1TAPRIO(8) Linux TAPRIO(8)
2
6 TAPRIO - Time Aware Priority Shaper
7
9 tc qdisc ... dev dev parent classid [ handle major: ] taprio num_tc tcs
10 map P0 P1 P2 ... queues count1@offset1 count2@offset2 ...
11 base-time base-time clockid clockid
12 sched-entry <command 1> <gate mask 1> <interval 1>
13 sched-entry <command 2> <gate mask 2> <interval 2>
14 sched-entry <command 3> <gate mask 3> <interval 3>
15 sched-entry <command N> <gate mask N> <interval N>
16 [ max-sdu <queueMaxSDU[TC 0]> <queueMaxSDU[TC 1]> <queue‐
17 MaxSDU[TC N]> ]
18 [ fp <adminStatus[TC 0]> <adminStatus[TC 1]> <adminStatus[TC
19 N]> ]
20
23 The TAPRIO qdisc implements a simplified version of the scheduling
24 state machine defined by IEEE 802.1Q-2018 Section 8.6.9, which allows
25 configuration of a sequence of gate states, where each gate state al‐
26 lows outgoing traffic for a subset (potentially empty) of traffic
27 classes.
28 How traffic is mapped to different hardware queues is similar to
30 mqprio(8) and so the map and queues parameters have the same meaning.
31 The other parameters specify the schedule, and at what point in time it
33 should start (it can behave as the schedule started in the past).
34
37 num_tc Number of traffic classes to use. Up to 16 classes supported.
38 map
41 The priority to traffic class map. Maps priorities 0..15 to a
42 specified traffic class. See mqprio(8) for more details.
43 queues
46 Provide count and offset of queue range for each traffic class.
47 In the format, count@offset. Queue ranges for each traffic
48 classes cannot overlap and must be a contiguous range of queues.
49 base-time
52 Specifies the instant in nanoseconds, using the reference of
53 clockid, defining the time when the schedule starts. If 'base-
54 time' is a time in the past, the schedule will start at
55 base-time + (N * cycle-time)
57 where N is the smallest integer so the resulting time is greater
59 than "now", and "cycle-time" is the sum of all the intervals of
60 the entries in the schedule;
61 clockid
64 Specifies the clock to be used by qdisc's internal timer for
65 measuring time and scheduling events. This argument must be
66 omitted when using the full-offload feature (flags 0x2), since
67 in that case, the clockid is implicitly /dev/ptpN (where N is
68 given by ethtool -T eth0 | grep 'PTP Hardware Clock' ), and
69 therefore not necessarily synchronized with the system's
70 CLOCK_TAI.
71 sched-entry
74 There may multiple sched-entry parameters in a single schedule.
75 Each one has the
76 sched-entry <command> <gatemask> <interval>
78 format. The only supported <command> is "S", which means "Set‐
80 GateStates", following the IEEE 802.1Q-2018 definition (Table
81 8-7). <gate mask> is a bitmask where each bit is a associated
82 with a traffic class, so bit 0 (the least significant bit) being
83 "on" means that traffic class 0 is "active" for that schedule
84 entry. <interval> is a time duration, in nanoseconds, that
85 specifies for how long that state defined by <command> and <gate
86 mask> should be held before moving to the next entry.
87 flags
90 This is a bit mask which specifies different modes for taprio.
91 0x1 Enables the txtime-assist feature. In this mode, taprio
93 will set the transmit timestamp depending on the interval
94 in which the packet needs to be transmitted. It will then
95 utililize the etf(8) qdisc to sort and transmit the pack‐
96 ets at the right time. The second example can be used as
97 a reference to configure this mode.
98 0x2 Enables the full-offload feature. In this mode, taprio
100 will pass the gate control list to the NIC which will ex‐
101 ecute it cyclically in hardware. When using full-off‐
102 load, there is no need to specify the clockid argument.
103 The txtime-assist and full-offload features are mutually
105 exclusive, i.e. setting flags to 0x3 is invalid.
106 txtime-delay
109 This parameter is specific to the txtime offload mode. It speci‐
110 fies the maximum time a packet might take to reach the network
111 card from the taprio qdisc. The value should always be greater
112 than the delta specified in the etf(8) qdisc.
113 max-sdu
116 Specifies an array containing at most 16 elements, one per traf‐
117 fic class, which corresponds to the queueMaxSDU table from IEEE
118 802.1Q-2018. Each array element represents the maximum L2 pay‐
119 load size that can egress that traffic class. Elements that are
120 not filled in default to 0. The value 0 means that the traffic
121 class can send packets up to the port's maximum MTU in size.
122 fp
125 Selects whether traffic classes are express or preemptible. See
126 tc-mqprio(8) for details.
127
130 The following example shows how an traffic schedule with three traffic
131 classes ("num_tc 3"), which are separated different traffic classes, we
132 are going to call these TC 0, TC 1 and TC 2. We could read the "map"
133 parameter below as: traffic with priority 3 is classified as TC 0, pri‐
134 ority 2 is classified as TC 1 and the rest is classified as TC 2.
135 The schedule will start at instant 1528743495910289987 using the refer‐
137 ence CLOCK_TAI. The schedule is composed of three entries each of 300us
138 duration.
139 # tc qdisc replace dev eth0 parent root handle 100 stab overhead 24 taprio \
141 num_tc 3 \
142 map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 \
143 queues 1@0 1@1 2@2 \
144 base-time 1528743495910289987 \
145 sched-entry S 01 300000 \
146 sched-entry S 02 300000 \
147 sched-entry S 04 300000 \
148 clockid CLOCK_TAI
149 Following is an example to enable the txtime offload mode in taprio.
151 See etf(8) for more information about configuring the ETF qdisc.
152 # tc qdisc replace dev eth0 parent root handle 100 stab overhead 24 taprio \
154 num_tc 3 \
155 map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 \
156 queues 1@0 1@0 1@0 \
157 base-time 1528743495910289987 \
158 sched-entry S 01 300000 \
159 sched-entry S 02 300000 \
160 sched-entry S 04 400000 \
161 flags 0x1 \
162 txtime-delay 200000 \
163 clockid CLOCK_TAI
164 # tc qdisc replace dev $IFACE parent 100:1 etf skip_skb_check \
166 offload delta 200000 clockid CLOCK_TAI
167 The following is a schedule in full offload mode. The base-time is 200
169 ns and the cycle-time is implicitly calculated as the sum of all sched-
170 entry durations (i.e. 20 us + 20 us + 60 us = 100 us). Although the
171 base-time is in the past, the hardware will start executing the sched‐
172 ule at a PTP time equal to the smallest integer multiple of 100 us,
173 plus 200 ns, that is larger than the NIC's current PTP time. In addi‐
174 tion, the MTU for traffic class 5 is limited to 200 octets, so that the
175 interference this creates upon traffic class 7 during the time window
176 when their gates are both open is bounded. The interference is deter‐
177 mined by the transmit time of the max SDU, plus the L2 header length,
178 plus the L1 overhead (determined from the size table specified using
179 tc-stab(8)).
180 # tc qdisc add dev eth0 parent root stab overhead 24 taprio \
182 num_tc 8 \
183 map 0 1 2 3 4 5 6 7 \
184 queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 \
185 max-sdu 0 0 0 0 0 200 0 0 \
186 base-time 200 \
187 sched-entry S 80 20000 \
188 sched-entry S a0 20000 \
189 sched-entry S 5f 60000 \
190 flags 0x2
191
194 tc-stab(8)
195
198 Vinicius Costa Gomes <vinicius.gomes@intel.com>
199iproute2 25 Sept 2018 TAPRIO(8)