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diff --git a/man/man8/tc-fq.8 b/man/man8/tc-fq.8 new file mode 100644 index 0000000..27385aa --- /dev/null +++ b/man/man8/tc-fq.8 @@ -0,0 +1,107 @@ +.TH FQ 8 "10 Sept 2015" "iproute2" "Linux" +.SH NAME +FQ \- Fair Queue traffic policing +.SH SYNOPSIS +.B tc qdisc ... fq +[ +.B limit +PACKETS ] [ +.B flow_limit +PACKETS ] [ +.B quantum +BYTES ] [ +.B initial_quantum +BYTES ] [ +.B maxrate +RATE ] [ +.B buckets +NUMBER ] [ +.B orphan_mask +NUMBER ] [ +.B pacing +| +.B nopacing +] [ +.B ce_threshold +TIME ] + +.SH DESCRIPTION +FQ (Fair Queue) is a classless packet scheduler meant to be mostly +used for locally generated traffic. It is designed to achieve per flow pacing. +FQ does flow separation, and is able to respect pacing requirements set by TCP stack. +All packets belonging to a socket are considered as a 'flow'. +For non local packets (router workload), packet hash is used as fallback. + +An application can specify a maximum pacing rate using the +.B SO_MAX_PACING_RATE +setsockopt call. This packet scheduler adds delay between packets to +respect rate limitation set on each socket. Note that after linux-4.20, linux adopted EDT (Earliest Departure Time) +and TCP directly sets the appropriate Departure Time for each skb. + +Dequeueing happens in a round-robin fashion. +A special FIFO queue is reserved for high priority packets ( +.B TC_PRIO_CONTROL +priority), such packets are always dequeued first. + +FQ is non-work-conserving. + +TCP pacing is good for flows having idle times, as the congestion +window permits TCP stack to queue a possibly large number of packets. +This removes the 'slow start after idle' choice, badly hitting +large BDP flows and applications delivering chunks of data such as video streams. + +.SH PARAMETERS +.SS limit +Hard limit on the real queue size. When this limit is reached, new packets +are dropped. If the value is lowered, packets are dropped so that the new limit is +met. Default is 10000 packets. +.SS flow_limit +Hard limit on the maximum number of packets queued per flow. +Default value is 100. +.SS quantum +The credit per dequeue RR round, i.e. the amount of bytes a flow is allowed to +dequeue at once. A larger value means a longer time period before the next flow +will be served. +Default is 2 * interface MTU bytes. +.SS initial_quantum +The initial sending rate credit, i.e. the amount of bytes a new flow is allowed +to dequeue initially. +This is specifically meant to allow using IW10 without added delay. +Default is 10 * interface MTU, i.e. 15140 for 'standard' ethernet. +.SS maxrate +Maximum sending rate of a flow. Default is unlimited. +Application specific setting via +.B SO_MAX_PACING_RATE +is ignored only if it is larger than this value. +.SS buckets +The size of the hash table used for flow lookups. Each bucket is assigned a +red-black tree for efficient collision sorting. +Default: 1024. +.SS orphan_mask +For packets not owned by a socket, fq is able to mask a part of skb->hash +and reduce number of buckets associated with the traffic. This is a DDOS +prevention mechanism, and the default is 1023 (meaning no more than 1024 flows +are allocated for these packets) +.SS [no]pacing +Enable or disable flow pacing. Default is enabled. +.SS ce_threshold +sets a threshold above which all packets are marked with ECN Congestion +Experienced. This is useful for DCTCP-style congestion control algorithms that +require marking at very shallow queueing thresholds. + +.SH EXAMPLES +#tc qdisc add dev eth0 root fq ce_threshold 4ms +.br +#tc -s -d qdisc show dev eth0 +.br +qdisc fq 8001: dev eth0 root refcnt 2 limit 10000p flow_limit 100p buckets 1024 orphan_mask 1023 quantum 3028b initial_quantum 15140b low_rate_threshold 550Kbit refill_delay 40.0ms ce_threshold 4.0ms + Sent 72149092 bytes 48062 pkt (dropped 2176, overlimits 0 requeues 0) + backlog 1937920b 1280p requeues 0 + flows 34 (inactive 17 throttled 0) + gc 0 highprio 0 throttled 0 ce_mark 47622 flows_plimit 2176 +.br +.SH SEE ALSO +.BR tc (8), +.BR socket (7) +.SH AUTHORS +FQ was written by Eric Dumazet. |