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 ] [ ce_threshold TIME ] [ ce_threshold_selector VALUE/MASK ] [ memory_limit BYTES ]

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.

   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.

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>.

iproute2                                           4 June 2012                                       FQ_CoDel(8)