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+.TH FQ_CoDel 8 "4 June 2012" "iproute2" "Linux"
+.SH NAME
+CoDel \- Fair Queuing (FQ) with Controlled Delay (CoDel)
+.SH SYNOPSIS
+.B tc qdisc ... fq_codel
+[
+.B limit
+PACKETS ] [
+.B flows
+NUMBER ] [
+.B target
+TIME ] [
+.B interval
+TIME ] [
+.B quantum
+BYTES ] [
+.B ecn
+|
+.B noecn
+] [
+.B ce_threshold
+TIME ] [
+.B ce_threshold_selector
+VALUE/MASK ] [
+.B memory_limit
+BYTES ]
+
+.SH 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.
+
+.SH PARAMETERS
+.SS limit
+has the same semantics as
+.B codel
+and is the hard limit on the real queue size.
+When this limit is reached, incoming packets are dropped. Default is 10240
+packets.
+
+.SS 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
+.B limit
+parameter and the memory limit will be enforced. Default is 32 MB.
+
+
+.SS 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.
+
+.SS target
+has the same semantics as
+.B 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.
+
+.SS interval
+has the same semantics as
+.B 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 
+.BR 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.
+
+.SS 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.
+
+.SS ecn | noecn
+has the same semantics as
+.B codel
+and can be used to mark packets instead of dropping them. If
+.B ecn
+has been enabled,
+.B noecn
+can be used to turn it off and vice-a-versa. Unlike
+.B codel, ecn
+is turned on by default.
+
+.SS 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.
+
+.SS ce_threshold_selector
+sets a filter so that the
+.B 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
+.B ce_threshold
+logic be applied to the packet.
+
+.SS drop_batch
+sets the maximum number of packets to drop when
+.B limit
+or
+.B memory_limit
+is exceeded. Default value is 64.
+
+.SH EXAMPLES
+#tc qdisc add   dev eth0 root fq_codel
+.br
+#tc -s qdisc show
+.br
+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
+.br
+#tc -s qdisc show
+.br
+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
+
+
+.SH SEE ALSO
+.BR tc (8),
+.BR tc-codel (8),
+.BR tc-red (8)
+
+.SH 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>.