1ETF(8)                               Linux                              ETF(8)
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NAME

6       ETF - Earliest TxTime First (ETF) Qdisc
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SYNOPSIS

9       tc  qdisc  ...  dev  dev  parent  classid [ handle major: ] etf clockid
10       clockid [ delta delta_nsecs ] [ deadline_mode ] [ offload ]
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DESCRIPTION

14       The ETF (Earliest TxTime First) qdisc allows  applications  to  control
15       the  instant  when a packet should be dequeued from the traffic control
16       layer into the netdevice. If offload is configured and supported by the
17       network interface card, the it will also control when packets leave the
18       network controller.
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20       ETF achieves that by buffering packets until a configurable time before
21       their  transmission  time (i.e. txtime, or deadline), which can be con‐
22       figured through the delta option.
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24       The qdisc uses a rb-tree internally so packets are always 'ordered'  by
25       their  txtime and will be dequeued following the (next) earliest txtime
26       first.
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28       It relies on the SO_TXTIME socket option and  the  SCM_TXTIME  CMSG  in
29       each  packet field to configure the behavior of time dependent sockets:
30       the clockid to be used as a reference, if the expected mode  of  txtime
31       for  that socket is deadline or strict mode, and if packet drops should
32       be reported on the socket's error queue. See socket(7) for more  infor‐
33       mation.
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35       The  etf qdisc will drop any packets with a txtime in the past, or if a
36       packet expires while waiting for being dequeued.
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38       This queueing discipline is intended to be used by TSN (Time  Sensitive
39       Networking)  applications, and it exposes a traffic shaping functional‐
40       ity that is commonly documented as "Launch Time" or "Time-Based  Sched‐
41       uling"  by  vendors  and  the  documentation  of network interface con‐
42       trollers.
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44       ETF is meant to be installed under another qdisc that maps packet flows
45       to traffic classes, one example is mqprio(8).
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PARAMETERS

49       clockid
50              Specifies  the  clock  to  be used by qdisc's internal timer for
51              measuring time and scheduling events.  The  qdisc  expects  that
52              packets  passing through it to be using this same clockid as the
53              reference of their txtime timestamps. It will drop packets  com‐
54              ing from sockets that do not comply with that.
55
56              For  more  information  about  time  and clocks on Linux, please
57              refer to time(7) and clock_gettime(3).
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60       delta
61              After enqueueing or dequeueing a packet, the qdisc will schedule
62              its  next  wake-up  time  for  the  next txtime minus this delta
63              value.  This means delta can be used as a fudge factor  for  the
64              scheduler  latency of a system.  This value must be specified in
65              nanoseconds.  The default value is 0 nanoseconds.
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68       deadline_mode
69              When deadline_mode is set, the qdisc will handle txtime  with  a
70              different  semantics,  changed from a 'strict' transmission time
71              to a deadline.  In practice, this means during the dequeue  flow
72              etf(8)  will  set  the  txtime  of  the packet being dequeued to
73              'now'.  The default is for this option to be disabled.
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76       offload
77              When offload is set, etf(8) will try to  configure  the  network
78              interface  so  time-based transmission arbitration is enabled in
79              the controller. This feature is commonly referred to as  "Launch
80              Time" or "Time-Based Scheduling" by the documentation of network
81              interface controllers.  The default is for  this  option  to  be
82              disabled.
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EXAMPLES

86       ETF  is  used  to  enforce  a Quality of Service. It controls when each
87       packets should be dequeued and transmitted, and can be used for  limit‐
88       ing  the data rate of a traffic class. To separate packets into traffic
89       classes the user may choose mqprio(8), and configure it like this:
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91       # tc qdisc add dev eth0 handle 100: parent root mqprio num_tc 3 \
92            map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 \
93            queues 1@0 1@1 2@2 \
94            hw 0
95
96       To replace the current queueing discipline by ETF in traffic class num‐
97       ber 0, issue:
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99       # tc qdisc replace dev eth0 parent 100:1 etf \
100            clockid CLOCK_TAI delta 300000 offload
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102       With  the options above, etf will be configured to use CLOCK_TAI as its
103       clockid_t, will schedule packets for 300 us before  their  txtime,  and
104       will  enable  the  functionality on that in the network interface card.
105       Deadline mode will not be configured for this mode.
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AUTHORS

109       Jesus Sanchez-Palencia <jesus.sanchez-palencia@intel.com>
110       Vinicius Costa Gomes <vinicius.gomes@intel.com>
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114iproute2                          05 Jul 2018                           ETF(8)
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