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>
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Jesus Sanchez-Palencia
David Ahern
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.TH ETF 8 "05 Jul 2018" "iproute2" "Linux"
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.SH NAME
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ETF \- Earliest TxTime First (ETF) Qdisc
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.SH SYNOPSIS
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.B tc qdisc ... dev
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dev
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.B parent
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classid
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.B [ handle
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major:
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.B ] etf clockid
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clockid
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.B [ delta
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delta_nsecs
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.B ] [ deadline_mode ]
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.B [ offload ]
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.SH DESCRIPTION
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The ETF (Earliest TxTime First) qdisc allows applications to control
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the instant when a packet should be dequeued from the traffic control
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layer into the netdevice. If
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.B offload
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is configured and supported by the network interface card, the it will
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also control when packets leave the network controller.
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ETF achieves that by buffering packets until a configurable time
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before their transmission time (i.e. txtime, or deadline), which can
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be configured through the
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.B delta
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option.
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The qdisc uses a rb-tree internally so packets are always 'ordered' by
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their txtime and will be dequeued following the (next) earliest txtime
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first.
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It relies on the SO_TXTIME socket option and the SCM_TXTIME CMSG in
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each packet field to configure the behavior of time dependent sockets:
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the clockid to be used as a reference, if the expected mode of txtime
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for that socket is deadline or strict mode, and if packet drops should
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be reported on the socket's error queue. See
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.BR socket(7)
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for more information.
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The etf qdisc will drop any packets with a txtime in the past, or if a
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packet expires while waiting for being dequeued.
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This queueing discipline is intended to be used by TSN (Time Sensitive
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Networking) applications, and it exposes a traffic shaping functionality
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that is commonly documented as "Launch Time" or "Time-Based Scheduling"
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by vendors and the documentation of network interface controllers.
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ETF is meant to be installed under another qdisc that maps packet flows
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to traffic classes, one example is
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.BR mqprio(8).
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.SH PARAMETERS
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.TP
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clockid
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.br
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Specifies the clock to be used by qdisc's internal timer for measuring
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time and scheduling events. The qdisc expects that packets passing
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through it to be using this same
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.B clockid
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as the reference of their txtime timestamps. It will drop packets
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coming from sockets that do not comply with that.
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For more information about time and clocks on Linux, please refer
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to
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.BR time(7)
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and
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.BR clock_gettime(3).
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.TP
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delta
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.br
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After enqueueing or dequeueing a packet, the qdisc will schedule its
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next wake-up time for the next txtime minus this delta value.
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This means
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.B delta
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can be used as a fudge factor for the scheduler latency of a system.
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This value must be specified in nanoseconds.
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The default value is 0 nanoseconds.
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.TP
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deadline_mode
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.br
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When
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.B deadline_mode
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is set, the qdisc will handle txtime with a different semantics,
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changed from a 'strict' transmission time to a deadline.
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In practice, this means during the dequeue flow
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.BR etf(8)
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will set the txtime of the packet being dequeued to 'now'.
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The default is for this option to be disabled.
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.TP
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offload
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.br
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When
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.B offload
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is set,
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.BR etf(8)
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will try to configure the network interface so time-based transmission
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arbitration is enabled in the controller. This feature is commonly
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referred to as "Launch Time" or "Time-Based Scheduling" by the
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documentation of network interface controllers.
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The default is for this option to be disabled.
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.SH EXAMPLES
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ETF is used to enforce a Quality of Service. It controls when each
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packets should be dequeued and transmitted, and can be used for
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limiting the data rate of a traffic class. To separate packets into
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traffic classes the user may choose
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.BR mqprio(8),
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and configure it like this:
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.EX
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# tc qdisc add dev eth0 handle 100: parent root mqprio num_tc 3 \\
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map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 \\
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queues 1@0 1@1 2@2 \\
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hw 0
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.EE
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.P
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To replace the current queueing discipline by ETF in traffic class
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number 0, issue:
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.P
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.EX
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# tc qdisc replace dev eth0 parent 100:1 etf \\
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clockid CLOCK_TAI delta 300000 offload
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.EE
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With the options above, etf will be configured to use CLOCK_TAI as
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its clockid_t, will schedule packets for 300 us before their txtime,
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and will enable the functionality on that in the network interface
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card. Deadline mode will not be configured for this mode.
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.SH AUTHORS
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Jesus Sanchez-Palencia <jesus.sanchez-palencia@intel.com>
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.br
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Vinicius Costa Gomes <vinicius.gomes@intel.com>
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