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Linux 2.6 - man page for tc-drr (linux section 8)

TC(8)					      Linux					    TC(8)

NAME
       drr - deficit round robin scheduler

SYNOPSIS
       tc qdisc ... add drr [ quantum bytes ]

DESCRIPTION
       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  fil-
       ters  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.

ALGORITHM
       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.

PARAMETERS
       quantum
	      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.

EXAMPLE &; USAGE
       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:  clas-
       sid 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 suc-
       ceeds.  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
       done

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

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

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

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

AUTHOR
       sched_drr was written by Patrick McHardy.

iproute2				   January 2010 				    TC(8)


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