Provided by: iproute_20111117-1ubuntu2_amd64 bug


       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 queue.

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

       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.