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

       FQ-PIE - Flow Queue Proportional Integral controller Enhanced

       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 ]

       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.

       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

       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 ad‐
       ditional 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  dequeu‐
       ing,  or  adding credits and putting the queue back at the end of the list). After having selected a queue from which to de‐
       queue 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

       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 in‐
       stead 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.

       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.

       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.

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

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

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

       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.

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

       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.

       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.

       It  is used to scale drop probability proportional to packet size bytemode to turn on bytemode, nobytemode to turn off byte‐
       mode. By default, bytemode is turned off.

       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.

       # 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 mem‐
       ory_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  mem‐
       ory_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

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

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

       FQ-PIE  was  implemented  by  Mohit  P.  Tahiliani.  Please  report  corrections  to the Linux Networking mailing list <net‐

iproute2                                                  23 January 2020                                                 FQ-PIE(8)