tc-mqprio(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | ALGORITHM | CLASSIFICATION | QDISC PARAMETERS | SEE ALSO | EXAMPLE | AUTHORS | COLOPHON

MQPRIO(8)                         Linux                        MQPRIO(8)

NAME         top

       MQPRIO - Multiqueue Priority Qdisc (Offloaded Hardware QOS)

SYNOPSIS         top

       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 ... ]
               [ fp FP0 FP1 FP2 ... ]

DESCRIPTION         top

       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.

       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 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.

ALGORITHM         top

       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         top

       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         top

       num_tc Number of traffic classes to use. Up to 16 classes
              supported.  You cannot have more classes than queues

       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.  The
              default value of this parameter is 1

       mode   Set to channel for full use of the mqprio options. Use dcb
              to offload only TC values 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 hardware QOS defaults. Supported with
              'hw' set to 1 only.

       min_rate
              Minimum value of bandwidth rate limit for a traffic class.
              Supported only when the 'shaper' argument is set to
              'bw_rlimit'.

       max_rate
              Maximum value of bandwidth rate limit for a traffic class.
              Supported only when the 'shaper' argument is set to
              'bw_rlimit'.

       fp     Selects whether traffic classes are express (deliver
              packets via the eMAC) or preemptible (deliver packets via
              the pMAC), according to IEEE 802.1Q-2018 clause 6.7.2
              Frame preemption. Takes the form of an array (one element
              per traffic class) with values being 'E' (for express) or
              'P' (for preemptible).

              Multiple priorities which map to the same traffic class,
              as well as multiple TXQs which map to the same traffic
              class, must have the same FP attributes.  To interpret the
              FP as an attribute per priority, the 'map' argument can be
              used for translation. To interpret FP as an attribute per
              TXQ, the 'queues' argument can be used for translation.

              Traffic classes are express by default. The argument is
              supported only with 'hw' set to 1. Preemptible traffic
              classes are accepted only if the device has a MAC Merge
              layer configurable through ethtool(8).

SEE ALSO         top

       ethtool(8)

EXAMPLE         top

       The following example shows how to attach priorities to 4 traffic
       classes ("num_tc 4"), and then how to pair these traffic classes
       with 4 hardware queues with mqprio, with hardware coordination
       ("hw 1", or does not specified, because 1 is the default value).
       Traffic class 0 (tc0) is mapped to hardware queue 0 (q0), tc1 is
       mapped to q1, tc2 is mapped to q2, and tc3 is mapped q3.

       # tc qdisc add dev eth0 root mqprio               num_tc 4               map 0 0 0 0 1 1 1 1 2 2 2 2 3 3 3 3               queues 1@0 1@1 1@2 1@3               hw 1

       The next example shows how to attach priorities to 3 traffic
       classes ("num_tc 3"), and how to pair these traffic classes with
       4 queues, without hardware coordination ("hw 0").  Traffic class
       0 (tc0) is mapped to hardware queue 0 (q0), tc1 is mapped to q1,
       tc2 and is mapped to q2 and q3, where the queue selection between
       these two queues is somewhat randomly decided.

       # tc qdisc add dev eth0 root mqprio               num_tc 3               map 0 0 0 0 1 1 1 1 2 2 2 2 2 2 2 2               queues 1@0 1@1 2@2               hw 0

       In both cases from above the priority values from 0 to 3
       (prio0-3) are mapped to tc0, prio4-7 are mapped to tc1, and the
       prio8-11 are mapped to tc2 ("map" attribute). The last four
       priority values (prio12-15) are mapped in different ways in the
       two examples.  They are mapped to tc3 in the first example and
       mapped to tc2 in the second example.  The values of these two
       examples are the following:

        ┌────┬────┬───────┐  ┌────┬────┬────────┐
        │Prio│ tc │ queue │  │Prio│ tc │  queue │
        ├────┼────┼───────┤  ├────┼────┼────────┤
        │  0 │  0 │     0 │  │  0 │  0 │      0 │
        │  1 │  0 │     0 │  │  1 │  0 │      0 │
        │  2 │  0 │     0 │  │  2 │  0 │      0 │
        │  3 │  0 │     0 │  │  3 │  0 │      0 │
        │  4 │  1 │     1 │  │  4 │  1 │      1 │
        │  5 │  1 │     1 │  │  5 │  1 │      1 │
        │  6 │  1 │     1 │  │  6 │  1 │      1 │
        │  7 │  1 │     1 │  │  7 │  1 │      1 │
        │  8 │  2 │     2 │  │  8 │  2 │ 2 or 3 │
        │  9 │  2 │     2 │  │  9 │  2 │ 2 or 3 │
        │ 10 │  2 │     2 │  │ 10 │  2 │ 2 or 3 │
        │ 11 │  2 │     2 │  │ 11 │  2 │ 2 or 3 │
        │ 12 │  3 │     3 │  │ 12 │  2 │ 2 or 3 │
        │ 13 │  3 │     3 │  │ 13 │  2 │ 2 or 3 │
        │ 14 │  3 │     3 │  │ 14 │  2 │ 2 or 3 │
        │ 15 │  3 │     3 │  │ 15 │  2 │ 2 or 3 │
        └────┴────┴───────┘  └────┴────┴────────┘
              example1             example2

       Another example of queue mapping is the following.  There are 5
       traffic classes, and there are 8 hardware queues.

       # tc qdisc add dev eth0 root mqprio               num_tc 5               map 0 0 0 1 1 1 1 2 2 3 3 4 4 4 4 4               queues 1@0 2@1 1@3 1@4 3@5

       The value mapping is the following for this example:

               ┌───────┐
        tc0────┤Queue 0│◄────1@0
               ├───────┤
             ┌─┤Queue 1│◄────2@1
        tc1──┤ ├───────┤
             └─┤Queue 2│
               ├───────┤
        tc2────┤Queue 3│◄────1@3
               ├───────┤
        tc3────┤Queue 4│◄────1@4
               ├───────┤
             ┌─┤Queue 5│◄────3@5
             │ ├───────┤
        tc4──┼─┤Queue 6│
             │ ├───────┤
             └─┤Queue 7│
               └───────┘

AUTHORS         top

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

COLOPHON         top

       This page is part of the iproute2 (utilities for controlling
       TCP/IP networking and traffic) project.  Information about the
       project can be found at 
       ⟨http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2⟩.
       If you have a bug report for this manual page, send it to
       netdev@vger.kernel.org, shemminger@osdl.org.  This page was
       obtained from the project's upstream Git repository
       ⟨https://git.kernel.org/pub/scm/network/iproute2/iproute2.git⟩ on
       2023-12-22.  (At that time, the date of the most recent commit
       that was found in the repository was 2023-12-20.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to man-pages@man7.org

iproute2                      24 Sept 2013                     MQPRIO(8)

Pages that refer to this page: tc(8)tc-taprio(8)