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 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 .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 <netdev@vger.kernel.org>.