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       drr - deficit round robin scheduler


       tc qdisc ... add drr [ quantum bytes ]


       The Deficit Round Robin Scheduler is a classful queuing discipline as a
       more flexible replacement for Stochastic Fairness Queuing.

       Unlike SFQ, there are no built-in queues -- you need to add classes and
       then  set  up  filters  to  classify  packets accordingly.  This can be
       useful e.g. for using RED qdiscs with different settings for particular
       traffic. There is no default class -- if a packet cannot be classified,
       it is dropped.


       Each class is assigned a deficit counter, initialized to quantum.

       DRR maintains an (internal) ’’active’’ list of classes whose qdiscs are
       non-empty.  This list is used for dequeuing.  A packet is dequeued from
       the class at the head of the list if the  packet  size  is  smaller  or
       equal  to  the  deficit  counter.   If  the counter is too small, it is
       increased by quantum and the scheduler moves on to the  next  class  in
       the active list.


              Amount  of  bytes  a  flow  is  allowed  to  dequeue  before the
              scheduler moves to the next class.  Defaults to the MTU  of  the
              interface. The minimum value is 1.


       To attach to device eth0, using the interface MTU as its quantum:

       # tc qdisc add dev eth0 handle 1 root drr

       Adding two classes:

       #  tc  class  add dev eth0 parent 1: classid 1:1 drr # tc class add dev
       eth0 parent 1: classid 1:2 drr

       You also need to add at least one filter to classify packets.

       # tc filter add dev eth0 protocol .. classid 1:1

       Like SFQ, DRR is only useful when it owns the queue --  it  is  a  pure
       scheduler  and  does  not delay packets.  Attaching non-work-conserving
       qdiscs like tbf to it does not make sense -- other qdiscs in the active
       list  will  also  become inactive until the dequeue operation succeeds.
       Embed DRR within another qdisc like HTB or HFSC to ensure it  owns  the

       You can mimic SFQ behavior by assigning packets to the attached classes
       using the flow filter:

       tc qdisc add dev .. drr

       for i in .. 1024;do
            tc class add dev .. classid $handle:$(print %x $i)
            tc qdisc add dev .. fifo limit 16

       tc  filter  add  ..   protocol   ip   ..   $handle   flow   hash   keys
       src,dst,proto,proto-src,proto-dst divisor 1024 perturb 10


       o      M.  Shreedhar  and George Varghese "Efficient Fair Queuing using
              Deficit Round Robin", Proc. SIGCOMM 95.


       This implementation does not drop packets from  the  longest  queue  on
       overrun, as limits are handled by the individual child qdiscs.


       tc(8), tc-htb(8), tc-sfq(8)


       sched_drr was written by Patrick McHardy.