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