1PIE(8) Linux PIE(8)
2
6 PIE - Proportional Integral controller-Enhanced AQM algorithm
7
9 tc qdisc ... pie [ limit PACKETS ] [ target TIME ] [ tupdate TIME ] [
10 alpha int ] [ beta int ] [ ecn | noecn ] [ bytemode | nobytemode ] [
11 dq_rate_estimator | no_dq_rate_estimator ]
12
15 Proportional Integral controller-Enhanced (PIE) is a control theoretic
16 active queue management scheme. It is based on the proportional inte‐
17 gral controller but aims to control delay. The main design goals are
18 o Low latency control
19 o High link utilization
20 o Simple implementation
21 o Guaranteed stability and fast responsiveness
22
25 PIE is designed to control delay effectively. First, an average dequeue
26 rate is estimated based on the standing queue. The rate is used to cal‐
27 culate the current delay. Then, on a periodic basis, the delay is used
28 to calculate the dropping probabilty. Finally, on arrival, a packet is
29 dropped (or marked) based on this probability.
30 PIE makes adjustments to the probability based on the trend of the
32 delay i.e. whether it is going up or down.The delay converges quickly
33 to the target value specified.
34 alpha and beta are statically chosen parameters chosen to control the
36 drop probability growth and are determined through control theoretic
37 approaches. alpha determines how the deviation between the current and
38 target latency changes probability. beta exerts additional adjustments
39 depending on the latency trend.
40 The drop probabilty is used to mark packets in ecn mode. However, as in
42 RED, beyond 10% packets are dropped based on this probability. The
43 bytemode is used to drop packets proportional to the packet size.
44 Additional details can be found in the paper cited below.
46
49 limit
50 limit on the queue size in packets. Incoming packets are dropped when
51 this limit is reached. Default is 1000 packets.
52 target
55 is the expected queue delay. The default target delay is 15ms.
56 tupdate
59 is the frequency at which the system drop probability is calculated.
60 The default is 15ms.
61 alpha
64 beta
65 alpha and beta are parameters chosen to control the drop probability.
66 These should be in the range between 0 and 32.
67 ecn | noecn
70 is used to mark packets instead of dropping. ecn to turn on ecn mode,
71 noecn to turn off ecn mode. By default, ecn is turned off.
72 bytemode | nobytemode
75 is used to scale drop probability proportional to packet size. byte‐
76 mode to turn on bytemode, nobytemode to turn off bytemode. By default,
77 bytemode is turned off.
78 dq_rate_estimator | no_dq_rate_estimator
81 is used to calculate delay using Little's law. dq_rate_estimator to
82 turn on dq_rate_estimator, no_dq_rate_estimator to turn off
83 no_dq_rate_estimator. By default, dq_rate_estimator is turned off.
84
87 # tc qdisc add dev eth0 root pie
88 # tc -s qdisc show
89 qdisc pie 8036: dev eth0 root refcnt 2 limit 1000p target 15.0ms
90 tupdate 16.0ms alpha 2 beta 20
91 Sent 31216108 bytes 20800 pkt (dropped 80, overlimits 0 requeues 0)
92 backlog 16654b 11p requeues 0
93 prob 0.006161 delay 15666us
94 pkts_in 20811 overlimit 0 dropped 80 maxq 50 ecn_mark 0
95 # tc qdisc add dev eth0 root pie dq_rate_estimator
97 # tc -s qdisc show
98 qdisc pie 8036: dev eth0 root refcnt 2 limit 1000p target 15.0ms
99 tupdate 16.0ms alpha 2 beta 20
100 Sent 63947420 bytes 42414 pkt (dropped 41, overlimits 0 requeues 0)
101 backlog 271006b 179p requeues 0
102 prob 0.000092 delay 22200us avg_dq_rate 12145996
103 pkts_in 41 overlimit 343 dropped 0 maxq 50 ecn_mark 0
104 # tc qdisc add dev eth0 root pie limit 100 target 20ms tupdate 30ms
106 ecn
107 # tc -s qdisc show
108 qdisc pie 8036: dev eth0 root refcnt 2 limit 100p target 20.0ms tup‐
109 date 32.0ms alpha 2 beta 20 ecn
110 Sent 6591724 bytes 4442 pkt (dropped 27, overlimits 0 requeues 0)
111 backlog 18168b 12p requeues 0
112 prob 0.008845 delay 11348us
113 pkts_in 4454 overlimit 0 dropped 27 maxq 65 ecn_mark 0
114 # tc qdisc add dev eth0 root pie limit 100 target 50ms tupdate 30ms
116 bytemode
117 # tc -s qdisc show
118 qdisc pie 8036: dev eth0 root refcnt 2 limit 100p target 50.0ms tup‐
119 date 32.0ms alpha 2 beta 20 bytemode
120 Sent 1616274 bytes 1137 pkt (dropped 0, overlimits 0 requeues 0)
121 backlog 13626b 9p requeues 0
122 prob 0.000000 delay 0us
123 pkts_in 1146 overlimit 0 dropped 0 maxq 23 ecn_mark 0
124
127 tc(8), tc-codel(8) tc-red(8)
128
131 o RFC 8033: https://tools.ietf.org/html/rfc8033
132
135 PIE was implemented by Vijay Subramanian and Mythili Prabhu, also the
136 authors of this man page. Please report bugs and corrections to the
137 Linux networking development mailing list at <netdev@vger.kernel.org>.
138iproute2 16 January 2014 PIE(8)