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Signed-Off-By: Pavel Šimerda <psimerda@redhat.com>
132 lines
4.2 KiB
Groff
132 lines
4.2 KiB
Groff
.TH PIE 8 "16 January 2014" "iproute2" "Linux"
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.SH NAME
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PIE \- Proportional Integral controller-Enhanced AQM algorithm
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.SH SYNOPSIS
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.B tc qdisc ... pie
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[
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.B limit
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PACKETS ] [
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.B target
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TIME ] [
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.B tupdate
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TIME ] [
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.B alpha
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int ] [
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.B beta
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int ] [
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.B ecn
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.B noecn
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] [
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.B bytemode
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.B nobytemode
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]
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.SH DESCRIPTION
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Proportional Integral controller-Enhanced (PIE) is a control theoretic active
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queue management scheme. It is based on the proportional integral controller but
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aims to control delay. The main design goals are
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o Low latency control
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o High link utilization
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o Simple implementation
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o Guaranteed stability and fast responsiveness
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.SH ALGORITHM
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PIE is designed to control delay effectively. First, an average dequeue rate is
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estimated based on the standing queue. The rate is used to calculate the current
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delay. Then, on a periodic basis, the delay is used to calculate the dropping
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probabilty. Finally, on arrival, a packet is dropped (or marked) based on this
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probability.
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PIE makes adjustments to the probability based on the trend of the delay i.e.
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whether it is going up or down.The delay converges quickly to the target value
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specified.
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alpha and beta are statically chosen parameters chosen to control the drop probability
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growth and are determined through control theoretic approaches. alpha determines how
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the deviation between the current and target latency changes probability. beta exerts
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additional adjustments depending on the latency trend.
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The drop probabilty is used to mark packets in ecn mode. However, as in RED,
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beyond 10% packets are dropped based on this probability. The bytemode is used
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to drop packets proportional to the packet size.
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Additional details can be found in the paper cited below.
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.SH PARAMETERS
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.SS limit
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limit on the queue size in packets. Incoming packets are dropped when this limit
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is reached. Default is 1000 packets.
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.SS target
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is the expected queue delay. The default target delay is 20ms.
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.SS tupdate
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is the frequency at which the system drop probability is calculated. The default is 30ms.
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.SS alpha
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.SS beta
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alpha and beta are parameters chosen to control the drop probability. These
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should be in the range between 0 and 32.
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.SS ecn | noecn
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is used to mark packets instead of dropping
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.B ecn
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to turn on ecn mode,
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.B noecn
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to turn off ecn mode. By default,
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.B ecn
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is turned off.
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.SS bytemode | nobytemode
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is used to scale drop probability proportional to packet size
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.B bytemode
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to turn on bytemode,
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.B nobytemode
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to turn off bytemode. By default,
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.B bytemode
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is turned off.
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.SH EXAMPLES
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# tc qdisc add dev eth0 root pie
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# tc -s qdisc show
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qdisc pie 8034: dev eth0 root refcnt 2 limit 200p target 19000us tupdate 29000us alpha 2 beta 20
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Sent 7443524 bytes 7204 pkt (dropped 900, overlimits 0 requeues 0)
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backlog 38998b 37p requeues 0
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prob 0.123384 delay 25000us avg_dq_rate 1464840
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pkts_in 7241 overlimit 900 dropped 0 maxq 186 ecn_mark 0
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# tc qdisc add dev eth0 root pie limit 100 target 20ms tupdate 30ms ecn
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# tc -s qdisc show
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qdisc pie 8036: dev eth0 root refcnt 2 limit 200p target 19000 tupdate 29000 alpha 2 beta 20 ecn
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Sent 2491922 bytes 2507 pkt (dropped 214, overlimits 0 requeues 0)
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backlog 33728b 32p requeues 0
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prob 0.102262 delay 24000us avg_dq_rate 1464840
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pkts_in 2468 overlimit 214 dropped 0 maxq 192 ecn_mark 71
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# tc qdisc add dev eth0 root pie limit 100 target 50ms tupdate 30ms bytemode
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# tc -s qdisc show
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qdisc pie 8036: dev eth0 root refcnt 2 limit 200p target 19000 tupdate 29000 alpha 2 beta 20 ecn
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Sent 2491922 bytes 2507 pkt (dropped 214, overlimits 0 requeues 0)
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backlog 33728b 32p requeues 0
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prob 0.102262 delay 24000us avg_dq_rate 1464840
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pkts_in 2468 overlimit 214 dropped 0 maxq 192 ecn_mark 71
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.SH SEE ALSO
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.BR tc (8),
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.BR tc-codel (8)
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.BR tc-red (8)
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.SH SOURCES
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o IETF draft submission is at http://tools.ietf.org/html/draft-pan-tsvwg-pie-00
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o IEEE Conference on High Performance Switching and Routing 2013 : "PIE: A
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Lightweight Control Scheme to Address the Bufferbloat Problem"
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.SH AUTHORS
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PIE was implemented by Vijay Subramanian and Mythili Prabhu, also the authors of
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this man page. Please report bugs and corrections to the Linux networking
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development mailing list at <netdev@vger.kernel.org>.
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