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MQPRIO(8) Linux MQPRIO(8)
NAME
MQPRIO - Multiqueue Priority Qdisc (Offloaded Hardware QOS)
SYNOPSIS
tc qdisc ... dev dev ( parent classid | root) [ handle major: ] mqprio [ num_tc tcs ] [
map P0 P1 P2... ] [ queues count1@offset1 count2@offset2 ... ] [ hw 1|0 ] [ mode
dcb|channel] ] [ shaper dcb| [ bw_rlimit min_rate min_rate1 min_rate2 ... max_rate
max_rate1 max_rate2 ... ]]
DESCRIPTION
The MQPRIO qdisc is a simple queuing discipline that allows mapping traffic flows to hard-
ware 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 map parameter and hashed across the indicated
queues in the offset and count. By default these parameters are configured by the hard-
ware driver to match the hardware QOS structures.
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 shaper parameter. bw_rlimit with mini-
mum 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.
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 al-
lows 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 rea-
sonably 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.
CLASSIFICATION
Multiple methods are available to set the SKB priority which MQPRIO uses to select which
traffic class to enqueue the packet.
From user space
A process with sufficient privileges can encode the destination class directly with
SO_PRIORITY, see socket(7).
with iptables/nftables
An iptables/nftables rule can be created to match traffic flows and set the prior-
ity. iptables(8)
with net_prio cgroups
The net_prio cgroup can be used to set the priority of all sockets belong to an ap-
plication. See kernel and cgroup documentation for details.
QDISC PARAMETERS
num_tc Number of traffic classes to use. Up to 16 classes supported.
map The priority to traffic class map. Maps priorities 0..15 to a specified traffic
class.
queues Provide count and offset of queue range for each traffic class. In the format,
count@offset. Queue ranges for each traffic classes cannot overlap and must be a
contiguous range of queues.
hw Set to 1 to support hardware offload. Set to 0 to configure user specified values
in software only.
mode Set to channel for full use of the mqprio options. Use dcb to offload only TC val-
ues and use hardware QOS defaults. Supported with 'hw' set to 1 only.
shaper Use bw_rlimit to set bandwidth rate limits for a traffic class. Use dcb for hard-
ware QOS defaults. Supported with 'hw' set to 1 only.
min_rate
Minimum value of bandwidth rate limit for a traffic class.
max_rate
Maximum value of bandwidth rate limit for a traffic class.
AUTHORS
John Fastabend, <john.r.fastabend AT intel.com>
iproute2 24 Sept 2013 MQPRIO(8)
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