Manual: tc-fq_pie

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 Queu‐
       ing  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 in‐
       teraction 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 implementa‐
       tion.  The flow hashing is performed on the 5-tuple of source and destination IP addresses, port numbers and IP	pro‐
       tocol  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 calcu‐
       late 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 .

iproute2					       23 January 2020						   FQ-PIE(8)