tc-taprio(8) — Linux manual page


TAPRIO(8)                         Linux                        TAPRIO(8)

NAME         top

       TAPRIO - Time Aware Priority Shaper

SYNOPSIS         top

       tc qdisc ... dev dev parent classid [ handle major: ] taprio
       num_tc tcs
               map P0 P1 P2 ...  queues count1@offset1 count2@offset2
               base-time base-time clockid clockid
               sched-entry <command 1> <gate mask 1> <interval 1>
               sched-entry <command 2> <gate mask 2> <interval 2>
               sched-entry <command 3> <gate mask 3> <interval 3>
               sched-entry <command N> <gate mask N> <interval N>
               [ max-sdu <queueMaxSDU[TC 0]> <queueMaxSDU[TC 1]>
       <queueMaxSDU[TC N]> ]
               [ fp <adminStatus[TC 0]> <adminStatus[TC 1]>
       <adminStatus[TC N]> ]

DESCRIPTION         top

       The TAPRIO qdisc implements a simplified version of the
       scheduling state machine defined by IEEE 802.1Q-2018 Section
       8.6.9, which allows configuration of a sequence of gate states,
       where each gate state allows outgoing traffic for a subset
       (potentially empty) of traffic classes.

       How traffic is mapped to different hardware queues is similar to
       mqprio(8) and so the map and queues parameters have the same

       The other parameters specify the schedule, and at what point in
       time it should start (it can behave as the schedule started in
       the past).

PARAMETERS         top

       num_tc Number of traffic classes to use. Up to 16 classes

              The priority to traffic class map. Maps priorities 0..15
              to a specified traffic class. See mqprio(8) for more

              Provide count and offset of queue range for each traffic
              class. In the format, count@offset.  Queue ranges for each
              traffic classes cannot overlap and must be a contiguous
              range of queues.

              Specifies the instant in nanoseconds, using the reference
              of clockid, defining the time when the schedule starts. If
              'base-time' is a time in the past, the schedule will start

              base-time + (N * cycle-time)

              where N is the smallest integer so the resulting time is
              greater than "now", and "cycle-time" is the sum of all the
              intervals of the entries in the schedule;

              Specifies the clock to be used by qdisc's internal timer
              for measuring time and scheduling events. This argument
              must be omitted when using the full-offload feature (flags
              0x2), since in that case, the clockid is implicitly
              /dev/ptpN (where N is given by ethtool -T eth0 | grep 'PTP
              Hardware Clock' ), and therefore not necessarily
              synchronized with the system's CLOCK_TAI.

              There may multiple sched-entry parameters in a single
              schedule. Each one has the

              sched-entry <command> <gatemask> <interval>

              format. The only supported <command> is "S", which means
              "SetGateStates", following the IEEE 802.1Q-2018 definition
              (Table 8-7). <gate mask> is a bitmask where each bit is a
              associated with a traffic class, so bit 0 (the least
              significant bit) being "on" means that traffic class 0 is
              "active" for that schedule entry.  <interval> is a time
              duration, in nanoseconds, that specifies for how long that
              state defined by <command> and <gate mask> should be held
              before moving to the next entry.

              This is a bit mask which specifies different modes for

              0x1    Enables the txtime-assist feature. In this mode,
                     taprio will set the transmit timestamp depending on
                     the interval in which the packet needs to be
                     transmitted. It will then utililize the etf(8)
                     qdisc to sort and transmit the packets at the right
                     time. The second example can be used as a reference
                     to configure this mode.

              0x2    Enables the full-offload feature. In this mode,
                     taprio will pass the gate control list to the NIC
                     which will execute it cyclically in hardware.  When
                     using full-offload, there is no need to specify the
                     clockid argument.

                     The txtime-assist and full-offload features are
                     mutually exclusive, i.e.  setting flags to 0x3 is

              This parameter is specific to the txtime offload mode. It
              specifies the maximum time a packet might take to reach
              the network card from the taprio qdisc. The value should
              always be greater than the delta specified in the etf(8)

              Specifies an array containing at most 16 elements, one per
              traffic class, which corresponds to the queueMaxSDU table
              from IEEE 802.1Q-2018. Each array element represents the
              maximum L2 payload size that can egress that traffic
              class.  Elements that are not filled in default to 0. The
              value 0 means that the traffic class can send packets up
              to the port's maximum MTU in size.

              Selects whether traffic classes are express or
              preemptible. See tc-mqprio(8) for details.

EXAMPLES         top

       The following example shows how an traffic schedule with three
       traffic classes ("num_tc 3"), which are separated different
       traffic classes, we are going to call these TC 0, TC 1 and TC 2.
       We could read the "map" parameter below as: traffic with priority
       3 is classified as TC 0, priority 2 is classified as TC 1 and the
       rest is classified as TC 2.

       The schedule will start at instant 1528743495910289987 using the
       reference CLOCK_TAI. The schedule is composed of three entries
       each of 300us duration.

       # tc qdisc replace dev eth0 parent root handle 100 stab overhead 24 taprio \
                     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 \
                     base-time 1528743495910289987 \
                     sched-entry S 01 300000 \
                     sched-entry S 02 300000 \
                     sched-entry S 04 300000 \
                     clockid CLOCK_TAI

       Following is an example to enable the txtime offload mode in
       taprio. See etf(8) for more information about configuring the ETF

       # tc qdisc replace dev eth0 parent root handle 100 stab overhead 24 taprio \
                     num_tc 3 \
                     map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 \
                     queues 1@0 1@0 1@0 \
                     base-time 1528743495910289987 \
                     sched-entry S 01 300000 \
                     sched-entry S 02 300000 \
                     sched-entry S 04 400000 \
                     flags 0x1 \
                     txtime-delay 200000 \
                     clockid CLOCK_TAI

       # tc qdisc replace dev $IFACE parent 100:1 etf skip_skb_check \
                     offload delta 200000 clockid CLOCK_TAI

       The following is a schedule in full offload mode. The base-time
       is 200 ns and the cycle-time is implicitly calculated as the sum
       of all sched-entry durations (i.e. 20 us + 20 us + 60 us = 100
       us). Although the base-time is in the past, the hardware will
       start executing the schedule at a PTP time equal to the smallest
       integer multiple of 100 us, plus 200 ns, that is larger than the
       NIC's current PTP time. In addition, the MTU for traffic class 5
       is limited to 200 octets, so that the interference this creates
       upon traffic class 7 during the time window when their gates are
       both open is bounded. The interference is determined by the
       transmit time of the max SDU, plus the L2 header length, plus the
       L1 overhead (determined from the size table specified using

       # tc qdisc add dev eth0 parent root stab overhead 24 taprio \
                     num_tc 8 \
                     map 0 1 2 3 4 5 6 7 \
                     queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 \
                     max-sdu 0 0 0 0 0 200 0 0 \
                     base-time 200 \
                     sched-entry S 80 20000 \
                     sched-entry S a0 20000 \
                     sched-entry S 5f 60000 \
                     flags 0x2

SEE ALSO         top


AUTHORS         top

       Vinicius Costa Gomes <>

COLOPHON         top

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iproute2                      25 Sept 2018                     TAPRIO(8)