[iproute2,net-next,v2,3/3] man: Add initial manpage for tc-cbs(8)

Message ID 20171011004652.15630-3-vinicius.gomes@intel.com
State Under Review
Delegated to: Jeff Kirsher
Headers show
  • [iproute2,net-next,v2,1/3] update headers with CBS API [ONLY FOR TESTING]
Related show

Commit Message

Vinicius Costa Gomes Oct. 11, 2017, 12:46 a.m.
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
 man/man8/tc-cbs.8 | 112 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 112 insertions(+)
 create mode 100644 man/man8/tc-cbs.8


diff --git a/man/man8/tc-cbs.8 b/man/man8/tc-cbs.8
new file mode 100644
index 00000000..97e00c84
--- /dev/null
+++ b/man/man8/tc-cbs.8
@@ -0,0 +1,112 @@ 
+.TH CBS 8 "18 Sept 2017" "iproute2" "Linux"
+CBS \- Credit Based Shaper (CBS) Qdisc
+.B tc qdisc ... dev
+.B parent
+.B [ handle
+.B ] cbs idleslope
+.B sendslope
+.B hicredit
+.B locredit
+.B [ offload
+.B ]
+The CBS (Credit Based Shaper) qdisc implements the shaping algorithm
+defined by the IEEE 802.1Q-2014 Section, 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).
+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
+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
+ item g):
+sendslope = idleslope - port_transmit_rate
+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)
+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)
+.B offload
+is 1,
+.BR cbs(8)
+will try to configure the network interface so the CBS algorithm runs
+in the controller. The default is 0.
+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:
+# 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
+To replace the current queuing disciple by CBS in the current queueing
+discipline connected to traffic class number 0, issue:
+# tc qdisc replace dev eth0 parent 100:4 cbs \\
+	locredit -1470 hicredit 30 sendslope -980000 idleslope 20000
+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.
+Vinicius Costa Gomes <vinicius.gomes@intel.com>