Signed-off-by: Vinicius Costa Gomes <vinicius.go...@intel.com> --- man/man8/tc-cbs.8 | 100 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 100 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..e84c5495 --- /dev/null +++ b/man/man8/tc-cbs.8 @@ -0,0 +1,100 @@ +.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.go...@intel.com> -- 2.14.2
