| .TH PIE 8 "16 January 2014" "iproute2" "Linux" |
| .SH NAME |
| PIE \- Proportional Integral controller-Enhanced AQM algorithm |
| .SH SYNOPSIS |
| .B tc qdisc ... pie |
| [ |
| .B limit |
| PACKETS ] [ |
| .B target |
| TIME ] [ |
| .B tupdate |
| TIME ] [ |
| .B alpha |
| int ] [ |
| .B beta |
| int ] [ |
| .B ecn |
| | |
| .B noecn |
| ] [ |
| .B bytemode |
| | |
| .B nobytemode |
| ] |
| |
| .SH DESCRIPTION |
| Proportional Integral controller-Enhanced (PIE) is a control theoretic active |
| queue management scheme. It is based on the proportional integral controller but |
| aims to control delay. The main design goals are |
| o Low latency control |
| o High link utilization |
| o Simple implementation |
| o Guaranteed stability and fast responsiveness |
| |
| .SH ALGORITHM |
| PIE is designed to control delay effectively. First, an average dequeue rate is |
| estimated based on the standing queue. The rate is used to calculate the current |
| delay. Then, on a periodic basis, the delay is used to calculate the dropping |
| probabilty. Finally, on arrival, a packet is dropped (or marked) based on this |
| probability. |
| |
| PIE makes adjustments to the probability based on the trend of the delay i.e. |
| whether it is going up or down.The delay converges quickly to the target value |
| specified. |
| |
| alpha and beta are statically chosen parameters chosen to control the drop probability |
| growth and are determined through control theoretic approaches. alpha determines how |
| the deviation between the current and target latency changes probability. beta exerts |
| additional adjustments depending on the latency trend. |
| |
| The drop probabilty is used to mark packets in ecn mode. However, as in RED, |
| beyond 10% packets are dropped based on this probability. The bytemode is used |
| to drop packets proportional to the packet size. |
| |
| Additional details can be found in the paper cited below. |
| |
| .SH PARAMETERS |
| .SS limit |
| limit on the queue size in packets. Incoming packets are dropped when this limit |
| is reached. Default is 1000 packets. |
| |
| .SS target |
| is the expected queue delay. The default target delay is 15ms. |
| |
| .SS tupdate |
| is the frequency at which the system drop probability is calculated. The default is 15ms. |
| |
| .SS alpha |
| .SS beta |
| alpha and beta are parameters chosen to control the drop probability. These |
| should be in the range between 0 and 32. |
| |
| .SS ecn | noecn |
| is used to mark packets instead of dropping |
| .B ecn |
| to turn on ecn mode, |
| .B noecn |
| to turn off ecn mode. By default, |
| .B ecn |
| is turned off. |
| |
| .SS bytemode | nobytemode |
| is used to scale drop probability proportional to packet size |
| .B bytemode |
| to turn on bytemode, |
| .B nobytemode |
| to turn off bytemode. By default, |
| .B bytemode |
| is turned off. |
| |
| .SH EXAMPLES |
| # tc qdisc add dev eth0 root pie |
| # tc -s qdisc show |
| qdisc pie 8036: dev eth0 root refcnt 2 limit 1000p target 15.0ms tupdate 16.0ms alpha 2 beta 20 |
| Sent 31216108 bytes 20800 pkt (dropped 80, overlimits 0 requeues 0) |
| backlog 16654b 11p requeues 0 |
| prob 0.006161 delay 15666us avg_dq_rate 1159667 |
| pkts_in 20811 overlimit 0 dropped 80 maxq 50 ecn_mark 0 |
| |
| # tc qdisc add dev eth0 root pie limit 100 target 20ms tupdate 30ms ecn |
| # tc -s qdisc show |
| qdisc pie 8036: dev eth0 root refcnt 2 limit 100p target 20.0ms tupdate 32.0ms alpha 2 beta 20 ecn |
| Sent 6591724 bytes 4442 pkt (dropped 27, overlimits 0 requeues 0) |
| backlog 18168b 12p requeues 0 |
| prob 0.008845 delay 11348us avg_dq_rate 1342773 |
| pkts_in 4454 overlimit 0 dropped 27 maxq 65 ecn_mark 0 |
| |
| # tc qdisc add dev eth0 root pie limit 100 target 50ms tupdate 30ms bytemode |
| # tc -s qdisc show |
| qdisc pie 8036: dev eth0 root refcnt 2 limit 100p target 50.0ms tupdate 32.0ms alpha 2 beta 20 bytemode |
| Sent 1616274 bytes 1137 pkt (dropped 0, overlimits 0 requeues 0) |
| backlog 13626b 9p requeues 0 |
| prob 0.000000 delay 0us avg_dq_rate 0 |
| pkts_in 1146 overlimit 0 dropped 0 maxq 23 ecn_mark 0 |
| |
| .SH SEE ALSO |
| .BR tc (8), |
| .BR tc-codel (8) |
| .BR tc-red (8) |
| |
| .SH SOURCES |
| o RFC 8033: https://tools.ietf.org/html/rfc8033 |
| |
| .SH AUTHORS |
| PIE was implemented by Vijay Subramanian and Mythili Prabhu, also the authors of |
| this man page. Please report bugs and corrections to the Linux networking |
| development mailing list at <netdev@vger.kernel.org>. |