Provided by: iproute2_6.1.0-1ubuntu6_amd64 bug

NAME

       FQ-PIE - Flow Queue Proportional Integral controller Enhanced

SYNOPSIS

       tc qdisc ... fq_pie [ limit PACKETS ] [ flows NUMBER ]
                           [ target TIME ] [ tupdate TIME ]
                           [ alpha NUMBER ] [ beta NUMBER ]
                           [ quantum BYTES ] [ memory_limit BYTES ]
                           [ ecn_prob PERENTAGE ] [ [no]ecn ]
                           [ [no]bytemode ] [ [no_]dq_rate_estimator ]

DESCRIPTION

       FQ-PIE  (Flow  Queuing  with  Proportional  Integral  controller  Enhanced)  is a queuing discipline that
       combines Flow Queuing with the PIE AQM scheme. FQ-PIE uses a Jenkins hash function to  classify  incoming
       packets  into different flows and is used to provide a fair share of the bandwidth to all the flows using
       the qdisc. Each such flow is managed by the PIE algorithm.

ALGORITHM

       The FQ-PIE algorithm consists of two logical parts: the scheduler which selects which queue to dequeue  a
       packet from, and the PIE AQM which works on each of the queues. The major work of FQ-PIE is mostly in the
       scheduling part. The interaction between the scheduler and the PIE algorithm is straight forward.

       During the enqueue stage, a hashing-based scheme is used, where flows are hashed into a number of buckets
       with  each  bucket having its own queue. The number of buckets is configurable, and presently defaults to
       1024 in the implementation.  The flow hashing is performed on the 5-tuple of source  and  destination  IP
       addresses,  port  numbers and IP protocol number. Once the packet has been successfully classified into a
       queue, it is handed over to the PIE algorithm for enqueuing. It is then added to the tail of the selected
       queue,  and  the  queue's  byte count is updated by the packet size. If the queue is not currently active
       (i.e., if it is not in either the list of new or the list of old queues) , it is added to the end of  the
       list  of  new  queues,  and  its number of credits is initiated to the configured quantum. Otherwise, the
       queue is left in its current queue list.

       During the dequeue stage, the scheduler first looks at the list of new queues; for the queue at the  head
       of  that  list,  if that queue has a negative number of credits (i.e., it has already dequeued at least a
       quantum of bytes), it is given an additional quantum of credits, the queue is put onto  the  end  of  the
       list  of  old  queues,  and the routine selects the next queue and starts again. Otherwise, that queue is
       selected for dequeue again. If the list of new queues is empty, the scheduler proceeds down the  list  of
       old  queues  in  the same fashion (checking the credits, and either selecting the queue for dequeuing, or
       adding credits and putting the queue back at the end of the list). After having  selected  a  queue  from
       which to dequeue a packet, the PIE algorithm is invoked on that queue.

       Finally,  if  the  PIE algorithm does not return a packet, then the queue must be empty and the scheduler
       does one of two things:

       If the queue selected for dequeue came from the list of new queues, it is moved to the end of the list of
       old  queues.  If  instead it came from the list of old queues, that queue is removed from the list, to be
       added back (as a new queue) the next time a packet arrives that hashes to  that  queue.  Then  (since  no
       packet was available for dequeue), the whole dequeue process is restarted from the beginning.

       If,  instead,  the  scheduler  did get a packet back from the PIE algorithm, it subtracts the size of the
       packet from the byte credits for the selected queue and returns the packet as the result of  the  dequeue
       operation.

PARAMETERS

   limit
       It is the limit on the queue size in packets. Incoming packets are dropped when the limit is reached. The
       default value is 10240 packets.

   flows
       It 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.
       The default value is 1024.

   target
       It is the queue delay which the PIE algorithm tries to maintain. The default target delay is 15ms.

   tupdate
       It is the time interval at which the system drop probability is calculated.  The default is 15ms.

   alpha
   beta
       alpha  and  beta  are  parameters  chosen  to  control the drop probability. These should be in the range
       between 0 and 32.

   quantum
       quantum signifies the number of bytes that may be dequeued from a queue  before  switching  to  the  next
       queue in the deficit round robin scheme.

   memory_limit
       It is the maximum total memory allowed for packets of all flows. The default is 32Mb.

   ecn_prob
       It  is  the drop probability threshold below which packets will be ECN marked instead of getting dropped.
       The default is 10%. Setting this parameter requires ecn to be enabled.

   [no]ecn
       It has the same semantics as pie and can be used to mark packets instead of dropping  them.  If  ecn  has
       been enabled, noecn can be used to turn it off and vice-a-versa.

   [no]bytemode
       It is used to scale drop probability proportional to packet size bytemode to turn on bytemode, nobytemode
       to turn off bytemode. By default, bytemode is turned off.

   [no_]dq_rate_estimator
       dq_rate_estimator can be used to calculate queue delay using Little's Law,  no_dq_rate_estimator  can  be
       used to calculate queue delay using timestamp. By default, dq_rate_estimator is turned off.

EXAMPLES

       # tc qdisc add dev eth0 root fq_pie
       # tc -s qdisc show dev eth0
       qdisc  fq_pie  8001:  root  refcnt 2 limit 10240p flows 1024 target 15.0ms tupdate 16.0ms alpha 2 beta 20
       quantum 1514b memory_limit 32Mb ecn_prob 10
        Sent 159173586 bytes 105261 pkt (dropped 24, overlimits 0 requeues 0)
        backlog 75700b 50p requeues 0
         pkts_in 105311 overlimit 0 overmemory 0 dropped 24 ecn_mark 0
         new_flow_count 7332 new_flows_len 0 old_flows_len 4 memory_used 108800

       # tc qdisc add dev eth0 root fq_pie dq_rate_estimator
       # tc -s qdisc show dev eth0
       qdisc fq_pie 8001: root refcnt 2 limit 10240p flows 1024 target 15.0ms tupdate 16.0ms  alpha  2  beta  20
       quantum 1514b memory_limit 32Mb ecn_prob 10 dq_rate_estimator
        Sent 8263620 bytes 5550 pkt (dropped 4, overlimits 0 requeues 0)
        backlog 805448b 532p requeues 0
         pkts_in 6082 overlimit 0 overmemory 0 dropped 4 ecn_mark 0
         new_flow_count 94 new_flows_len 0 old_flows_len 8 memory_used 1157632

SEE ALSO

       tc(8), tc-pie(8), tc-fq_codel(8)

SOURCES

       RFC 8033: https://tools.ietf.org/html/rfc8033

AUTHORS

       FQ-PIE  was  implemented by Mohit P. Tahiliani. Please report corrections to the Linux Networking mailing
       list <netdev@vger.kernel.org>.