• Each "deadline delta" is calculated as the difference between the timestamp and the scheduled TX time of this packet. The
HW TX deadline delta should always be negative, as that indicates the packets were sent before the scheduled TX time has
expired. The SW TX timestamps are taken after the HW TX timestamps in this case, so their meaning is less relevant for
this driver. The RX deadline deltas will become relevant once the 802.1Qbv schedule is installed on the sja1105 switch port.
The above log was taken with no 802.1Qbv schedule active on the sja1105 port and no background traffic. After starting
background traffic:
# Host 2
iperf3 -s > /dev/null &
sysctl -w kernel.sched_rt_runtime_us=-1
chrt --fifo 90 isochron rcv -i eth0 --quiet
# Host 3
ip addr add 192.168.1.3/24 dev eth0
iperf3 -c 192.168.1.2 -t 48600
Connecting to host 10.0.0.112, port 5201
[ 5] local 10.0.0.113 port 60360 connected to 10.0.0.112 port 5201
[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.00 sec 105 MBytes 878 Mbits/sec 0 489 KBytes
[ 5] 1.00-2.00 sec 102 MBytes 859 Mbits/sec 0 513 KBytes
[ 5] 2.00-3.00 sec 102 MBytes 858 Mbits/sec 0 513 KBytes
[ 5] 3.00-4.00 sec 101 MBytes 851 Mbits/sec 0 513 KBytes
[ 5] 4.00-5.00 sec 102 MBytes 860 Mbits/sec 0 539 KBytes
a re-run of the isochron traffic generated by Host 1 looks as follows:
chrt --fifo 90 isochron send -i eno0 -d 00:04:9f:05:de:06 -p 6 -v 0 -b 0 -S 50000 -c 400000 -a 90000 -
n 10000 -s 64 -C 10.0.0.112 -q
Base time 0.000040000 is in the past, winding it into the future
Now: 1586286409.635121693
Base time: 1586286409.635160000
Cycle time: 0.000400000
Collecting receiver stats
Summary:
Path delay: min 4314 max 16774 mean 9725.688 stddev 3919.150
HW TX deadline delta: min -64273 max -8538 mean -59894.931 stddev 1467.284
SW TX deadline delta: min -33286 max 37575 mean -28498.114 stddev 2006.546
HW RX deadline delta: min -58924 max -904 mean -50169.243 stddev 4183.042
SW RX deadline delta: min -52757 max 1109472 mean -29436.032 stddev 23537.847
HW TX deadline misses: 0 (0.000%)
SW TX deadline misses: 4 (0.040%)
It can be seen that the path delay variance has increased due to the prolonged wait of packets until MTU-sized packets generated
by iperf3 have finished transmission.
Finally, installing the 802.1Qbv schedule on the switch has effects upon all statistics calculated by isochron:
chrt --fifo 90 isochron send -i eno0 -d 00:04:9f:05:de:06 -p 6 -v 0 -b 0 -S 50000 -c 400000 -a 90000 -
n 10000 -s 64 -C 10.0.0.112 -q
Base time 0.000040000 is in the past, winding it into the future
Now: 1586286689.223100936
Base time: 1586286689.223160000
Cycle time: 0.000400000
Collecting receiver stats
Summary:
Path delay: min 14199 max 65684 mean 61357.368 stddev 1494.831
HW TX deadline delta: min -64128 max -12643 mean -59822.445 stddev 1494.557
SW TX deadline delta: min -33616 max 25621 mean -28448.709 stddev 1974.185
HW RX deadline delta: min 1476 max 2041 mean 1534.924 stddev 24.822
SW RX deadline delta: min 5243 max 1122800 mean 21040.814 stddev 16752.155
NXP Semiconductors
TSN
Open Industrial User Guide, Rev. 1.8, 05/2020
User's Guide
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