| .TH FQ-PIE 8 "23 January 2020" "iproute2" "Linux" |
| |
| .SH NAME |
| |
| FQ-PIE - Flow Queue Proportional Integral controller Enhanced |
| |
| .SH SYNOPSIS |
| |
| .B tc qdisc ... fq_pie |
| [ \fBlimit\fR PACKETS ] [ \fBflows\fR NUMBER ] |
| .br |
| \ |
| [ \fBtarget\fR TIME ] [ \fBtupdate\fR TIME ] |
| .br |
| \ |
| [ \fBalpha\fR NUMBER ] [ \fBbeta\fR NUMBER ] |
| .br |
| \ |
| [ \fBquantum\fR BYTES ] [ \fBmemory_limit\fR BYTES ] |
| .br |
| \ |
| [ \fBecn_prob\fR PERENTAGE ] [ [\fBno\fR]\fBecn\fR ] |
| .br |
| \ |
| [ [\fBno\fR]\fBbytemode\fR ] [ [\fBno_\fR]\fBdq_rate_estimator\fR ] |
| |
| .SH 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. |
| |
| .SH 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. |
| |
| .SH PARAMETERS |
| .SS 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. |
| |
| .SS 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. |
| |
| .SS target |
| It is the queue delay which the PIE algorithm tries to maintain. The default |
| target delay is 15ms. |
| |
| .SS tupdate |
| It is the time interval at which the system drop probability is calculated. |
| The default is 15ms. |
| |
| .SS alpha |
| .SS beta |
| alpha and beta are parameters chosen to control the drop probability. These |
| should be in the range between 0 and 32. |
| |
| .SS 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. |
| |
| .SS memory_limit |
| It is the maximum total memory allowed for packets of all flows. The default is |
| 32Mb. |
| |
| .SS 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 |
| \fBecn\fR to be enabled. |
| |
| .SS \fR[\fBno\fR]\fBecn\fR |
| It has the same semantics as \fBpie\fR and can be used to mark packets |
| instead of dropping them. If \fBecn\fR has been enabled, \fBnoecn\fR can |
| be used to turn it off and vice-a-versa. |
| |
| .SS \fR[\fBno\fR]\fBbytemode\fR |
| It is used to scale drop probability proportional to packet size |
| \fBbytemode\fR to turn on bytemode, \fBnobytemode\fR to turn off |
| bytemode. By default, \fBbytemode\fR is turned off. |
| |
| .SS \fR[\fBno_\fR]\fBdq_rate_estimator\fR |
| \fBdq_rate_estimator\fR can be used to calculate queue delay using Little's |
| Law, \fBno_dq_rate_estimator\fR can be used to calculate queue delay |
| using timestamp. By default, \fBdq_rate_estimator\fR is turned off. |
| |
| .SH EXAMPLES |
| # tc qdisc add dev eth0 root fq_pie |
| .br |
| # tc -s qdisc show dev eth0 |
| .br |
| 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 |
| .br |
| # tc -s qdisc show dev eth0 |
| .br |
| 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 |
| |
| .SH SEE ALSO |
| .BR tc (8), |
| .BR tc-pie (8), |
| .BR tc-fq_codel (8) |
| |
| .SH SOURCES |
| RFC 8033: https://tools.ietf.org/html/rfc8033 |
| |
| .SH AUTHORS |
| FQ-PIE was implemented by Mohit P. Tahiliani. Please report corrections to the |
| Linux Networking mailing list <netdev@vger.kernel.org>. |