tc-ets(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | ALGORITHM | CLASSIFICATION | PARAMETERS | EXAMPLE & USAGE | SEE ALSO | AUTHOR | COLOPHON

TC(8)                               Linux                              TC(8)

NAME         top

       ETS - Enhanced Transmission Selection scheduler

SYNOPSIS         top

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

       tc class ... ets [ quantum bytes ]

DESCRIPTION         top

       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         top

       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         top

       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         top

       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         top

       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         top

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

AUTHOR         top

       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.

COLOPHON         top

       This page is part of the iproute2 (utilities for controlling TCP/IP
       networking and traffic) project.  Information about the project can
       be found at 
       ⟨http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2⟩.
       If you have a bug report for this manual page, send it to
       netdev@vger.kernel.org, shemminger@osdl.org.  This page was obtained
       from the project's upstream Git repository
       ⟨https://git.kernel.org/pub/scm/network/iproute2/iproute2.git⟩ on
       2020-08-13.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-06-24.)  If you discover any
       rendering problems in this HTML version of the page, or you believe
       there is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

iproute2                        December 2019                          TC(8)

Pages that refer to this page: tc(8)