rtla-hwnoise.rst

  1.. SPDX-License-Identifier: GPL-2.0
  2
  3.. |tool| replace:: hwnoise
  4
  5============
  6rtla-hwnoise
  7============
  8------------------------------------------
  9Detect and quantify hardware-related noise
 10------------------------------------------
 11
 12:Manual section: 1
 13
 14SYNOPSIS
 15========
 16
 17**rtla hwnoise** [*OPTIONS*]
 18
 19DESCRIPTION
 20===========
 21
 22**rtla hwnoise** collects the periodic summary from the *osnoise* tracer
 23running with *interrupts disabled*. By disabling interrupts, and the scheduling
 24of threads as a consequence, only non-maskable interrupts and hardware-related
 25noise is allowed.
 26
 27The tool also allows the configurations of the *osnoise* tracer and the
 28collection of the tracer output.
 29
 30OPTIONS
 31=======
 32.. include:: common_osnoise_options.txt
 33
 34.. include:: common_top_options.txt
 35
 36.. include:: common_options.txt
 37
 38EXAMPLE
 39=======
 40In the example below, the **rtla hwnoise** tool is set to run on CPUs *1-7*
 41on a system with 8 cores/16 threads with hyper-threading enabled.
 42
 43The tool is set to detect any noise higher than *one microsecond*,
 44to run for *ten minutes*, displaying a summary of the report at the
 45end of the session::
 46
 47  # rtla hwnoise -c 1-7 -T 1 -d 10m -q
 48                                          Hardware-related Noise
 49  duration:   0 00:10:00 | time is in us
 50  CPU Period       Runtime        Noise  % CPU Aval   Max Noise   Max Single          HW          NMI
 51    1 #599       599000000          138    99.99997           3            3           4           74
 52    2 #599       599000000           85    99.99998           3            3           4           75
 53    3 #599       599000000           86    99.99998           4            3           6           75
 54    4 #599       599000000           81    99.99998           4            4           2           75
 55    5 #599       599000000           85    99.99998           2            2           2           75
 56    6 #599       599000000           76    99.99998           2            2           0           75
 57    7 #599       599000000           77    99.99998           3            3           0           75
 58
 59
 60The first column shows the *CPU*, and the second column shows how many
 61*Periods* the tool ran during the session. The *Runtime* is the time
 62the tool effectively runs on the CPU. The *Noise* column is the sum of
 63all noise that the tool observed, and the *% CPU Aval* is the relation
 64between the *Runtime* and *Noise*.
 65
 66The *Max Noise* column is the maximum hardware noise the tool detected in a
 67single period, and the *Max Single* is the maximum single noise seen.
 68
 69The *HW* and *NMI* columns show the total number of *hardware* and *NMI* noise
 70occurrence observed by the tool.
 71
 72For example, *CPU 3* ran *599* periods of *1 second Runtime*. The CPU received
 73*86 us* of noise during the entire execution, leaving *99.99997 %* of CPU time
 74for the application. In the worst single period, the CPU caused *4 us* of
 75noise to the application, but it was certainly caused by more than one single
 76noise, as the *Max Single* noise was of *3 us*. The CPU has *HW noise,* at a
 77rate of *six occurrences*/*ten minutes*. The CPU also has *NMIs*, at a higher
 78frequency: around *seven per second*.
 79
 80The tool should report *0* hardware-related noise in the ideal situation.
 81For example, by disabling hyper-threading to remove the hardware noise,
 82and disabling the TSC watchdog to remove the NMI (it is possible to identify
 83this using tracing options of **rtla hwnoise**), it was possible to reach
 84the ideal situation in the same hardware::
 85
 86  # rtla hwnoise -c 1-7 -T 1 -d 10m -q
 87                                          Hardware-related Noise
 88  duration:   0 00:10:00 | time is in us
 89  CPU Period       Runtime        Noise  % CPU Aval   Max Noise   Max Single          HW          NMI
 90    1 #599       599000000            0   100.00000           0            0           0            0
 91    2 #599       599000000            0   100.00000           0            0           0            0
 92    3 #599       599000000            0   100.00000           0            0           0            0
 93    4 #599       599000000            0   100.00000           0            0           0            0
 94    5 #599       599000000            0   100.00000           0            0           0            0
 95    6 #599       599000000            0   100.00000           0            0           0            0
 96    7 #599       599000000            0   100.00000           0            0           0            0
 97
 98SEE ALSO
 99========
100
101**rtla-osnoise**\(1)
102
103Osnoise tracer documentation: <https://www.kernel.org/doc/html/latest/trace/osnoise-tracer.html>
104
105AUTHOR
106======
107Written by Daniel Bristot de Oliveira <bristot@kernel.org>
108
109.. include:: common_appendix.txt