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 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
       information.

       The  etf	 qdisc	will  drop any packets with a txtime in the past, or if a packet expires while waiting for being de‐
       queued.

       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 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 time‐
	      stamps. 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 mi‐
	      nus 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 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 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 
       Vinicius Costa Gomes 

iproute2						 05 Jul 2018						      ETF(8)