FQ-PIE(8)



FQ-PIE(8)                            Linux                           FQ-PIE(8)

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 pack-
       ets 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 al-
       gorithm 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-tu-
       ple of source and destination IP addresses, port numbers and IP  proto-
       col  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  cred-
       its  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 se-
       lected 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). Af-
       ter having selected a queue from which to dequeue a packet, the PIE al-
       gorithm 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 algo-
       rithm, 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 classi-
       fied. 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  calcu-
       lated.  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 pa-
       rameter requires ecn to be enabled.

   [no]ecn
       It has the same semantics as pie and can be used to  mark  packets  in-
       stead  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  byte-
       mode  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>.

iproute2                        23 January 2020                      FQ-PIE(8)

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