man/man8/tc-pie.8

   1 .TH PIE 8 "16 January 2014" "iproute2" "Linux"
   2 .SH NAME
   3 PIE \- Proportional Integral controller-Enhanced AQM algorithm
   4 .SH SYNOPSIS
   5 .B tc qdisc ... pie
   6 [
   7 .B limit
   8 PACKETS ] [
   9 .B target
  10 TIME ] [
  11 .B tupdate
  12 TIME ] [
  13 .B alpha
  14 int ] [
  15 .B beta
  16 int ] [
  17 .B ecn
  18 |
  19 .B noecn
  20 ] [
  21 .B bytemode
  22 |
  23 .B nobytemode
  24 ]
  25
  26 .SH DESCRIPTION
  27 Proportional Integral controller-Enhanced (PIE) is a control theoretic active
  28 queue management scheme. It is based on the proportional integral controller but
  29 aims to control delay. The main design goals are
  30  o Low latency control
  31  o High link utilization
  32  o Simple implementation
  33  o Guaranteed stability and fast responsiveness
  34
  35 .SH ALGORITHM
  36 PIE is designed to control delay effectively. First, an average dequeue rate is
  37 estimated based on the standing queue. The rate is used to calculate the current
  38 delay. Then, on a periodic basis, the delay is used to calculate the dropping
  39 probabilty. Finally, on arrival, a packet is dropped (or marked) based on this
  40 probability.
  41
  42 PIE makes adjustments to the probability based on the trend of the delay i.e.
  43 whether it is going up or down.The delay converges quickly to the target value
  44 specified.
  45
  46 alpha and beta are statically chosen parameters chosen to control the drop probability
  47 growth and are determined through control theoretic approaches. alpha determines how
  48 the deviation between the current and target latency changes probability. beta exerts
  49 additional adjustments depending on the latency trend.
  50
  51 The drop probabilty is used to mark packets in ecn mode. However, as in RED,
  52 beyond 10% packets are dropped based on this probability. The bytemode is used
  53 to drop packets proportional to the packet size.
  54
  55 Additional details can be found in the paper cited below.
  56
  57 .SH PARAMETERS
  58 .SS limit
  59 limit on the queue size in packets. Incoming packets are dropped when this limit
  60 is reached. Default is 1000 packets.
  61
  62 .SS target
  63 is the expected queue delay. The default target delay is 15ms.
  64
  65 .SS tupdate
  66 is the frequency at which the system drop probability is calculated. The default is 15ms.
  67
  68 .SS alpha
  69 .SS beta
  70 alpha and beta are parameters chosen to control the drop probability. These
  71 should be in the range between 0 and 32.
  72
  73 .SS ecn | noecn
  74 is used to mark packets instead of dropping
  75 .B ecn
  76 to turn on ecn mode,
  77 .B noecn
  78 to turn off ecn mode. By default,
  79 .B ecn
  80 is turned off.
  81
  82 .SS bytemode | nobytemode
  83 is used to scale drop probability proportional to packet size
  84 .B bytemode
  85 to turn on bytemode,
  86 .B nobytemode
  87 to turn off bytemode. By default,
  88 .B bytemode
  89 is turned off.
  90
  91 .SH EXAMPLES
  92  # tc qdisc add dev eth0 root pie
  93  # tc -s qdisc show
  94    qdisc pie 8036: dev eth0 root refcnt 2 limit 1000p target 15.0ms tupdate 16.0ms alpha 2 beta 20
  95     Sent 31216108 bytes 20800 pkt (dropped 80, overlimits 0 requeues 0)
  96     backlog 16654b 11p requeues 0
  97    prob 0.006161 delay 15666us avg_dq_rate 1159667
  98    pkts_in 20811 overlimit 0 dropped 80 maxq 50 ecn_mark 0
  99
 100  # tc qdisc add dev eth0 root pie limit 100 target 20ms tupdate 30ms ecn
 101  # tc -s qdisc show
 102    qdisc pie 8036: dev eth0 root refcnt 2 limit 100p target 20.0ms tupdate 32.0ms alpha 2 beta 20 ecn
 103     Sent 6591724 bytes 4442 pkt (dropped 27, overlimits 0 requeues 0)
 104     backlog 18168b 12p requeues 0
 105    prob 0.008845 delay 11348us avg_dq_rate 1342773
 106    pkts_in 4454 overlimit 0 dropped 27 maxq 65 ecn_mark 0
 107
 108  # tc qdisc add dev eth0 root pie limit 100 target 50ms tupdate 30ms bytemode
 109  # tc -s qdisc show
 110    qdisc pie 8036: dev eth0 root refcnt 2 limit 100p target 50.0ms tupdate 32.0ms alpha 2 beta 20 bytemode
 111     Sent 1616274 bytes 1137 pkt (dropped 0, overlimits 0 requeues 0)
 112     backlog 13626b 9p requeues 0
 113    prob 0.000000 delay 0us avg_dq_rate 0
 114    pkts_in 1146 overlimit 0 dropped 0 maxq 23 ecn_mark 0
 115
 116 .SH SEE ALSO
 117 .BR tc (8),
 118 .BR tc-codel (8)
 119 .BR tc-red (8)
 120
 121 .SH SOURCES
 122  o RFC 8033: https://tools.ietf.org/html/rfc8033
 123
 124 .SH AUTHORS
 125 PIE was implemented by Vijay Subramanian and Mythili Prabhu, also the authors of
 126 this man page. Please report bugs and corrections to the Linux networking
 127 development mailing list at <netdev@vger.kernel.org>.