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d2773f1261
Add a new module to generate and parse options specific to the ETS Qdisc.
Example output:
bands 8 strict 3 priomap 0 1 2 3 4 5 6 7
qdisc ets 1: root refcnt 2 offloaded bands 8 strict 3 quanta 1514 1514 1514 1514 1514 priomap 0 1 2 3 4 5 6 7 7 7 7 7 7 7 7 7
[
{
"kind": "ets",
"handle": "1:",
"root": true,
"refcnt": 2,
"offloaded": true,
"options": {
"bands": 8,
"strict": 3,
"quanta": [1514, 1514, 1514, 1514, 1514],
"priomap": [0, 1, 2, 3, 4, 5, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7]
}
}
]
Signed-off-by: Petr Machata <petrm@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David Ahern <dsahern@gmail.com>
193 lines
6.5 KiB
Groff
193 lines
6.5 KiB
Groff
.TH TC 8 "December 2019" "iproute2" "Linux"
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.SH NAME
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ETS \- Enhanced Transmission Selection scheduler
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.SH SYNOPSIS
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.B tc qdisc ... ets [ bands
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number
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.B ] [ strict
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number
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.B ] [ quanta
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bytes bytes bytes...
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.B ] [ priomap
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band band band...
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.B ]
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.B tc class ... ets [ quantum
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bytes
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.B ]
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.SH DESCRIPTION
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The Enhanced Transmission Selection scheduler is a classful queuing
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discipline that merges functionality of PRIO and DRR qdiscs in one
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scheduler. ETS makes it easy to configure a set of strict and
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bandwidth-sharing bands to implement the transmission selection described
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in 802.1Qaz.
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On creation with 'tc qdisc add', a fixed number of bands is created. Each
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band is a class, although it is not possible to directly add and remove
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bands with 'tc class' commands. The number of bands to be created must
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instead be specified on the command line as the qdisc is added.
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The minor number of classid to use when referring to a band is the band
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number increased by one. Thus band 0 will have classid of major:1, band 1
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that of major:2, etc.
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ETS bands are of two types: some number may be in strict mode, the
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remaining ones are in bandwidth-sharing mode.
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.SH ALGORITHM
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When dequeuing, strict bands are tried first, if there are any. Band 0 is
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tried first. If it did not deliver a packet, band 1 is tried next, and so
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on until one of the bands delivers a packet, or the strict bands are
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exhausted.
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If no packet has been dequeued from any of the strict bands, if there are
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any bandwidth-sharing bands, the dequeuing proceeds according to the DRR
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algorithm. Each bandwidth-sharing band is assigned a deficit counter,
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initialized to quantum assigned by a
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.B quanta
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element. ETS maintains an (internal) ''active'' list of bandwidth-sharing
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bands whose qdiscs are non-empty. This list is used for dequeuing. A packet
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is dequeued from the band at the head of the list if the packet size is
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smaller or equal to the deficit counter. If the counter is too small, it is
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increased by
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.B quantum
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and the scheduler moves on to the next band in the active list.
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Only qdiscs that own their queue should be added below the
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bandwidth-sharing bands. Attaching to them non-work-conserving qdiscs like
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TBF does not make sense \-\- other qdiscs in the active list will be
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skipped until the dequeue operation succeeds. This limitation does not
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exist with the strict bands.
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.SH CLASSIFICATION
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The ETS qdisc allows three ways to decide which band to enqueue a packet
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to:
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- Packet priority can be directly set to a class handle, in which case that
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is the queue where the packet will be put. For example, band number 2 of
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a qdisc with handle of 11: will have classid 11:3. To mark a packet for
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queuing to this band, the packet priority should be set to 0x110003.
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- A tc filter attached to the qdisc can put the packet to a band by using
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the \fBflowid\fR keyword.
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- As a last resort, the ETS qdisc consults its priomap (see below), which
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maps packets to bands based on packet priority.
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.SH PARAMETERS
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.TP
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strict
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The number of bands that should be created in strict mode. If not given,
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this value is 0.
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.TP
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quanta
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Each bandwidth-sharing band needs to know its quantum, which is the amount
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of bytes a band is allowed to dequeue before the scheduler moves to the
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next bandwidth-sharing band. The
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.B quanta
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argument lists quanta for the individual bandwidth-sharing bands.
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The minimum value of each quantum is 1. If
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.B quanta
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is not given, the default is no bandwidth-sharing bands, but note that when
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specifying a large number of
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.B bands,
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the extra ones are in bandwidth-sharing mode by default.
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.TP
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bands
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Number of bands given explicitly. This value has to be at least large
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enough to cover the strict bands specified through the
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.B strict
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keyword and bandwidth-sharing bands specified in
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.B quanta.
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If a larger value is given, any extra bands are in bandwidth-sharing mode,
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and their quanta are deduced from the interface MTU. If no value is given,
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as many bands are created as necessary to cover all bands implied by the
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.B strict
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and
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.B quanta
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keywords.
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.TP
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priomap
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The priomap maps the priority of a packet to a band. The argument is a list
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of numbers. The first number indicates which band the packets with priority
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0 should be put to, the second is for priority 1, and so on.
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There can be up to 16 numbers in the list. If there are fewer, the default
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band that traffic with one of the unmentioned priorities goes to is the
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last one.
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.SH EXAMPLE & USAGE
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.P
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Add a qdisc with 8 bandwidth-sharing bands, using the interface MTU as
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their quanta. Since all quanta are the same, this will lead to equal
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distribution of bandwidth between the bands, each will get about 12.5% of
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the link. The low 8 priorities go to individual bands in a reverse 1:1
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fashion (such that the highest priority goes to the first band).
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.P
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# tc qdisc add dev eth0 root handle 1: ets bands 8 priomap 7 6 5 4 3 2 1 0
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.br
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# tc qdisc show dev eth0
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.br
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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
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.P
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Tweak the first band of the above qdisc to give it a quantum of 2650, which
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will give it about 20% of the link (and about 11.5% to the remaining
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bands):
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.P
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# tc class change dev eth0 classid 1:1 ets quantum 2650
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.br
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# tc qdisc show dev eth0
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.br
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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
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.P
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Create a purely strict Qdisc with reverse 1:1 mapping between priorities
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and bands:
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.P
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# tc qdisc add dev eth0 root handle 1: ets strict 8 priomap 7 6 5 4 3 2 1 0
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.br
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# tc qdisc sh dev eth0
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.br
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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
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.P
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Add a Qdisc with 6 bands, 3 strict and 3 ETS with 35%-30%-25% weights:
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.P
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# tc qdisc add dev eth0 root handle 1: ets strict 3 quanta 3500 3000 2500 priomap 0 1 1 1 2 3 4 5
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.br
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# tc qdisc sh dev eth0
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.br
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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
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.P
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Create a Qdisc such that traffic with priorities 2, 3 and 4 are strictly
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prioritized over other traffic, and the rest goes into bandwidth-sharing
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classes with equal weights:
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.P
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# tc qdisc add dev eth0 root handle 1: ets bands 8 strict 3 priomap 3 4 0 1 2 5 6 7
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.br
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# tc qdisc sh dev eth0
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.br
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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
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.SH SEE ALSO
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.BR tc (8),
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.BR tc-prio (8),
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.BR tc-drr (8)
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.SH AUTHOR
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Parts of both this manual page and the code itself are taken from PRIO and
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DRR qdiscs.
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.br
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ETS qdisc itself was written by Petr Machata.
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