MQPRIO - Multiqueue Priority Qdisc (Offloaded Hardware QOS)
tc qdisc ... dev
dev ( parent
classid | root) [ handle
major: ] mqprio [ numtc
tcs ] [ map
P0 P1 P2... ] [
count1@offset1 count2@offset2 ... ] [ hw
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
parameter and hashed across the indicated queues in the
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
exist to provide this functionality. Also
further qdiscs may be added to the classes of MQPRIO to create more complex
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.
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
- Number of traffic classes to use. Up to 16 classes
- The priority to traffic class map. Maps priorities 0..15 to
a specified traffic class.
- 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.
- Set to 1 to use hardware QOS defaults. Set to
0 to override hardware defaults with user specified values.
John Fastabend, <firstname.lastname@example.org>