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NAME | SYNOPSIS | DESCRIPTION | ALGORITHM | CLASSIFICATION | PARAMETERS | EXAMPLE & USAGE | SEE ALSO | AUTHOR | COLOPHON |
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TC(8) Linux TC(8)
ETS - Enhanced Transmission Selection scheduler
tc qdisc ... ets [ bands number ] [ strict number ] [ quanta bytes
bytes bytes... ] [ priomap band band band... ]
tc class ... ets [ quantum bytes ]
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.
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.
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.
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.
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
tc(8), tc-prio(8), tc-drr(8)
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.
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
2025-02-02. (At that time, the date of the most recent commit
that was found in the repository was 2025-01-21.) 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)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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