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 ] [ 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)