phpman > man > tc-etf(8)

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 configured 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 con‐
       figure 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 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) applica‐
       tions, 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 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 sched‐
              uling 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 coming from
              sockets that do not comply with that.

              For more information about time and clocks on  Linux,  please  refer  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 dur‐
              ing 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  re‐
              ferred  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 associated 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 limiting 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 number 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 sched‐
       ule  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 AT intel.com>
       Vinicius Costa Gomes <vinicius.gomes AT intel.com>



iproute2                                     05 Jul 2018                                      ETF(8)