Provided by: iproute2_6.1.0-1ubuntu6_amd64 bug

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>.