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
       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)