man/man8/tc-sfq.8 - maze/iproute2 - Git at Google

 .TH TC 8 "8 December 2001" "iproute2" "Linux"
 .SH NAME
 sfq \- Stochastic Fairness Queueing
 .SH SYNOPSIS
 .B tc qdisc ...
 .B divisor
 hashtablesize
 .B limit
 packets
 .B perturb
 seconds
 .B quantum
 bytes

 .SH DESCRIPTION

 Stochastic Fairness Queueing is a classless queueing discipline available for
 traffic control with the
 .BR tc (8)
 command.

 SFQ does not shape traffic but only schedules the transmission of packets, based on 'flows'.
 The goal is to ensure fairness so that each flow is able to send data in turn, thus preventing
 any single flow from drowning out the rest.

 This may in fact have some effect in mitigating a Denial of Service attempt.

 SFQ is work-conserving and therefore always delivers a packet if it has one available.
 .SH ALGORITHM
 On enqueueing, each packet is assigned to a hash bucket, based on the packets hash value.
 This hash value is either obtained from an external flow classifier (use
 .B
 tc filter
 to set them), or a default internal classifier if no external classifier has been configured.

 When the internal classifier is used, sfq uses
 .TP
 (i)
 Source address
 .TP
 (ii)
 Destination address
 .TP
 (iii)
 Source port
 .P
 If these are available. SFQ knows about ipv4 and ipv6 and also UDP, TCP and ESP.
 Packets with other protocols are hashed based on the 32bits representation of their
 destination and the socket they belong to. A flow corresponds mostly to a TCP/IP
 connection.

 Each of these buckets should represent a unique flow. Because multiple flows may
 get hashed to the same bucket, sfqs internal hashing algorithm may be perturbed at configurable
 intervals so that the unfairness lasts only for a short while. Perturbation may
 however cause some inadvertent packet reordering to occur.

 When dequeuing, each hashbucket with data is queried in a round robin fashion.

 The compile time maximum length of the SFQ is 128 packets, which can be spread over
 at most 128 buckets of 1024 available. In case of overflow, tail-drop is performed
 on the fullest bucket, thus maintaining fairness.

 .SH PARAMETERS
 .TP
 divisor
 Can be used to set a different hash table size, available from kernel 2.6.39 onwards.
 The specified divisor must be a power of two and cannot be larger than 65536.
 Default value: 1024.
 .TP
 limit
 Upper limit of the SFQ. Can be used to reduce the default length of 128 packets.
 .TP
 perturb
 Interval in seconds for queue algorithm perturbation. Defaults to 0, which means that
 no perturbation occurs. Do not set too low for each perturbation may cause some packet
 reordering. Advised value: 10
 This value has no effect when external flow classification is used.
 .TP
 quantum
 Amount of bytes a flow is allowed to dequeue during a round of the round robin process.
 Defaults to the MTU of the interface which is also the advised value and the minimum value.

 .SH EXAMPLE & USAGE

 To attach to device ppp0:
 .P
 # tc qdisc add dev ppp0 root sfq perturb 10
 .P
 Please note that SFQ, like all non-shaping (work-conserving) qdiscs, is only useful
 if it owns the queue.
 This is the case when the link speed equals the actually available bandwidth. This holds
 for regular phone modems, ISDN connections and direct non-switched ethernet links.
 .P
 Most often, cable modems and DSL devices do not fall into this category. The same holds
 for when connected to a switch  and trying to send data to a congested segment also
 connected to the switch.
 .P
 In this case, the effective queue does not reside within Linux and is therefore not
 available for scheduling.
 .P
 Embed SFQ in a classful qdisc to make sure it owns the queue.

 It is possible to use external classifiers with sfq, for example to hash traffic based only
 on source/destination ip addresses:
 .P
 # tc filter add ... flow hash keys src,dst perturb 30 divisor 1024
 Note that the given divisor should match the one used by sfq. If you have
 changed the sfq default of 1024, use the same value for the flow hash filter, too.


 .SH SOURCE
 .TP
 o
 Paul E. McKenney "Stochastic Fairness Queuing",
 IEEE INFOCOMM'90 Proceedings, San Francisco, 1990.

 .TP
 o
 Paul E. McKenney "Stochastic Fairness Queuing",
 "Interworking: Research and Experience", v.2, 1991, p.113-131.

 .TP
 o
 See also:
 M. Shreedhar and George Varghese "Efficient Fair
 Queuing using Deficit Round Robin", Proc. SIGCOMM 95.

 .SH SEE ALSO
 .BR tc (8)

 .SH AUTHOR
 Alexey N. Kuznetsov, <kuznet@ms2.inr.ac.ru>. This manpage maintained by
 bert hubert <ahu@ds9a.nl>
	.TH TC 8 "8 December 2001" "iproute2" "Linux"
	.SH NAME
	sfq \- Stochastic Fairness Queueing
	.SH SYNOPSIS
	.B tc qdisc ...
	.B divisor
	hashtablesize
	.B limit
	packets
	.B perturb
	seconds
	.B quantum
	bytes

	.SH DESCRIPTION

	Stochastic Fairness Queueing is a classless queueing discipline available for
	traffic control with the
	.BR tc (8)
	command.

	SFQ does not shape traffic but only schedules the transmission of packets, based on 'flows'.
	The goal is to ensure fairness so that each flow is able to send data in turn, thus preventing
	any single flow from drowning out the rest.

	This may in fact have some effect in mitigating a Denial of Service attempt.

	SFQ is work-conserving and therefore always delivers a packet if it has one available.
	.SH ALGORITHM
	On enqueueing, each packet is assigned to a hash bucket, based on the packets hash value.
	This hash value is either obtained from an external flow classifier (use
	.B
	tc filter
	to set them), or a default internal classifier if no external classifier has been configured.

	When the internal classifier is used, sfq uses
	.TP
	(i)
	Source address
	.TP
	(ii)
	Destination address
	.TP
	(iii)
	Source port
	.P
	If these are available. SFQ knows about ipv4 and ipv6 and also UDP, TCP and ESP.
	Packets with other protocols are hashed based on the 32bits representation of their
	destination and the socket they belong to. A flow corresponds mostly to a TCP/IP
	connection.

	Each of these buckets should represent a unique flow. Because multiple flows may
	get hashed to the same bucket, sfqs internal hashing algorithm may be perturbed at configurable
	intervals so that the unfairness lasts only for a short while. Perturbation may
	however cause some inadvertent packet reordering to occur.

	When dequeuing, each hashbucket with data is queried in a round robin fashion.

	The compile time maximum length of the SFQ is 128 packets, which can be spread over
	at most 128 buckets of 1024 available. In case of overflow, tail-drop is performed
	on the fullest bucket, thus maintaining fairness.

	.SH PARAMETERS
	.TP
	divisor
	Can be used to set a different hash table size, available from kernel 2.6.39 onwards.
	The specified divisor must be a power of two and cannot be larger than 65536.
	Default value: 1024.
	.TP
	limit
	Upper limit of the SFQ. Can be used to reduce the default length of 128 packets.
	.TP
	perturb
	Interval in seconds for queue algorithm perturbation. Defaults to 0, which means that
	no perturbation occurs. Do not set too low for each perturbation may cause some packet
	reordering. Advised value: 10
	This value has no effect when external flow classification is used.
	.TP
	quantum
	Amount of bytes a flow is allowed to dequeue during a round of the round robin process.
	Defaults to the MTU of the interface which is also the advised value and the minimum value.

	.SH EXAMPLE & USAGE

	To attach to device ppp0:
	.P
	# tc qdisc add dev ppp0 root sfq perturb 10
	.P
	Please note that SFQ, like all non-shaping (work-conserving) qdiscs, is only useful
	if it owns the queue.
	This is the case when the link speed equals the actually available bandwidth. This holds
	for regular phone modems, ISDN connections and direct non-switched ethernet links.
	.P
	Most often, cable modems and DSL devices do not fall into this category. The same holds
	for when connected to a switch and trying to send data to a congested segment also
	connected to the switch.
	.P
	In this case, the effective queue does not reside within Linux and is therefore not
	available for scheduling.
	.P
	Embed SFQ in a classful qdisc to make sure it owns the queue.

	It is possible to use external classifiers with sfq, for example to hash traffic based only
	on source/destination ip addresses:
	.P
	# tc filter add ... flow hash keys src,dst perturb 30 divisor 1024
	Note that the given divisor should match the one used by sfq. If you have
	changed the sfq default of 1024, use the same value for the flow hash filter, too.


	.SH SOURCE
	.TP
	o
	Paul E. McKenney "Stochastic Fairness Queuing",
	IEEE INFOCOMM'90 Proceedings, San Francisco, 1990.

	.TP
	o
	Paul E. McKenney "Stochastic Fairness Queuing",
	"Interworking: Research and Experience", v.2, 1991, p.113-131.

	.TP
	o
	See also:
	M. Shreedhar and George Varghese "Efficient Fair
	Queuing using Deficit Round Robin", Proc. SIGCOMM 95.

	.SH SEE ALSO
	.BR tc (8)

	.SH AUTHOR
	Alexey N. Kuznetsov, <kuznet@ms2.inr.ac.ru>. This manpage maintained by
	bert hubert <ahu@ds9a.nl>