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 bandwidth-
       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 created
       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 remaining 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 maintains an (internal) ''active'' list
       of  bandwidth-sharing  bands  whose  qdiscs  are  non-empty. This list is used for dequeuing. A packet is
       dequeued 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 using
         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 necessary to cover  all
              bands implied by the strict and quanta keywords.

       priomap
              The  priomap maps the priority of a packet to a band. The argument 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 priorities 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 remaining 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 priorities 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 priomap 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 bandwidth-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)