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 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  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 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 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 <jesus.sanchez-palencia@intel.com>
       Vinicius Costa Gomes <vinicius.gomes@intel.com>