tc-fq_codel

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  ]  [  ce_threshold
       TIME ] [ 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  sto-
       chastic  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.  De-
       fault 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  be-
       ing  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 stand-
       ing/persistent queue delay. This minimum delay is identified by  track-
       ing  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 ex-
       perienced 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 end-
       points 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 algo-
       rithms that require marking at very shallow queueing thresholds.

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)