tc-pie(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | ALGORITHM | PARAMETERS | EXAMPLES | SEE ALSO | SOURCES | AUTHORS | COLOPHON

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 ] [ dq_rate_estimator | no_dq_rate_estimator ]

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 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         top

   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         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 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         top

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

SOURCES         top

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

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
       <netdev@vger.kernel.org>.

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 
       ⟨http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2⟩.
       If you have a bug report for this manual page, send it to
       netdev@vger.kernel.org, shemminger@osdl.org.  This page was
       obtained from the project's upstream Git repository
       ⟨https://git.kernel.org/pub/scm/network/iproute2/iproute2.git⟩ on
       2021-08-27.  (At that time, the date of the most recent commit
       that was found in the repository was 2021-08-18.)  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 man-pages@man7.org

iproute2                     16 January 2014                      PIE(8)

Pages that refer to this page: tc(8)tc-fq_pie(8)