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NAME | SYNOPSIS | DESCRIPTION | ALGORITHM | PARAMETERS | EXAMPLES | SEE ALSO | SOURCES | AUTHORS | COLOPHON |
FQ-PIE(8) Linux FQ-PIE(8)
FQ-PIE - Flow Queue Proportional Integral controller Enhanced
tc qdisc ... fq_pie [ limit PACKETS ] [ flows NUMBER ]
[ target TIME ] [ tupdate TIME ]
[ alpha NUMBER ] [ beta NUMBER ]
[ quantum BYTES ] [ memory_limit BYTES ]
[ ecn_prob PERENTAGE ] [ [no]ecn ]
[ [no]bytemode ] [ [no_]dq_rate_estimator ]
FQ-PIE (Flow Queuing with Proportional Integral controller Enhanced)
is a queuing discipline that combines Flow Queuing with the PIE AQM
scheme. FQ-PIE uses a Jenkins hash function to classify incoming
packets into different flows and is used to provide a fair share of
the bandwidth to all the flows using the qdisc. Each such flow is
managed by the PIE algorithm.
The FQ-PIE algorithm consists of two logical parts: the scheduler
which selects which queue to dequeue a packet from, and the PIE AQM
which works on each of the queues. The major work of FQ-PIE is mostly
in the scheduling part. The interaction between the scheduler and the
PIE algorithm is straight forward.
During the enqueue stage, a hashing-based scheme is used, where flows
are hashed into a number of buckets with each bucket having its own
queue. The number of buckets is configurable, and presently defaults
to 1024 in the implementation. The flow hashing is performed on the
5-tuple of source and destination IP addresses, port numbers and IP
protocol number. Once the packet has been successfully classified
into a queue, it is handed over to the PIE algorithm for enqueuing.
It is then added to the tail of the selected queue, and the queue's
byte count is updated by the packet size. If the queue is not
currently active (i.e., if it is not in either the list of new or the
list of old queues) , it is added to the end of the list of new
queues, and its number of credits is initiated to the configured
quantum. Otherwise, the queue is left in its current queue list.
During the dequeue stage, the scheduler first looks at the list of
new queues; for the queue at the head of that list, if that queue has
a negative number of credits (i.e., it has already dequeued at least
a quantum of bytes), it is given an additional quantum of credits,
the queue is put onto the end of the list of old queues, and the
routine selects the next queue and starts again. Otherwise, that
queue is selected for dequeue again. If the list of new queues is
empty, the scheduler proceeds down the list of old queues in the same
fashion (checking the credits, and either selecting the queue for
dequeuing, or adding credits and putting the queue back at the end of
the list). After having selected a queue from which to dequeue a
packet, the PIE algorithm is invoked on that queue.
Finally, if the PIE algorithm does not return a packet, then the
queue must be empty and the scheduler does one of two things:
If the queue selected for dequeue came from the list of new queues,
it is moved to the end of the list of old queues. If instead it came
from the list of old queues, that queue is removed from the list, to
be added back (as a new queue) the next time a packet arrives that
hashes to that queue. Then (since no packet was available for
dequeue), the whole dequeue process is restarted from the beginning.
If, instead, the scheduler did get a packet back from the PIE
algorithm, it subtracts the size of the packet from the byte credits
for the selected queue and returns the packet as the result of the
dequeue operation.
limit
It is the limit on the queue size in packets. Incoming packets are
dropped when the limit is reached. The default value is 10240
packets.
flows
It is the number of flows into which the incoming packets are
classified. Due to the stochastic nature of hashing, multiple flows
may end up being hashed into the same slot. Newer flows have priority
over older ones. This parameter can be set only at load time since
memory has to be allocated for the hash table. The default value is
1024.
target
It is the queue delay which the PIE algorithm tries to maintain. The
default target delay is 15ms.
tupdate
It is the time interval 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.
quantum
quantum signifies the number of bytes that may be dequeued from a
queue before switching to the next queue in the deficit round robin
scheme.
memory_limit
It is the maximum total memory allowed for packets of all flows. The
default is 32Mb.
ecn_prob
It is the drop probability threshold below which packets will be ECN
marked instead of getting dropped. The default is 10%. Setting this
parameter requires ecn to be enabled.
[no]ecn
It has the same semantics as pie and can be used to mark packets
instead of dropping them. If ecn has been enabled, noecn can be used
to turn it off and vice-a-versa.
[no]bytemode
It 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.
[no_]dq_rate_estimator
dq_rate_estimator can be used to calculate queue delay using Little's
Law, no_dq_rate_estimator can be used to calculate queue delay using
timestamp. By default, dq_rate_estimator is turned off.
# tc qdisc add dev eth0 root fq_pie
# tc -s qdisc show dev eth0
qdisc fq_pie 8001: root refcnt 2 limit 10240p flows 1024 target
15.0ms tupdate 16.0ms alpha 2 beta 20 quantum 1514b memory_limit 32Mb
ecn_prob 10
Sent 159173586 bytes 105261 pkt (dropped 24, overlimits 0 requeues
0)
backlog 75700b 50p requeues 0
pkts_in 105311 overlimit 0 overmemory 0 dropped 24 ecn_mark 0
new_flow_count 7332 new_flows_len 0 old_flows_len 4 memory_used
108800
# tc qdisc add dev eth0 root fq_pie dq_rate_estimator
# tc -s qdisc show dev eth0
qdisc fq_pie 8001: root refcnt 2 limit 10240p flows 1024 target
15.0ms tupdate 16.0ms alpha 2 beta 20 quantum 1514b memory_limit 32Mb
ecn_prob 10 dq_rate_estimator
Sent 8263620 bytes 5550 pkt (dropped 4, overlimits 0 requeues 0)
backlog 805448b 532p requeues 0
pkts_in 6082 overlimit 0 overmemory 0 dropped 4 ecn_mark 0
new_flow_count 94 new_flows_len 0 old_flows_len 8 memory_used
1157632
tc(8), tc-pie(8), tc-fq_codel(8)
RFC 8033: https://tools.ietf.org/html/rfc8033
FQ-PIE was implemented by Mohit P. Tahiliani. Please report
corrections to the Linux Networking mailing list
<netdev@vger.kernel.org>.
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
2020-08-13. (At that time, the date of the most recent commit that
was found in the repository was 2020-06-24.) 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 23 January 2020 FQ-PIE(8)