isochron-report - Gather statistics from logged isochron data
isochron report [OPTIONS]
This command opens an isochron.dat file generated by
isochron send and filters the requested data from
it.
- -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.
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).
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.
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.
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
This man page was written using
pandoc by the same
author.