TC(8)                                                          Linux                                                          TC(8)

       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

       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 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

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

       sched_drr was written by Patrick McHardy.

iproute2                                                    January 2010                                                      TC(8)