.TH MQPRIO 8 "24 Sept 2013" "iproute2" "Linux"

.SH NAME

MQPRIO \- Multiqueue Priority Qdisc (Offloaded Hardware QOS)

.SH SYNOPSIS

.B tc qdisc ... dev

dev

.B  ( parent

classid

.B | root) [ handle

major:

.B ] mqprio [ num_tc

tcs

.B ] [ map

P0 P1 P2...

.B ] [ queues

count1@offset1 count2@offset2 ...

.B ] [ hw

1|0

.B ] [ mode

dcb|channel]

.B ] [ shaper

dcb|

.B [ bw_rlimit

.B min_rate

min_rate1 min_rate2 ...

.B max_rate

max_rate1 max_rate2 ...

.B ]]

.SH DESCRIPTION

The MQPRIO qdisc is a simple queuing discipline that allows mapping

traffic flows to hardware queue ranges using priorities and a configurable

priority to traffic class mapping. A traffic class in this context is

a set of contiguous qdisc classes which map 1:1 to a set of hardware

exposed queues.

By default the qdisc allocates a pfifo qdisc (packet limited first in, first

out queue) per TX queue exposed by the lower layer device. Other queuing

disciplines may be added subsequently. Packets are enqueued using the

.B map

parameter and hashed across the indicated queues in the

.B offset

and

.B count.

By default these parameters are configured by the hardware

driver to match the hardware QOS structures.

.B Channel

mode supports full offload of the mqprio options, the traffic classes, the queue

configurations and QOS attributes to the hardware. Enabled hardware can provide

hardware QOS with the ability to steer traffic flows to designated traffic

classes provided by this qdisc. Hardware based QOS is configured using the

.B shaper

parameter.

.B bw_rlimit

with minimum and maximum bandwidth rates can be used for setting

transmission rates on each traffic class. Also further qdiscs may be added

to the classes of MQPRIO to create more complex configurations.

.SH ALGORITHM

On creation with 'tc qdisc add', eight traffic classes are created mapping

priorities 0..7 to traffic classes 0..7 and priorities greater than 7 to

traffic class 0. This requires base driver support and the creation will

fail on devices that do not support hardware QOS schemes.

These defaults can be overridden using the qdisc parameters. Providing

the 'hw 0' flag allows software to run without hardware coordination.

If hardware coordination is being used and arguments are provided that

the hardware can not support then an error is returned. For many users

hardware defaults should work reasonably well.

As one specific example numerous Ethernet cards support the 802.1Q

link strict priority transmission selection algorithm (TSA). MQPRIO

enabled hardware in conjunction with the classification methods below

can provide hardware offloaded support for this TSA.

.SH CLASSIFICATION

Multiple methods are available to set the SKB priority which MQPRIO

uses to select which traffic class to enqueue the packet.

.TP

From user space

A process with sufficient privileges can encode the destination class

directly with SO_PRIORITY, see

.BR socket(7).

.TP

with iptables/nftables

An iptables/nftables rule can be created to match traffic flows and

set the priority.

.BR iptables(8)

.TP

with net_prio cgroups

The net_prio cgroup can be used to set the priority of all sockets

belong to an application. See kernel and cgroup documentation for details.

.SH QDISC PARAMETERS

.TP

num_tc

Number of traffic classes to use. Up to 16 classes supported.

.TP

map

The priority to traffic class map. Maps priorities 0..15 to a specified

traffic class.

.TP

queues

Provide count and offset of queue range for each traffic class. In the

format,

.B count@offset.

Queue ranges for each traffic classes cannot overlap and must be a

contiguous range of queues.

.TP

hw

Set to

.B 1

to support hardware offload. Set to

.B 0

to configure user specified values in software only.

.TP

mode

Set to

.B channel

for full use of the mqprio options. Use

.B dcb

to offload only TC values and use hardware QOS defaults. Supported with 'hw'

set to 1 only.

.TP

shaper

Use

.B bw_rlimit

to set bandwidth rate limits for a traffic class. Use

.B dcb

for hardware QOS defaults. Supported with 'hw' set to 1 only.

.TP

min_rate

Minimum value of bandwidth rate limit for a traffic class.

.TP

max_rate

Maximum value of bandwidth rate limit for a traffic class.

.SH AUTHORS

John Fastabend, <john.r.fastabend@intel.com>