NAME

       PIE - Proportional Integral controller-Enhanced AQM algorithm

SYNOPSIS

       tc  qdisc  ... pie [ limit PACKETS ] [ target TIME ] [ tupdate TIME ] [ alpha int ] [ beta
       int ] [ ecn | noecn ] [ bytemode | nobytemode ] [ dq_rate_estimator | no_dq_rate_estimator
       ]

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

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 probability. 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 probability 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.

PARAMETERS

   limit
       limit on the queue size in packets. Incoming  packets  are  dropped  when  this  limit  is
       reached. Default is 1000 packets.

   target
       is the expected queue delay. The default target delay is 15ms.

   tupdate
       is the frequency at which the system drop probability is calculated. The default is 15ms.

   alpha
   beta
       alpha  and  beta are parameters chosen to control the drop probability. These should be in
       the range between 0 and 32.

   ecn | noecn
       is used to mark packets instead of dropping.  ecn to turn on ecn mode, noecn to  turn  off
       ecn mode. By default, ecn is turned off.

   bytemode | nobytemode
       is  used  to  scale  drop  probability  proportional  to packet size.  bytemode to turn on
       bytemode, nobytemode to turn off bytemode. By default, bytemode is turned off.

   dq_rate_estimator | no_dq_rate_estimator
       is  used  to  calculate  delay  using  Little's  law.   dq_rate_estimator   to   turn   on
       dq_rate_estimator,  no_dq_rate_estimator  to  turn  off  no_dq_rate_estimator. By default,
       dq_rate_estimator is turned off.

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
            pkts_in 20811 overlimit 0 dropped 80 maxq 50 ecn_mark 0

        # tc qdisc add dev eth0 root pie dq_rate_estimator
        # 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 63947420 bytes 42414 pkt (dropped 41, overlimits 0 requeues 0)
           backlog 271006b 179p requeues 0
            prob 0.000092 delay 22200us avg_dq_rate 12145996
            pkts_in 41 overlimit 343 dropped 0 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
            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
            pkts_in 1146 overlimit 0 dropped 0 maxq 23 ecn_mark 0

SEE ALSO

       tc(8), tc-codel(8) tc-red(8)

SOURCES

        o RFC 8033: https://tools.ietf.org/html/rfc8033

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>.