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95 lines
2.7 KiB
Groff
95 lines
2.7 KiB
Groff
.TH TC 8 "January 2010" "iproute2" "Linux"
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.SH NAME
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drr \- deficit round robin scheduler
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.SH SYNOPSIS
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.B tc qdisc ... add drr
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.B [ quantum
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bytes
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.B ]
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.SH DESCRIPTION
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The Deficit Round Robin Scheduler is a classful queuing discipline as
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a more flexible replacement for Stochastic Fairness Queuing.
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Unlike SFQ, there are no built-in queues \-\- you need to add classes
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and then set up filters to classify packets accordingly.
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This can be useful e.g. for using RED qdiscs with different settings for particular
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traffic. There is no default class \-\- if a packet cannot be classified,
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it is dropped.
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.SH ALGORITHM
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Each class is assigned a deficit counter, initialized to
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.B quantum.
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DRR maintains an (internal) ''active'' list of classes whose qdiscs are
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non-empty. This list is used for dequeuing. A packet is dequeued from
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the class at the head of the list if the packet size is smaller or equal
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to the deficit counter. If the counter is too small, it is increased by
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.B quantum
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and the scheduler moves on to the next class in the active list.
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.SH PARAMETERS
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.TP
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quantum
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Amount of bytes a flow is allowed to dequeue before the scheduler moves to
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the next class. Defaults to the MTU of the interface. The minimum value is 1.
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.SH EXAMPLE & USAGE
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To attach to device eth0, using the interface MTU as its quantum:
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.P
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# tc qdisc add dev eth0 handle 1 root drr
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.P
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Adding two classes:
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.P
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# tc class add dev eth0 parent 1: classid 1:1 drr
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# tc class add dev eth0 parent 1: classid 1:2 drr
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.P
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You also need to add at least one filter to classify packets.
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.P
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# tc filter add dev eth0 protocol .. classid 1:1
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.P
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Like SFQ, DRR is only useful when it owns the queue \-\- it is a pure scheduler and does
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not delay packets. Attaching non-work-conserving qdiscs like tbf to it does not make
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sense \-\- other qdiscs in the active list will also become inactive until the dequeue
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operation succeeds. Embed DRR within another qdisc like HTB or HFSC to ensure it owns the queue.
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.P
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You can mimic SFQ behavior by assigning packets to the attached classes using the
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flow filter:
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.B tc qdisc add dev .. drr
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.B for i in .. 1024;do
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.br
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.B \ttc class add dev .. classid $handle:$(print %x $i)
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.br
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.B \ttc qdisc add dev .. fifo limit 16
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.br
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.B done
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.B tc filter add .. protocol ip .. $handle flow hash keys src,dst,proto,proto-src,proto-dst divisor 1024 perturb 10
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.SH SOURCE
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.TP
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o
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M. Shreedhar and George Varghese "Efficient Fair
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Queuing using Deficit Round Robin", Proc. SIGCOMM 95.
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.SH NOTES
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This implementation does not drop packets from the longest queue on overrun,
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as limits are handled by the individual child qdiscs.
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.SH SEE ALSO
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.BR tc (8),
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.BR tc-htb (8),
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.BR tc-sfq (8)
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.SH AUTHOR
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sched_drr was written by Patrick McHardy.
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