Provided by: iproute2_4.3.0-1ubuntu3_i386 bug


       Fair Queuing (FQ) - Traffic Pacing


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


       FQ (Fair Queue) is a classless packet scheduler meant to be mostly used
       for locally generated traffic.  It is  designed  to  achieve  per  flow
       pacing.   FQ  does  flow  separation,  and  is  able  to respect pacing
       requirements set by TCP stack.  All packets belonging to a  socket  are
       considered  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_PACING_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
       window  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


       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.

       Hard limit on the maximum number of packets queued per  flow.   Default
       value is 100.

       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

       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.

       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.

       The  size  of  the  hash  table  used  for flow lookups. Each bucket is
       assigned a red-black tree for efficient  collision  sorting.   Default:

       Enable or disable flow pacing. Default is enabled.


       #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
        backlog 0b 0p requeues 54452
         1289 flows (1289 inactive, 0 throttled)
         0 gc, 31 highprio, 27411 throttled


       tc(8), socket(7)


       FQ was written by Eric Dumazet.