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+.TH TC 8 "December 2019" "iproute2" "Linux"
+.SH NAME
+ETS \- Enhanced Transmission Selection scheduler
+.SH SYNOPSIS
+.B tc qdisc ... ets [ bands
+number
+.B ] [ strict
+number
+.B ] [ quanta
+bytes bytes bytes...
+.B ] [ priomap
+band band band...
+.B ]
+
+.B tc class ... ets [ quantum
+bytes
+.B ]
+
+.SH 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.
+
+.SH 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
+.B 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
+.B 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.
+
+.SH 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 \fBflowid\fR keyword.
+
+- As a last resort, the ETS qdisc consults its priomap (see below), which
+  maps packets to bands based on packet priority.
+
+.SH PARAMETERS
+.TP
+strict
+The number of bands that should be created in strict mode. If not given,
+this value is 0.
+
+.TP
+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
+.B quanta
+argument lists quanta for the individual bandwidth-sharing bands.
+The minimum value of each quantum is 1. If
+.B quanta
+is not given, the default is no bandwidth-sharing bands, but note that when
+specifying a large number of
+.B bands,
+the extra ones are in bandwidth-sharing mode by default.
+
+.TP
+bands
+Number of bands given explicitly. This value has to be at least large
+enough to cover the strict bands specified through the
+.B strict
+keyword and bandwidth-sharing bands specified in
+.B 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
+.B strict
+and
+.B quanta
+keywords.
+
+.TP
+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.
+
+.SH EXAMPLE & USAGE
+
+.P
+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).
+
+.P
+# tc qdisc add dev eth0 root handle 1: ets bands 8 priomap 7 6 5 4 3 2 1 0
+.br
+# tc qdisc show dev eth0
+.br
+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
+
+.P
+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):
+
+.P
+# tc class change dev eth0 classid 1:1 ets quantum 2650
+.br
+# tc qdisc show dev eth0
+.br
+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
+
+.P
+Create a purely strict Qdisc with reverse 1:1 mapping between priorities
+and bands:
+
+.P
+# tc qdisc add dev eth0 root handle 1: ets strict 8 priomap 7 6 5 4 3 2 1 0
+.br
+# tc qdisc sh dev eth0
+.br
+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
+
+.P
+Add a Qdisc with 6 bands, 3 strict and 3 ETS with 35%-30%-25% weights:
+.P
+# tc qdisc add dev eth0 root handle 1: ets strict 3 quanta 3500 3000 2500 priomap 0 1 1 1 2 3 4 5
+.br
+# tc qdisc sh dev eth0
+.br
+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
+
+.P
+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:
+.P
+# tc qdisc add dev eth0 root handle 1: ets bands 8 strict 3 priomap 3 4 0 1 2 5 6 7
+.br
+# tc qdisc sh dev eth0
+.br
+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
+
+.SH SEE ALSO
+.BR tc (8),
+.BR tc-prio (8),
+.BR tc-drr (8)
+
+.SH AUTHOR
+Parts of both this manual page and the code itself are taken from PRIO and
+DRR qdiscs.
+.br
+ETS qdisc itself was written by Petr Machata.