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>