.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.