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more documentation on new dummynet features.
This commit is contained in:
Luigi Rizzo
parent
03dab16e1d
commit
34ae843479
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=204758
116
sbin/ipfw/ipfw.8
116
sbin/ipfw/ipfw.8
@ -1404,7 +1404,7 @@ If not found, the match fails.
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Otherwise, the match succeeds and
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.Cm tablearg
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is set to the value extracted from the table.
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.Br
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.Pp
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This option can be useful to quickly dispatch traffic based on
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certain packet fields.
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See the
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@ -1847,7 +1847,7 @@ is also the user interface for the
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.Nm dummynet
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traffic shaper, packet scheduler and network emulator, a subsystem that
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can artificially queue, delay or drop packets
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emulator the behaviour of certain network links
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emulating the behaviour of certain network links
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or queueing systems.
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.Pp
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.Nm dummynet
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@ -1859,26 +1859,33 @@ Matching packets are then passed to either of two
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different objects, which implement the traffic regulation:
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.Bl -hang -offset XXXX
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.It Em pipe
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A pipe emulates a link with given bandwidth, propagation delay,
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A
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.Em pipe
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emulates a
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.Em link
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with given bandwidth and propagation delay,
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driven by a FIFO scheduler and a single queue with programmable
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queue size and packet loss rate.
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Packets are queued in front of the pipe as they come out from the classifier,
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and then transferred to the pipe according to the pipe's parameters.
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Packets are appended to the queue as they come out from
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.Nm ipfw ,
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and then transferred in FIFO order to the link at the desired rate.
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.It Em queue
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A queue
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A
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.Em queue
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is an abstraction used to implement packet scheduling
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using one of several packet scheduling algorithms.
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.Pp
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The queue associates a
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.Em weight
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and a reference scheduler to each flow (a flow is a set of packets
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with the same addresses and ports after masking).
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A scheduler in turn is connected to a pipe, and arbitrates
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the pipe's bandwidth among backlogged flows according to
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Packets sent to a
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.Em queue
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are first grouped into flows according to a mask on the 5-tuple.
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Flows are then passed to the scheduler associated to the
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.Em queue ,
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and each flow uses scheduling parameters (weight and others)
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as configured in the
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.Em queue
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itself.
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A scheduler in turn is connected to an emulated link,
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and arbitrates the link's bandwidth among backlogged flows according to
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weights and to the features of the scheduling algorithm in use.
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.Pp
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Note that weights are not priorities; a flow with a lower weight
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is still guaranteed to get its fraction of the bandwidth even if a
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flow with a higher weight is permanently backlogged.
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.El
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.Pp
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In practice,
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@ -1887,6 +1894,52 @@ can be used to set hard limits to the bandwidth that a flow can use, whereas
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.Em queues
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can be used to determine how different flows share the available bandwidth.
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.Pp
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A graphical representation of the binding of queues,
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flows, schedulers and links is below.
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.Bd -literal -offset indent
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(flow_mask|sched_mask) sched_mask
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+---------+ weight Wx +-------------+
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| |->-[flow]-->--| |-+
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-->--| QUEUE x | ... | | |
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| |->-[flow]-->--| SCHEDuler N | |
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+---------+ | | |
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... | +--[LINK N]-->--
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+---------+ weight Wy | | +--[LINK N]-->--
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| |->-[flow]-->--| | |
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-->--| QUEUE y | ... | | |
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| |->-[flow]-->--| | |
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+---------+ +-------------+ |
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+-------------+
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.Ed
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It is important to understand the role of the SCHED_MASK
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and FLOW_MASK, which are configured through the commands
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.Dl "ipfw sched N config mask SCHED_MASK ..."
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and
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.Dl "ipfw queue X config mask FLOW_MASK ..." .
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.Pp
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The SCHED_MASK is used to assign flows to one or more
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scheduler instances, one for each
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value of the packet's 5-fuple after applying SCHED_MASK.
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As an example, using ``src-ip 0xffffff00'' creates one instance
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for each /24 destination subnet.
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.Pp
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The FLOW_MASK, together with the SCHED_MASK, is used to split
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packets into flows. As an example, using
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``src-ip 0x000000ff''
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together with the previous SCHED_MASK makes a flow for
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each individual source address. In turn, flows for each /24
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subnet will be sent to the same scheduler instance.
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.Pp
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The above diagram holds even for the
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.Em pipe
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case, with the only restriction that a
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.Em pipe
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only supports a SCHED_MASK, and forces the use of a FIFO
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scheduler (these are for backward compatibility reasons;
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in fact, internally, a
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.Nm dummynet's
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pipe is implemented exactly as above).
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.Pp
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There are two modes of
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.Nm dummynet
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operation:
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@ -2087,9 +2140,36 @@ The following parameters can be configured for a scheduler:
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.Pp
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.Bl -tag -width indent -compact
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.It Cm type Ar {fifo | wf2qp | rr | qfq}
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specifies the scheduling algorithm to use.
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.Bl -tag -width indent -compact
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.It cm fifo
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is just a FIFO scheduler (which means that all packets
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are stored in the same queue as they arrive to the scheduler).
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FIFO has O(1) per-packet time complexity, with very low
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constants (estimate 60-80ns on a 2Ghz desktop machine)
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but gives no service guarantees.
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.It Cm wf2qp
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implements the WF2Q+ algorithm, which is a Weighted Fair Queueing
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algorithm which permits flows to share bandwidth according to
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their weights. Note that weights are not priorities; even a flow
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with a minuscule weight will never starve.
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WF2Q+ has O(log N) per-packet processing cost, where N is the number
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of flows, and is the default algorithm used by previous versions
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dummynet's queues.
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.It Cm rr
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implements the Deficit Round Robin algorithm, which has O(1) processing
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costs (roughly, 100-150ns per packet)
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and permits bandwidth allocation according to weights, but
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with poor service guarantees.
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.It Cm qfq
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implements the QFQ algorithm, which is a very fast variant of
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WF2Q+, with similar service guarantees and O(1) processing
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costs (roughly, 200-250ns per packet).
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.El
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.El
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.Pp
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plus all the parameters allowed for a pipe.
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In addition to the type, all parameters allowed for a pipe can also
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be specified for a scheduler.
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.Pp
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Finally, the following parameters can be configured for both
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pipes and queues:
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