man: Add initial manpage for tc-etf(8)

Add an initial manpage for tc-etf covering all config options, basic
concepts and operation modes.

Signed-off-by: Jesus Sanchez-Palencia <jesus.sanchez-palencia@intel.com>
Signed-off-by: David Ahern <dsahern@gmail.com>

diff --git a/man/man8/tc-etf.8 b/man/man8/tc-etf.8
new file mode 100644 (file)
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+.TH ETF 8 "05 Jul 2018" "iproute2" "Linux"
+.SH NAME
+ETF \- Earliest TxTime First (ETF) Qdisc
+.SH SYNOPSIS
+.B tc qdisc ... dev
+dev
+.B parent
+classid
+.B [ handle
+major:
+.B ] etf clockid
+clockid
+.B [ delta
+delta_nsecs
+.B ] [ deadline_mode ]
+.B [ offload ]
+
+.SH DESCRIPTION
+The ETF (Earliest TxTime First) qdisc allows applications to control
+the instant when a packet should be dequeued from the traffic control
+layer into the netdevice. If
+.B offload
+is configured and supported by the network interface card, the it will
+also control when packets leave the network controller.
+
+ETF achieves that by buffering packets until a configurable time
+before their transmission time (i.e. txtime, or deadline), which can
+be configured through the
+.B delta
+option.
+
+The qdisc uses a rb-tree internally so packets are always 'ordered' by
+their txtime and will be dequeued following the (next) earliest txtime
+first.
+
+It relies on the SO_TXTIME socket option and the SCM_TXTIME CMSG in
+each packet field to configure the behavior of time dependent sockets:
+the clockid to be used as a reference, if the expected mode of txtime
+for that socket is deadline or strict mode, and if packet drops should
+be reported on the socket's error queue. See
+.BR socket(7)
+for more information.
+
+The etf qdisc will drop any packets with a txtime in the past, or if a
+packet expires while waiting for being dequeued.
+
+This queueing discipline is intended to be used by TSN (Time Sensitive
+Networking) applications, and it exposes a traffic shaping functionality
+that is commonly documented as "Launch Time" or "Time-Based Scheduling"
+by vendors and the documentation of network interface controllers.
+
+ETF is meant to be installed under another qdisc that maps packet flows
+to traffic classes, one example is
+.BR mqprio(8).
+
+.SH PARAMETERS
+.TP
+clockid
+.br
+Specifies the clock to be used by qdisc's internal timer for measuring
+time and scheduling events. The qdisc expects that packets passing
+through it to be using this same
+.B clockid
+as the reference of their txtime timestamps. It will drop packets
+coming from sockets that do not comply with that.
+
+For more information about time and clocks on Linux, please refer
+to
+.BR time(7)
+and
+.BR clock_gettime(3).
+
+.TP
+delta
+.br
+After enqueueing or dequeueing a packet, the qdisc will schedule its
+next wake-up time for the next txtime minus this delta value.
+This means
+.B delta
+can be used as a fudge factor for the scheduler latency of a system.
+This value must be specified in nanoseconds.
+The default value is 0 nanoseconds.
+
+.TP
+deadline_mode
+.br
+When
+.B deadline_mode
+is set, the qdisc will handle txtime with a different semantics,
+changed from a 'strict' transmission time to a deadline.
+In practice, this means during the dequeue flow
+.BR etf(8)
+will set the txtime of the packet being dequeued to 'now'.
+The default is for this option to be disabled.
+
+.TP
+offload
+.br
+When
+.B offload
+is set,
+.BR etf(8)
+will try to configure the network interface so time-based transmission
+arbitration is enabled in the controller. This feature is commonly
+referred to as "Launch Time" or "Time-Based Scheduling" by the
+documentation of network interface controllers.
+The default is for this option to be disabled.
+
+.SH EXAMPLES
+
+ETF is used to enforce a Quality of Service. It controls when each
+packets should be dequeued and transmitted, and can be used for
+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 queueing discipline by ETF in traffic class
+number 0, issue:
+.P
+.EX
+# tc qdisc replace dev eth0 parent 100:1 etf \\
+       clockid CLOCK_TAI delta 300000 offload
+.EE
+
+With the options above, etf will be configured to use CLOCK_TAI as
+its clockid_t, will schedule packets for 300 us before their txtime,
+and will enable the functionality on that in the network interface
+card. Deadline mode will not be configured for this mode.
+
+.SH AUTHORS
+Jesus Sanchez-Palencia <jesus.sanchez-palencia@intel.com>
+.br
+Vinicius Costa Gomes <vinicius.gomes@intel.com>