1FQ(8)                                Linux                               FQ(8)
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NAME

6       FQ - Fair Queue traffic policing
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SYNOPSIS

9       tc  qdisc  ...  fq  [  limit PACKETS ] [ flow_limit PACKETS ] [ quantum
10       BYTES ] [ initial_quantum BYTES ] [ maxrate RATE ] [ buckets  NUMBER  ]
11       [ pacing | nopacing ]
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DESCRIPTION

15       FQ (Fair Queue) is a classless packet scheduler meant to be mostly used
16       for locally generated traffic.  It is designed to achieve per flow pac‐
17       ing.   FQ  does flow separation, and is able to respect pacing require‐
18       ments set by TCP stack.  All packets belonging to a socket are  consid‐
19       ered  as  a  'flow'.   For  non local packets (router workload), packet
20       rxhash is used as fallback.
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22       An application can specify a maximum pacing rate using the  SO_MAX_PAC‐
23       ING_RATE  setsockopt  call.   This  packet scheduler adds delay between
24       packets to respect rate limitation set by TCP stack.
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26       Dequeueing happens in a round-robin fashion.  A special FIFO  queue  is
27       reserved  for  high  priority packets ( TC_PRIO_CONTROL priority), such
28       packets are always dequeued first.
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30       FQ is non-work-conserving.
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32       TCP pacing is good for flows having idle times, as the congestion  win‐
33       dow  permits  TCP  stack  to  queue a possibly large number of packets.
34       This removes the 'slow start after idle' choice,  badly  hitting  large
35       BDP  flows  and  applications  delivering  chunks of data such as video
36       streams.
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PARAMETERS

40   limit
41       Hard limit on the real queue size. When  this  limit  is  reached,  new
42       packets  are  dropped.  If the value is lowered, packets are dropped so
43       that the new limit is met. Default is 10000 packets.
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45   flow_limit
46       Hard limit on the maximum number of packets queued per  flow.   Default
47       value is 100.
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49   quantum
50       The  credit  per  dequeue  RR round, i.e. the amount of bytes a flow is
51       allowed to dequeue at once. A larger value means a longer  time  period
52       before  the  next  flow  will  be served.  Default is 2 * interface MTU
53       bytes.
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55   initial_quantum
56       The initial sending rate credit, i.e. the amount of bytes a new flow is
57       allowed  to  dequeue  initially.   This  is specifically meant to allow
58       using IW10 without added delay.  Default is 10 *  interface  MTU,  i.e.
59       15140 for 'standard' ethernet.
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61   maxrate
62       Maximum  sending  rate  of  a flow.  Default is unlimited.  Application
63       specific setting via SO_MAX_PACING_RATE is ignored only if it is larger
64       than this value.
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66   buckets
67       The  size  of  the  hash  table  used  for flow lookups. Each bucket is
68       assigned a red-black tree for efficient  collision  sorting.   Default:
69       1024.
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71   [no]pacing
72       Enable or disable flow pacing. Default is enabled.
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EXAMPLES

75       #tc qdisc add dev eth0 root fq
76       #tc -s -d qdisc
77       qdisc  fq  8003:  dev  eth0  root refcnt 2 limit 10000p flow_limit 100p
78       buckets 1024 quantum 3028 initial_quantum 15140
79        Sent 503727981 bytes 1146972 pkt (dropped  0,  overlimits  0  requeues
80       54452)
81        backlog 0b 0p requeues 54452
82         1289 flows (1289 inactive, 0 throttled)
83         0 gc, 31 highprio, 27411 throttled
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SEE ALSO

86       tc(8), socket(7)
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AUTHORS

89       FQ was written by Eric Dumazet.
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93iproute2                         10 Sept 2015                            FQ(8)
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