tc-fq_codel(8) — Linux manual page


FQ_CoDel(8)                       Linux                      FQ_CoDel(8)

NAME         top

       CoDel - Fair Queuing (FQ) with Controlled Delay (CoDel)

SYNOPSIS         top

       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 ]

DESCRIPTION         top

       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.

PARAMETERS         top

       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.

       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.

       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.

       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.

       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.

       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.

       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

       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.

       sets the maximum number of packets to drop when limit or
       memory_limit is exceeded. Default value is 64.

EXAMPLES         top

       #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
          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

SEE ALSO         top

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

AUTHORS         top

       FQ_CoDel was implemented by Eric Dumazet. This manpage was
       written by Vijay Subramanian. Please report corrections to the
       Linux Networking mailing list <>.

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 
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       obtained from the project's upstream Git repository
       ⟨⟩ on
       2023-12-22.  (At that time, the date of the most recent commit
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iproute2                       4 June 2012                   FQ_CoDel(8)

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