tc-etf

ETF(8)                               Linux                              ETF(8)

NAME
       ETF - Earliest TxTime First (ETF) Qdisc

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

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 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 con-
       figured through the 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 socket(7) for more  infor-
       mation.

       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 functional-
       ity that is commonly documented as "Launch Time" or "Time-Based  Sched-
       uling"  by  vendors  and  the  documentation  of network interface con-
       trollers.

       ETF is meant to be installed under another qdisc that maps packet flows
       to traffic classes, one example is mqprio(8).

PARAMETERS
       clockid
              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 clockid as the
              reference of their txtime timestamps. It will drop packets  com-
              ing from sockets that do not comply with that.

              For  more information about time and clocks on Linux, please re-
              fer to time(7) and clock_gettime(3).

       delta
              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 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.

       deadline_mode
              When 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
              etf(8)  will  set  the  txtime  of  the packet being dequeued to
              'now'.  The default is for this option to be disabled.

       offload
              When offload is set, 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.

       skip_sock_check
              etf(8)  currently  drops any packet which does not have a socket
              associated with it or if the  socket  does  not  have  SO_TXTIME
              socket  option set. But, this will not work if the launchtime is
              set by another entity inside the kernel (e.g. some other Qdisc).
              Setting  the skip_sock_check will skip checking for a socket as-
              sociated with the packet.

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 limit-
       ing the data rate of a traffic class. To separate packets into  traffic
       classes the user may choose 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 queueing discipline by ETF in traffic class num-
       ber 0, issue:

       # tc qdisc replace dev eth0 parent 100:1 etf \
            clockid CLOCK_TAI delta 300000 offload

       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.

AUTHORS
       Jesus Sanchez-Palencia <jesus.sanchez-palencia@intel.com>
       Vinicius Costa Gomes <vinicius.gomes@intel.com>

iproute2                          05 Jul 2018                           ETF(8)