tc-fq_pie(8) - man - phpMan

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  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 num‐
       ber 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 al‐
       ready 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 stochas‐
       tic 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 get‐
       ting 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 byte‐
       mode, 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_estima‐‐
       tor  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 Network‐
       ing mailing list <netdev AT vger.org>.



iproute2                                   23 January 2020                                 FQ-PIE(8)