MQPRIO - Multiqueue Priority Qdisc (Offloaded Hardware QOS)


   tc  qdisc ... dev dev ( parent classid | root) [ handle major: ] mqprio
   [  numtc  tcs  ]  [  map  P0  P1  P2...   ]  [  queues   count1@offset1
   count2@offset2 ...  ] [ hw 1|0 ]


   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.


   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 details.


   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.


   John Fastabend, <>


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