TAPRIO(8) Linux TAPRIO(8)
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 ...
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>
DESCRIPTION
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 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 Number of traffic classes to use. Up to 16 classes supported.
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.
base-time
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 at
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;
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 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.
sched-entry
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 "Set-
GateStates", 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.
flags
This is a bit mask which specifies different modes for taprio.
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 pack-
ets 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-off-
load, 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 invalid.
txtime-delay
This parameter is specific to the txtime offload mode. It speci-
fies 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.
max-sdu
Specifies an array containing at most 16 elements, one per traf-
fic class, which corresponds to the queueMaxSDU table from IEEE
802.1Q-2018. Each array element represents the maximum L2 pay-
load 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.
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, pri-
ority 2 is classified as TC 1 and the rest is classified as TC 2.
The schedule will start at instant 1528743495910289987 using the refer-
ence CLOCK_TAI. The schedule is composed of three entries each of 300us
duration.
# tc qdisc replace dev eth0 parent root handle 100 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 qdisc.
# tc qdisc replace dev eth0 parent root handle 100 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 sched-
ule 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 addi-
tion, 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 deter-
mined by the transmit time of the max SDU, plus the L2 header length,
plus the L1 overhead.
# tc qdisc add dev eth0 parent root 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
AUTHORS
Vinicius Costa Gomes <vinicius.gomes AT intel.com>
iproute2 25 Sept 2018 TAPRIO(8)
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