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1 | .TH FQ_CoDel 8 "4 June 2012" "iproute2" "Linux" |
2 | .SH NAME | |
3 | CoDel \- Fair Queuing (FQ) with Controlled Delay (CoDel) | |
4 | .SH SYNOPSIS | |
5 | .B tc qdisc ... fq_codel | |
6 | [ | |
7 | .B limit | |
8 | PACKETS ] [ | |
9 | .B flows | |
10 | NUMBER ] [ | |
11 | .B target | |
12 | TIME ] [ | |
13 | .B interval | |
14 | TIME ] [ | |
15 | .B quantum | |
16 | BYTES ] [ | |
17 | .B ecn | |
18 | | | |
19 | .B noecn | |
20 | ] | |
21 | ||
22 | .SH DESCRIPTION | |
6274b0b7 | 23 | FQ_Codel (Fair Queuing Controlled Delay) is queuing discipline that combines Fair |
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24 | Queuing with the CoDel AQM scheme. FQ_Codel uses a stochastic model to classify |
25 | incoming packets into different flows and is used to provide a fair share of the | |
26 | bandwidth to all the flows using the queue. Each such flow is managed by the | |
27 | CoDel queuing discipline. Reordering within a flow is avoided since Codel | |
28 | internally uses a FIFO queue. | |
29 | ||
30 | .SH PARAMETERS | |
31 | .SS limit | |
32 | has the same semantics as | |
33 | .B codel | |
34 | and is the hard limit on the real queue size. | |
35 | When this limit is reached, incoming packets are dropped. Default is 10240 | |
36 | packets. | |
37 | ||
38 | .SS flows | |
39 | is the number of flows into which the incoming packets are classified. Due to | |
40 | the stochastic nature of hashing, multiple flows may end up being hashed into | |
41 | the same slot. Newer flows have priority over older ones. This parameter can be | |
42 | set only at load time since memory has to be allocated for the hash table. | |
43 | Default value is 1024. | |
44 | ||
45 | .SS target | |
46 | has the same semantics as | |
47 | .B codel | |
48 | and is the acceptable minimum | |
49 | standing/persistent queue delay. This minimum delay is identified by tracking | |
a89d5329 | 50 | the local minimum queue delay that packets experience. Default value is 5ms. |
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51 | |
52 | .SS interval | |
53 | has the same semantics as | |
54 | .B codel | |
55 | and is used to ensure that the measured minimum delay does not become too stale. | |
56 | The minimum delay must be experienced in the last epoch of length .B interval. | |
57 | It should be set on the order of the worst-case RTT through the bottleneck to | |
a89d5329 | 58 | give endpoints sufficient time to react. Default value is 100ms. |
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59 | |
60 | .SS quantum | |
61 | is the number of bytes used as 'deficit' in the fair queuing algorithm. Default | |
62 | is set to 1514 bytes which corresponds to the Ethernet MTU plus the hardware | |
63 | header length of 14 bytes. | |
64 | ||
65 | .SS ecn | noecn | |
66 | has the same semantics as | |
67 | .B codel | |
a89d5329 | 68 | and can be used to mark packets instead of dropping them. If |
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69 | .B ecn |
70 | has been enabled, | |
71 | .B noecn | |
72 | can be used to turn it off and vice-a-versa. Unlike | |
73 | .B codel, ecn | |
74 | is turned on by default. | |
75 | ||
76 | .SH EXAMPLES | |
77 | #tc qdisc add dev eth0 root fq_codel | |
78 | .br | |
79 | #tc -s qdisc show | |
80 | .br | |
81 | qdisc fq_codel 8002: dev eth0 root refcnt 2 limit 10240p flows 1024 quantum 1514 | |
82 | target 5.0ms interval 100.0ms ecn | |
83 | Sent 428514 bytes 2269 pkt (dropped 0, overlimits 0 requeues 0) | |
84 | backlog 0b 0p requeues 0 | |
85 | maxpacket 256 drop_overlimit 0 new_flow_count 0 ecn_mark 0 | |
86 | new_flows_len 0 old_flows_len 0 | |
87 | ||
88 | #tc qdisc add dev eth0 root fq_codel limit 2000 target 3ms interval 40ms noecn | |
89 | .br | |
90 | #tc -s qdisc show | |
91 | .br | |
92 | qdisc fq_codel 8003: dev eth0 root refcnt 2 limit 2000p flows 1024 quantum 1514 | |
93 | target 3.0ms interval 40.0ms | |
94 | Sent 2588985006 bytes 1783629 pkt (dropped 0, overlimits 0 requeues 34869) | |
95 | backlog 0b 0p requeues 34869 | |
96 | maxpacket 65226 drop_overlimit 0 new_flow_count 73 ecn_mark 0 | |
97 | new_flows_len 1 old_flows_len 3 | |
98 | ||
99 | ||
100 | .SH SEE ALSO | |
101 | .BR tc (8), | |
102 | .BR tc-codel (8), | |
103 | .BR tc-red (8) | |
104 | ||
105 | .SH AUTHORS | |
106 | FQ_CoDel was implemented by Eric Dumazet. This manpage was written | |
107 | by Vijay Subramanian. Please report corrections to the Linux Networking | |
108 | mailing list <netdev@vger.kernel.org>. |