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 Controled  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>.