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NAME | SYNOPSIS | DESCRIPTION | PARAMETERS | EXAMPLES | SEE ALSO | AUTHORS | COLOPHON |
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FQ_CoDel(8) Linux FQ_CoDel(8)
CoDel - Fair Queuing (FQ) with Controlled Delay (CoDel)
tc qdisc ... fq_codel [ limit PACKETS ] [ flows NUMBER ] [ target
TIME ] [ interval TIME ] [ quantum BYTES ] [ ecn | noecn ] [
ce_threshold TIME ] [ ce_threshold_selector VALUE/MASK ] [
memory_limit BYTES ]
FQ_Codel (Fair Queuing Controlled Delay) is queuing discipline
that combines Fair Queuing with the CoDel AQM scheme. FQ_Codel
uses a stochastic model to classify incoming packets into
different flows and is used to provide a fair share of the
bandwidth to all the flows using the queue. Each such flow is
managed by the CoDel queuing discipline. Reordering within a flow
is avoided since Codel internally uses a FIFO queue.
limit
has the same semantics as codel and is the hard limit on the real
queue size. When this limit is reached, incoming packets are
dropped. Default is 10240 packets.
memory_limit
sets a limit on the total number of bytes that can be queued in
this FQ-CoDel instance. The lower of the packet limit of the limit
parameter and the memory limit will be enforced. Default is 32 MB.
flows
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. Default
value is 1024.
target
has the same semantics as codel and is the acceptable minimum
standing/persistent queue delay. This minimum delay is identified
by tracking the local minimum queue delay that packets experience.
Default value is 5ms.
interval
has the same semantics as codel and is used to ensure that the
measured minimum delay does not become too stale. The minimum
delay must be experienced in the last epoch of length interval.
It should be set on the order of the worst-case RTT through the
bottleneck to give endpoints sufficient time to react. Default
value is 100ms.
quantum
is the number of bytes used as 'deficit' in the fair queuing
algorithm. Default is set to 1514 bytes which corresponds to the
Ethernet MTU plus the hardware header length of 14 bytes.
ecn | noecn
has the same semantics as codel 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. Unlike codel, ecn is turned
on by default.
ce_threshold
sets a threshold above which all packets are marked with ECN
Congestion Experienced. This is useful for DCTCP-style congestion
control algorithms that require marking at very shallow queueing
thresholds.
ce_threshold_selector
sets a filter so that the ce_threshold feature is applied to only
a subset of the traffic seen by the qdisc. If set, the MASK value
will be applied as a bitwise AND to the diffserv/ECN byte of the
IP header, and only if the result of this masking equals VALUE,
will the ce_threshold logic be applied to the packet.
drop_batch
sets the maximum number of packets to drop when limit or
memory_limit is exceeded. Default value is 64.
#tc qdisc add dev eth0 root fq_codel
#tc -s qdisc show
qdisc fq_codel 8002: dev eth0 root refcnt 2 limit 10240p flows
1024 quantum 1514
target 5.0ms interval 100.0ms ecn
Sent 428514 bytes 2269 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
maxpacket 256 drop_overlimit 0 new_flow_count 0 ecn_mark 0
new_flows_len 0 old_flows_len 0
#tc qdisc add dev eth0 root fq_codel limit 2000 target 3ms
interval 40ms noecn
#tc -s qdisc show
qdisc fq_codel 8003: dev eth0 root refcnt 2 limit 2000p flows 1024
quantum 1514 target 3.0ms interval 40.0ms
Sent 2588985006 bytes 1783629 pkt (dropped 0, overlimits 0
requeues 34869)
backlog 0b 0p requeues 34869
maxpacket 65226 drop_overlimit 0 new_flow_count 73 ecn_mark 0
new_flows_len 1 old_flows_len 3
tc(8), tc-codel(8), tc-red(8)
FQ_CoDel was implemented by Eric Dumazet. This manpage was written
by Vijay Subramanian. Please report corrections to the Linux
Networking mailing list <[email protected]>.
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
[email protected], [email protected]. This page was
obtained from the project's upstream Git repository
⟨https://git.kernel.org/pub/scm/network/iproute2/iproute2.git⟩ on
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-08-08.) 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 [email protected]
iproute2 4 June 2012 FQ_CoDel(8)
Pages that refer to this page: ovs-vswitchd.conf.db(5), tc(8), tc-cake(8), tc-fq_pie(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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