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FQ_CoDel(8)                                   Linux                                   FQ_CoDel(8)

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

SYNOPSIS
       tc qdisc ... fq_codel [ limit PACKETS ] [ flows NUMBER ] [ target TIME ] [ interval TIME ]
       [ quantum BYTES ] [ ecn | noecn ]

DESCRIPTION
       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
   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.

   flows
       is the number of flows into which the incoming packets are classified. Due to the stochasā€
       tic 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
       .B 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.

EXAMPLES
       #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

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

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

iproute2                                   4 June 2012                                FQ_CoDel(8)

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