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 ] [ 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 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

       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. 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  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.

       max_rate
              Maximum value of bandwidth rate limit for a traffic class.

AUTHORS

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