Provided by: isochron_0.9-0.2_amd64 
NAME
isochron-report - Gather statistics from logged isochron data
SYNOPSIS
isochron report [OPTIONS]
DESCRIPTION
This command opens an isochron.dat file generated by isochron send and filters the requested data from
it.
OPTIONS
-h, --help
prints the short help message and exits
-F, --input-file <PATH>
specify the path to the input file. Optional, defaults to “isochron.dat”.
-m, --summary
optionally calculate and print a summary of the built-in metrics.
-s, --start <NUMBER>
specify the sequence number of the first packet to be taken into consideration for printing and
for statistics calculation. Optional; defaults to sequence number 1 (the first packet).
-S, --stop <NUMBER>
specify the sequence number of the last packet to be taken into consideration for printing and for
statistics calculation. Optional; defaults to a sequence number equal to the number of packets of
the test (the last packet).
-f, --printf-format <STRING>
specify the format in which a packet will be printed. Optional; if not specified, per-packet
information is not printed.
-a, --printf-args <STRING>
specify the built-in variables which will be printed per packet.
PRINTF FORMAT
The --printf-format argument specifies a free-form string that can also contain up to 256 printf-like
codes prefixed by the % (percent) character. The printf codes will be replaced by isochron for each
packet with internal variables taken from the log. The newline character is not added automatically
between packets.
The printf codes understood by isochron are:
%d print a built-in variable as a signed integer in decimal format.
%u print a built-in variable as an unsigned integer in decimal format.
%x print a built-in variable as an unsigned integer in hexadecimal format.
%T print a built-in variable in human-readable time format (sec.nsec).
PRINTF VARIABLES
The --printf-args argument is an array of single-character isochron variable codes. The program
associates, in left-to-right order, each variable code with the printf code from the format specifier in
order to figure out how to print it.
The variable codes understood by isochron are:
A advance time as defined by isochron send --advance-time. Can be printed using %d, %u, %x or %T.
B base time as defined by isochron send --base-time, then adjusted by the sender application using
the shift time and advanced into the immediate future at the time of the test. The base time
minus the advance time denotes the programmed time of the wakeup timer for the sender’s first
packet. Can be printed using %d, %u, %x or %T.
C cycle time as defined by isochron send --cycle-time. Can be printed using %d, %u, %x or %T.
H shift time as defined by isochron send --shift-time. Can be printed using %d, %u, %x or %T.
W window size as defined by isochron send --window-size. Can be printed using %d, %u, %x or %T.
S scheduled TX time of the packet (the time at which the packet must hit the wire). Can be printed
using %d, %u, %x or %T.
w the actual value of the CLOCK_TAI system clock when the sender starts executing code again
immediately after its wakeup timer for the packet has expired. Can be printed using %d, %u, %x or
%T.
T TX hardware timestamp of the packet, taken by the NIC of the sender. Can be printed using %d, %u,
%x or %T.
t TX software timestamp of the packet, taken by the NIC driver of the sender right before hardware
transmission. Can be printed using %d, %u, %x or %T.
s TX software timestamp of the packet, taken by the network stack prior to entering the packet
scheduler (qdisc). Can be printed using %d, %u, %x or %T.
q sequence number of the packet, starting from 1. Can be printed using %u or %x.
a the arrival time of the packet, i.e. the actual value of the CLOCK_TAI system clock when the
receiver starts executing code again immediately after fully receiving the packet. Can be printed
using %d, %u, %x or %T.
R RX hardware timestamp of the packet, taken by the NIC of the receiver. Can be printed using %d,
%u, %x or %T.
r RX software timestamp of the packet, taken by the NIC driver right after reception from hardware.
Can be printed using %d, %u, %x or %T.
BUILT-IN METRICS
When running with the --summary option, isochron defines some latency related metrics and calculates the
following statistics on them: maximum value, minimum value, packet sequence number associated with the
min and max, mean value, standard deviation.
The built-in metrics are:
Path delay
R - T (HW TX timestamp to HW RX timestamp)
Sender latency
t - w (actual sender wakeup time to SW TX timestamp)
MAC latency
T - S (scheduled TX time to HW TX timestamp)
Application latency budget (“time to spare per cycle”)
S - T (time until HW TX timestamp would exceed scheduled TX time)
Wakeup latency
w - (S - A) (programmed wakeup time, i.e. scheduled TX time minus advance time, to actual wakeup
time)
Driver latency (actually driver + qdisc latency)
t - s (pre-qdisc timestamp to driver-level software TX timestamp)
Arrival latency
a - R (HW RX timestamp to application)
Notice how the “MAC latency” and the “Application latency budget” is the same metric, but calculated in
reverse. The data is interpreted by the application depending on whether the hardware was expected to
send the packet right away, or queue it until the scheduled TX time like in the case of the tc-taprio and
tc-etf qdiscs.
EXAMPLES
To obtain the summary of the built-in metrics:
isochron report \
--input-file isochron.dat \
--summary
To see the detailed network timestamps for a single packet:
isochron report \
--input-file isochron.dat \
--printf-format "seqid %u scheduled for %T, TX qdisc %T sw %T hw %T, RX hw %T sw %T\n" \
--printf-args "qSstTRr" \
--start 173972 --stop 173972
To export data in comma-separated value format, for calculating user-defined metrics externally:
isochron report \
--input-file isochron.dat \
--printf-format "%d,%d\n" \
--printf-args "TR" \
> isochron.csv
User-defined arithmetic on the built-in isochron variables can also be delegated to a scripting language
interpreter such as Python, by configuring the isochron printf format specifier to generate output in
Python syntax:
isochron report \
--printf-format "pdelay=%d - %d\nprint(\"path_delay[%u] =\", pdelay)\n" \
--printf-args "RTq" \
| python3 -
For more complex arithmetic, the per-packet internal variables can be stored inside arrays:
printf "wakeup_latency = {}\n" > isochron_data.py
isochron report \
--printf-format "wakeup_latency[%u] = %d - (%d - %d)\n" \
--printf-args "qwSA" \
>> isochron_data.py
cat << 'EOF' > isochron_postprocess.py
#!/usr/bin/env python3
from isochron_data import wakeup_latency
import numpy as np
w = np.array(list(wakeup_latency.values()))
print("Wakeup latency: min {}, max {}, mean {}, median {}, stdev {}".format(np.min(w), np.max(w), np.mean(w), np.median(w), np.std(w)))
EOF
python3 ./isochron_postprocess.py
AUTHOR
isochron was written by Vladimir Oltean vladimir.oltean@nxp.com
SEE ALSO
isochron(8) isochron-send(8) isochron-rcv(8)
COMMENTS
This man page was written using pandoc by the same author.
isochron-report(1)