0
       qdisc ets 1: root refcnt 2 bands 8 quanta 2650 1514 1514 1514 1514 1514
       1514 1514 priomap 7 6 5 4 3 2 1 0 7 7 7 7 7 7 7 7

       Create a purely strict Qdisc with reverse 1:1 mapping  between  priori-
       ties and bands:

       # tc qdisc add dev eth0 root handle 1: ets strict 8 priomap 7 6 5 4 3 2
       1 0
       # tc qdisc sh dev eth0
       qdisc ets 1: root refcnt 2 bands 8 strict 8 priomap 7 6 5 4 3 2 1 0 7 7
       7 7 7 7 7 7

       Add a Qdisc with 6 bands, 3 strict and 3 ETS with 35%-30%-25% weights:

       #  tc  qdisc  add dev eth0 root handle 1: ets strict 3 quanta 3500 3000
       2500 priomap 0 1 1 1 2 3 4 5
       # tc qdisc sh dev eth0
       qdisc ets 1: root refcnt 2 bands 6 strict 3 quanta 3500 3000 2500  pri-
       omap 0 1 1 1 2 3 4 5 5 5 5 5 5 5 5 5

       Create  a  Qdisc  such  that  traffic  with  priorities  2, 3 and 4 are
       strictly prioritized over other traffic, and the rest goes  into  band-
       width-sharing classes with equal weights:

       # tc qdisc add dev eth0 root handle 1: ets bands 8 strict 3 priomap 3 4
       0 1 2 5 6 7
       # tc qdisc sh dev eth0
       qdisc ets 1: root refcnt 2 bands 8 strict 3 quanta 1514 1514 1514  1514
       1514 priomap 3 4 0 1 2 5 6 7 7 7 7 7 7 7 7 7

SEE ALSO
       tc(8), tc-prio(8), tc-drr(8)

AUTHOR
       Parts  of both this manual page and the code itself are taken from PRIO
       and DRR qdiscs.
       ETS qdisc itself was written by Petr Machata.

iproute2                         December 2019                           TC(8)

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