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4712a46174
Since this feature's introduction in commit 9c66d1564676 ("taprio: Add
support for hardware offloading") from kernel v5.4, it never got
documented in the man pages. Due to this reason, we see customer reports
of seemingly contradictory information: the community manpages claim
there is no support for full offload, nonetheless many silicon vendors
have already implemented it.
This patch documents the full offload feature (enabled by specifying
"flags 2" to the taprio qdisc) and gives one more example that tries to
illustrate some of the finer points related to the usage.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
224 lines
6.3 KiB
Groff
224 lines
6.3 KiB
Groff
.TH TAPRIO 8 "25 Sept 2018" "iproute2" "Linux"
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.SH NAME
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TAPRIO \- Time Aware Priority Shaper
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.SH SYNOPSIS
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.B tc qdisc ... dev
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dev
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.B parent
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classid
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.B [ handle
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major:
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.B ] taprio num_tc
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tcs
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.ti +8
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.B map
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P0 P1 P2 ...
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.B queues
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count1@offset1 count2@offset2 ...
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.ti +8
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.B base-time
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base-time
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.B clockid
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clockid
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.ti +8
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.B sched-entry
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<command 1> <gate mask 1> <interval 1>
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.ti +8
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.B sched-entry
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<command 2> <gate mask 2> <interval 2>
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.ti +8
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.B sched-entry
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<command 3> <gate mask 3> <interval 3>
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.ti +8
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.B sched-entry
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<command N> <gate mask N> <interval N>
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.SH DESCRIPTION
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The TAPRIO qdisc implements a simplified version of the scheduling
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state machine defined by IEEE 802.1Q-2018 Section 8.6.9, which allows
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configuration of a sequence of gate states, where each gate state
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allows outgoing traffic for a subset (potentially empty) of traffic
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classes.
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How traffic is mapped to different hardware queues is similar to
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.BR mqprio(8)
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and so the
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.B map
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and
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.B queues
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parameters have the same meaning.
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The other parameters specify the schedule, and at what point in time
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it should start (it can behave as the schedule started in the past).
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.SH PARAMETERS
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.TP
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num_tc
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.BR
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Number of traffic classes to use. Up to 16 classes supported.
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.TP
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map
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.br
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The priority to traffic class map. Maps priorities 0..15 to a specified
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traffic class. See
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.BR mqprio(8)
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for more details.
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.TP
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queues
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.br
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Provide count and offset of queue range for each traffic class. In the
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format,
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.B count@offset.
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Queue ranges for each traffic classes cannot overlap and must be a
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contiguous range of queues.
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.TP
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base-time
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.br
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Specifies the instant in nanoseconds, using the reference of
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.B clockid,
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defining the time when the schedule starts. If 'base-time' is a time
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in the past, the schedule will start at
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base-time + (N * cycle-time)
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where N is the smallest integer so the resulting time is greater than
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"now", and "cycle-time" is the sum of all the intervals of the entries
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in the schedule;
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.TP
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clockid
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.br
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Specifies the clock to be used by qdisc's internal timer for measuring
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time and scheduling events. This argument must be omitted when using the
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full-offload feature (flags 0x2), since in that case, the clockid is
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implicitly /dev/ptpN (where N is given by
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.B ethtool -T eth0 | grep 'PTP Hardware Clock'
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), and therefore not necessarily synchronized with the system's CLOCK_TAI.
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.TP
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sched-entry
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.br
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There may multiple
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.B sched-entry
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parameters in a single schedule. Each one has the
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sched-entry <command> <gatemask> <interval>
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format. The only supported <command> is "S", which
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means "SetGateStates", following the IEEE 802.1Q-2018 definition
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(Table 8-7). <gate mask> is a bitmask where each bit is a associated
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with a traffic class, so bit 0 (the least significant bit) being "on"
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means that traffic class 0 is "active" for that schedule entry.
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<interval> is a time duration, in nanoseconds, that specifies for how
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long that state defined by <command> and <gate mask> should be held
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before moving to the next entry.
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.TP
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flags
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.br
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This is a bit mask which specifies different modes for taprio.
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.RS
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.TP
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.I 0x1
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Enables the txtime-assist feature. In this mode, taprio will set the transmit
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timestamp depending on the interval in which the packet needs to be
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transmitted. It will then utililize the
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.BR etf(8)
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qdisc to sort and transmit the packets at the right time. The second example
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can be used as a reference to configure this mode.
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.TP
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.I 0x2
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Enables the full-offload feature. In this mode, taprio will pass the gate
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control list to the NIC which will execute it cyclically in hardware.
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When using full-offload, there is no need to specify the
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.B clockid
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argument.
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The txtime-assist and full-offload features are mutually exclusive, i.e.
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setting flags to 0x3 is invalid.
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.RE
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.TP
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txtime-delay
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.br
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This parameter is specific to the txtime offload mode. It specifies the maximum
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time a packet might take to reach the network card from the taprio qdisc. The
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value should always be greater than the delta specified in the
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.BR etf(8)
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qdisc.
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.SH EXAMPLES
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The following example shows how an traffic schedule with three traffic
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classes ("num_tc 3"), which are separated different traffic classes,
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we are going to call these TC 0, TC 1 and TC 2. We could read the
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"map" parameter below as: traffic with priority 3 is classified as TC
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0, priority 2 is classified as TC 1 and the rest is classified as TC
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2.
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The schedule will start at instant 1528743495910289987 using the
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reference CLOCK_TAI. The schedule is composed of three entries each of
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300us duration.
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.EX
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# tc qdisc replace dev eth0 parent root handle 100 taprio \\
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num_tc 3 \\
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map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 \\
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queues 1@0 1@1 2@2 \\
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base-time 1528743495910289987 \\
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sched-entry S 01 300000 \\
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sched-entry S 02 300000 \\
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sched-entry S 04 300000 \\
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clockid CLOCK_TAI
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.EE
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Following is an example to enable the txtime offload mode in taprio. See
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.BR etf(8)
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for more information about configuring the ETF qdisc.
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.EX
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# tc qdisc replace dev eth0 parent root handle 100 taprio \\
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num_tc 3 \\
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map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 \\
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queues 1@0 1@0 1@0 \\
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base-time 1528743495910289987 \\
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sched-entry S 01 300000 \\
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sched-entry S 02 300000 \\
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sched-entry S 04 400000 \\
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flags 0x1 \\
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txtime-delay 200000 \\
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clockid CLOCK_TAI
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# tc qdisc replace dev $IFACE parent 100:1 etf skip_skb_check \\
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offload delta 200000 clockid CLOCK_TAI
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.EE
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The following is a schedule in full offload mode. The
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.B base-time
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is 200 ns and the
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.B cycle-time
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is implicitly calculated as the sum of all
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.B sched-entry
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durations (i.e. 20 us + 20 us + 60 us = 100 us). Although the base-time is in
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the past, the hardware will start executing the schedule at a PTP time equal to
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the smallest integer multiple of 100 us, plus 200 ns, that is larger than the
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NIC's current PTP time.
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.EX
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# tc qdisc add dev eth0 parent root taprio \\
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num_tc 8 \\
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map 0 1 2 3 4 5 6 7 \\
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queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 \\
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base-time 200 \\
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sched-entry S 80 20000 \\
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sched-entry S a0 20000 \\
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sched-entry S df 60000 \\
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flags 0x2
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.EE
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.SH AUTHORS
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Vinicius Costa Gomes <vinicius.gomes@intel.com>
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