CoDel - Fair Queuing (FQ) with Controlled Delay (CoDel)
tc qdisc ... fq_codel [ limit PACKETS ] [ flows NUMBER ] [ target TIME
] [ interval TIME ] [ quantum BYTES ] [ ecn | noecn ]
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
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.
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.
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.
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.
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.
#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
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
#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
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
tc(8), tc-codel(8), tc-red(8)
FQ_CoDel was implemented by Eric Dumazet. This manpage was written by
Vijay Subramanian. Please report corrections to the Linux Networking
mailing list <email@example.com>.