Manual: 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 configured through the delta option.

       The qdisc uses a rb-tree internally so packets are always 'ordered' by their txtime and will  be	 de‐
       queued 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 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 exam‐
       ple 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 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_get‐
	      time(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 trans‐
	      mission 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 con‐
	      trollers.	 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 schedule pack‐
       ets for 300 us before their txtime, and will enable the functionality on that in the  network  inter‐
       face card. Deadline mode will not be configured for this mode.

AUTHORS
       Jesus Sanchez-Palencia 
       Vinicius Costa Gomes 

iproute2					 05 Jul 2018					      ETF(8)