TAPRIO

Section: Linux (8)
Updated: 25 Sept 2018
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NAME

TAPRIO - Time Aware Priority Shaper  

SYNOPSIS

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

 

DESCRIPTION

The TAPRIO qdisc implements a simplified version of the scheduling state machine defined by IEEE 802.1-2018 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 meaning.

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

num_tc

Numberoftrafficclassestouse.Upto16classessupported.

map

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

queues

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.

bas-time

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

bas-time + (N * cycl-time)

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

clockid

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 ful-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.

sche-entry

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

sche-entry <command> <gatemask> <interval>

format.

<command> support the following values:
S for SetGateStates
H for Se-An-Hol-MAC
R for Se-An-Releas-MAC
These commands follow the IEEE 802.1-2018 definition (Table -7).

<gate mask> is a bitmask where each bit is 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.

flags

This is a bit mask which specifies different modes for taprio.

0x1

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

The txtim-assist and ful-offload features are mutually exclusive, i.e. setting flags to 0x3 is invalid.

txtim-delay

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) qdisc.

ma-sdu

Specifies an array containing at most 16 elements, one per traffic class, which corresponds to the queueMaxSDU table from IEEE 802.1-2018. 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.

fp

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

 

EXAMPLES

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 
              bas-time 1528743495910289987 
              sche-entry S 01 300000 
              sche-entry S 02 300000 
              sche-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 qdisc.

# 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 
              bas-time 1528743495910289987 
              sche-entry S 01 300000 
              sche-entry S 02 300000 
              sche-entry S 04 400000 
              flags 0x1 
              txtim-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 bas-time is 200 ns and the cycl-time is implicitly calculated as the sum of all sche-entry durations (i.e. 20 us + 20 us + 60 us = 100 us). Although the bas-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 t-stab(8)).

# 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 
              ma-sdu 0 0 0 0 0 200 0 0 
              bas-time 200 
              sche-entry S 80 20000 
              sche-entry S a0 20000 
              sche-entry S 5f 60000 
              flags 0x2

 

SEE ALSO

t-stab(8)

 

AUTHORS

Vinicius Costa Gomes <vinicius.gomes@intel.com>

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Index

NAME

SYNOPSIS

DESCRIPTION

PARAMETERS

EXAMPLES

SEE ALSO

AUTHORS