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 ]

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
       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 20ms.

   tupdate
       is the frequency at which the system drop probability is calculated.
       The default is 30ms.

   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.

EXAMPLES         top

        # tc qdisc add dev eth0 root pie
        # tc -s qdisc show
          qdisc pie 8034: dev eth0 root refcnt 2 limit 200p target 19000us
       tupdate 29000us alpha 2 beta 20
          Sent 7443524 bytes 7204 pkt (dropped 900, overlimits 0 requeues 0)
          backlog 38998b 37p requeues 0
          prob 0.123384 delay 25000us avg_dq_rate 1464840
          pkts_in 7241 overlimit 900 dropped 0 maxq 186 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 200p target 19000
       tupdate 29000 alpha 2 beta 20 ecn
          Sent 2491922 bytes 2507 pkt (dropped 214, overlimits 0 requeues 0)
          backlog 33728b 32p requeues 0
          prob 0.102262 delay 24000us avg_dq_rate 1464840
          pkts_in 2468 overlimit 214 dropped 0 maxq 192 ecn_mark 71

        # 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 200p target 19000
       tupdate 29000 alpha 2 beta 20 ecn
          Sent 2491922 bytes 2507 pkt (dropped 214, overlimits 0 requeues 0)
          backlog 33728b 32p requeues 0
          prob 0.102262 delay 24000us avg_dq_rate 1464840
          pkts_in 2468 overlimit 214 dropped 0 maxq 192 ecn_mark 71

SEE ALSO         top

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

SOURCES         top

        o IETF draft submission is at
       http://tools.ietf.org/html/draft-pan-tsvwg-pie-00
        o IEEE  Conference on High Performance Switching and Routing 2013 :
       "PIE: A Lightweight Control Scheme to Address the Bufferbloat
       Problem"

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 
       ⟨git://git.kernel.org/pub/scm/linux/kernel/git/shemminger/iproute2.git⟩
       on 2017-03-13.  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)