[iproute2 net-next 3/3] man: Add initial manpage for tc-cbs(8)

[Vinicius Costa Gomes <vinicius.gomes@intel.com>]

Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
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 man/man8/tc-cbs.8 | 100 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
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+.TH CBS 8 "18 Sept 2017" "iproute2" "Linux"
+.SH NAME
+CBS \- Credit Based Shaper (CBS) Qdisc
+.SH SYNOPSIS
+.B tc qdisc ... dev
+dev
+.B parent
+classid
+.B [ handle
+major:
+.B ] cbs idleslope
+idleslope
+.B sendslope
+sendslope
+.B hicredit
+hicredit
+.B locredit
+locredit
+
+.SH DESCRIPTION
+The CBS (Credit Based Shaper) qdisc implements the shaping algorithm
+defined by the IEEE 802.1Q-2014 Section 8.6.8.2, which applies a well
+defined rate limiting method to the traffic.
+
+This queueing discipline is intended to be used by TSN (Time Sensitive
+Networking) applications, the CBS parameters are derived directly by
+what is described by the Annex L of the IEEE 802.1Q-2014
+Sepcification. The algorithm and how it affects the latency are
+detailed there.
+
+CBS is meant to be installed under another qdisc that maps packet
+flows to traffic classes, one example is
+.BR mqprio(8).
+
+.SH PARAMETERS
+.TP
+idleslope
+Idleslope is the rate of credits that is accumulated (in kilobits per
+second) when there is at least one packet waiting for transmission.
+Packets are transmitted when the current value of credits is equal or
+greater than zero. When there is no packet to be transmitted the
+amount of credits is set to zero. This is the main tunable of the CBS
+algorithm.
+.TP
+sendslope
+Sendslope is the rate of credits that is depleted (it should be a
+negative number of kilobits per second) when a transmission is
+ocurring. It can be calculated as follows, (IEEE 802.1Q-2014 Section
+8.6.8.2 item g):
+
+sendslope = idleslope - port_transmit_rate
+
+.TP
+hicredit
+Hicredit defines the maximum amount of credits (in bytes) that can be
+accumulated. Hicredit depends on the characteristics of interfering
+traffic, 'max_interference_size' is the maximum size of any burst of
+traffic that can delay the transmission of a frame that is available
+for transmission for this traffic class, (IEEE 802.1Q-2014 Annex L,
+Equation L-3):
+
+hicredit = max_interference_size * (idleslope / port_transmit_rate)
+
+.TP
+locredit
+Locredit is the minimum amount of credits that can be reached. It is a
+function of the traffic flowing through this qdisc (IEEE 802.1Q-2014
+Annex L, Equation L-2):
+
+locredit = max_frame_size * (sendslope / port_transmit_rate)
+
+.SH EXAMPLES
+
+CBS is used to enforce a Quality of Service by limiting the data rate
+of a traffic class, to separate packets into traffic classes the user
+may choose
+.BR mqprio(8),
+and configure it like this:
+
+.EX
+# tc qdisc add dev eth0 handle 100: parent root mqprio num_tc 3 \\
+	map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 \\
+	queues 1@0 1@1 2@2 \\
+	hw 0
+.EE
+.P
+To replace the current queuing disciple by CBS in the current queueing
+discipline connected to traffic class number 0, issue:
+.P
+.EX
+# tc qdisc replace dev eth0 parent 100:4 cbs \\
+	locredit -1470 hicredit 30 sendslope -980000 idleslope 20000
+.EE
+
+These values are obtained from the following parameters, idleslope is
+20mbit/s, the transmission rate is 1Gbit/s and the maximum interfering
+frame size is 1500 bytes.
+
+.SH AUTHORS
+Vinicius Costa Gomes <vinicius.gomes@intel.com>
-- 
2.14.2