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NAME
MQPRIO - Multiqueue Priority Qdisc (Offloaded Hardware QOS)
SYNOPSIS
tc qdisc ... dev dev ( parent classid | root) [ handle major: ] mqprio [ numtc tcs ] [ map P0 P1 P2... ]
[ queues count1@offset1 count2@offset2 ... ] [ hw 1|0 ]
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 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.
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.
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 priority. iptables(8)
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.
QDISC PARAMETERS
num_tc Number of traffic classes to use upto 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 use hardware QOS defaults. Set to 0 to override hardware defaults with user specified
values.
AUTHORS
John Fastabend, <john.r.fastabend@intel.com>