PIE(8)                              Linux                             PIE(8)

NAME         top

       PIE - Proportional Integral controller-Enhanced AQM algorithm

SYNOPSIS         top

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

DESCRIPTION         top

       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         top

       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.

PARAMETERS         top

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

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

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

       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.

EXAMPLES         top

        # 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
           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
        # 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
        # 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

SEE ALSO         top

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

SOURCES         top

        o RFC 8033:

AUTHORS         top

       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

COLOPHON         top

       This page is part of the iproute2 (utilities for controlling TCP/IP
       networking and traffic) project.  Information about the project can
       be found at 
       If you have a bug report for this manual page, send it to,  This page was obtained
       from the project's upstream Git repository
       ⟨⟩ on
       2019-07-28.  (At that time, the date of the most recent commit that
       was found in the repository was 2019-07-26.)  If you discover any
       rendering problems in this HTML version of the page, or you believe
       there is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

iproute2                       16 January 2014                        PIE(8)

Pages that refer to this page: tc(8)