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93 lines
2.9 KiB
93 lines
2.9 KiB
4 months ago
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.TH FQ 8 "10 Sept 2015" "iproute2" "Linux"
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.SH NAME
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FQ \- Fair Queue traffic policing
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.SH SYNOPSIS
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.B tc qdisc ... fq
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[
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.B limit
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PACKETS ] [
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.B flow_limit
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PACKETS ] [
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.B quantum
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BYTES ] [
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.B initial_quantum
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BYTES ] [
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.B maxrate
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RATE ] [
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.B buckets
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NUMBER ] [
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.B pacing
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.B nopacing
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]
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.SH DESCRIPTION
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FQ (Fair Queue) is a classless packet scheduler meant to be mostly
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used for locally generated traffic. It is designed to achieve per flow pacing.
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FQ does flow separation, and is able to respect pacing requirements set by TCP stack.
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All packets belonging to a socket are considered as a 'flow'.
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For non local packets (router workload), packet rxhash is used as fallback.
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An application can specify a maximum pacing rate using the
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.B SO_MAX_PACING_RATE
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setsockopt call. This packet scheduler adds delay between packets to
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respect rate limitation set by TCP stack.
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Dequeueing happens in a round-robin fashion.
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A special FIFO queue is reserved for high priority packets (
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.B TC_PRIO_CONTROL
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priority), such packets are always dequeued first.
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FQ is non-work-conserving.
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TCP pacing is good for flows having idle times, as the congestion
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window permits TCP stack to queue a possibly large number of packets.
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This removes the 'slow start after idle' choice, badly hitting
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large BDP flows and applications delivering chunks of data such as video streams.
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.SH PARAMETERS
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.SS limit
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Hard limit on the real queue size. When this limit is reached, new packets
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are dropped. If the value is lowered, packets are dropped so that the new limit is
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met. Default is 10000 packets.
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.SS flow_limit
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Hard limit on the maximum number of packets queued per flow.
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Default value is 100.
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.SS quantum
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The credit per dequeue RR round, i.e. the amount of bytes a flow is allowed to
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dequeue at once. A larger value means a longer time period before the next flow
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will be served.
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Default is 2 * interface MTU bytes.
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.SS initial_quantum
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The initial sending rate credit, i.e. the amount of bytes a new flow is allowed
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to dequeue initially.
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This is specifically meant to allow using IW10 without added delay.
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Default is 10 * interface MTU, i.e. 15140 for 'standard' ethernet.
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.SS maxrate
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Maximum sending rate of a flow. Default is unlimited.
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Application specific setting via
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.B SO_MAX_PACING_RATE
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is ignored only if it is larger than this value.
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.SS buckets
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The size of the hash table used for flow lookups. Each bucket is assigned a
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red-black tree for efficient collision sorting.
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Default: 1024.
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.SS [no]pacing
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Enable or disable flow pacing. Default is enabled.
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.SH EXAMPLES
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#tc qdisc add dev eth0 root fq
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.br
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#tc -s -d qdisc
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.br
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qdisc fq 8003: dev eth0 root refcnt 2 limit 10000p flow_limit 100p buckets 1024 quantum 3028 initial_quantum 15140
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Sent 503727981 bytes 1146972 pkt (dropped 0, overlimits 0 requeues 54452)
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backlog 0b 0p requeues 54452
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1289 flows (1289 inactive, 0 throttled)
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0 gc, 31 highprio, 27411 throttled
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.br
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.SH SEE ALSO
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.BR tc (8),
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.BR socket (7)
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.SH AUTHORS
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FQ was written by Eric Dumazet.
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