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FQ(8)                                Linux                               FQ(8)

NAME
       FQ - Fair Queue traffic policing
SYNOPSIS
       tc  qdisc  ...  fq  [  limit PACKETS ] [ flow_limit PACKETS ] [ quantum
       BYTES ] [ initial_quantum BYTES ] [ maxrate RATE ] [ buckets  NUMBER  ]
       [ pacing | nopacing ]

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

PARAMETERS
   limit
       Hard limit on the real queue size. When  this  limit  is  reached,  new
       packets  are  dropped.  If the value is lowered, packets are dropped so
       that the new limit is met. Default is 10000 packets.
   flow_limit
       Hard limit on the maximum number of packets queued per  flow.   Default
       value is 100.
   quantum
       The  credit  per  dequeue  RR round, i.e. the amount of bytes a flow is
       allowed to dequeue at once. A larger value means a longer  time  period
       before  the  next  flow  will  be served.  Default is 2 * interface MTU
       bytes.
   initial_quantum
       The initial sending rate credit, i.e. the amount of bytes a new flow is
       allowed  to  dequeue  initially.   This  is specifically meant to allow
       using IW10 without added delay.  Default is 10 *  interface  MTU,  i.e.
       15140 for 'standard' ethernet.
   maxrate
       Maximum  sending  rate  of  a flow.  Default is unlimited.  Application
       specific setting via SO_MAX_PACING_RATE is ignored only if it is larger
       than this value.
   buckets
       The  size  of  the  hash  table  used  for flow lookups. Each bucket is
       assigned a red-black tree for efficient  collision  sorting.   Default:
       1024.
   [no]pacing
       Enable or disable flow pacing. Default is enabled.
EXAMPLES
       #tc qdisc add dev eth0 root fq
       #tc -s -d qdisc
       qdisc  fq  8003:  dev  eth0  root refcnt 2 limit 10000p flow_limit 100p
       buckets 1024 quantum 3028 initial_quantum 15140
        Sent 503727981 bytes 1146972 pkt (dropped  0,  overlimits  0  requeues
       54452)
        backlog 0b 0p requeues 54452
         1289 flows (1289 inactive, 0 throttled)
         0 gc, 31 highprio, 27411 throttled
SEE ALSO
       tc(8), socket(7)
AUTHORS
       FQ was written by Eric Dumazet.

iproute2                         10 Sept 2015                            FQ(8)