алгоритм AQM с улучшенным пропорциональным интегральным контроллером (Proportional Integral controller-Enhanced AQM algorithm)
Имя (Name)
PIE - Proportional Integral controller-Enhanced AQM algorithm
Синопсис (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 ]
Описание (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
Алгоритм (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.
Параметры (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.
Примеры (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
Смотри также (See also)
tc(8), tc-codel(8) tc-red(8)
Источники (Sources)
o RFC 8033: https://tools.ietf.org/html/rfc8033
