tc qdisc ... dev dev ( parent classid | root) [ handle major: ] mqprio
[ numtc tcs ] [ map P0 P1 P2... ] [ queues count1@offset1 count2@off-
set2 ... ] [ hw 1|0 ]
The MQPRIO qdisc is a simple queuing discipline that allows mapping
traffic flows to hardware queue ranges using priorities and a config-
urable priority to traffic class mapping. A traffic class in this con-
text 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
hardware driver to match the hardware QOS structures.
Enabled hardware can provide hardware QOS with the ability to steer
traffic flows to designated traffic classes provided by this qdisc.
Configuring the hardware based QOS mechanism is outside the scope of
this qdisc. Tools such as lldpad and ethtool exist to provide this
functionality. Also further qdiscs may be added to the classes of
MQPRIO to create more complex configurations.
On creation with 'tc qdisc add', eight traffic classes are created map-
ping 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 pro-
vide hardware offloaded support for this TSA.
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).
An iptables/nftables rule can be created to match traffic flows
and set the priority. iptables(8)
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 use hardware QOS defaults. Set to 0 to override
hardware defaults with user specified values.
John Fastabend, <email@example.com>
iproute2 24 Sept 2013 MQPRIO(8)
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