.. SPDX-License-Identifier: GPL-2.0
============
rtla-hwnoise
============
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Detect and quantify hardware-related noise
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:Manual section: 1
SYNOPSIS
========
**rtla hwnoise** [*OPTIONS*]
DESCRIPTION
===========
**rtla hwnoise** collects the periodic summary from the *osnoise* tracer
running with *interrupts disabled*. By disabling interrupts, and the scheduling
of threads as a consequence, only non-maskable interrupts and hardware-related
noise is allowed.
The tool also allows the configurations of the *osnoise* tracer and the
collection of the tracer output.
OPTIONS
=======
.. include:: common_osnoise_options.rst
.. include:: common_top_options.rst
.. include:: common_options.rst
EXAMPLE
=======
In the example below, the **rtla hwnoise** tool is set to run on CPUs *1-7*
on a system with 8 cores/16 threads with hyper-threading enabled.
The tool is set to detect any noise higher than *one microsecond*,
to run for *ten minutes*, displaying a summary of the report at the
end of the session::
# rtla hwnoise -c 1-7 -T 1 -d 10m -q
Hardware-related Noise
duration: 0 00:10:00 | time is in us
CPU Period Runtime Noise % CPU Aval Max Noise Max Single HW NMI
1 #599 599000000 138 99.99997 3 3 4 74
2 #599 599000000 85 99.99998 3 3 4 75
3 #599 599000000 86 99.99998 4 3 6 75
4 #599 599000000 81 99.99998 4 4 2 75
5 #599 599000000 85 99.99998 2 2 2 75
6 #599 599000000 76 99.99998 2 2 0 75
7 #599 599000000 77 99.99998 3 3 0 75
The first column shows the *CPU*, and the second column shows how many
*Periods* the tool ran during the session. The *Runtime* is the time
the tool effectively runs on the CPU. The *Noise* column is the sum of
all noise that the tool observed, and the *% CPU Aval* is the relation
between the *Runtime* and *Noise*.
The *Max Noise* column is the maximum hardware noise the tool detected in a
single period, and the *Max Single* is the maximum single noise seen.
The *HW* and *NMI* columns show the total number of *hardware* and *NMI* noise
occurrence observed by the tool.
For example, *CPU 3* ran *599* periods of *1 second Runtime*. The CPU received
*86 us* of noise during the entire execution, leaving *99.99997 %* of CPU time
for the application. In the worst single period, the CPU caused *4 us* of
noise to the application, but it was certainly caused by more than one single
noise, as the *Max Single* noise was of *3 us*. The CPU has *HW noise,* at a
rate of *six occurrences*/*ten minutes*. The CPU also has *NMIs*, at a higher
frequency: around *seven per second*.
The tool should report *0* hardware-related noise in the ideal situation.
For example, by disabling hyper-threading to remove the hardware noise,
and disabling the TSC watchdog to remove the NMI (it is possible to identify
this using tracing options of **rtla hwnoise**), it was possible to reach
the ideal situation in the same hardware::
# rtla hwnoise -c 1-7 -T 1 -d 10m -q
Hardware-related Noise
duration: 0 00:10:00 | time is in us
CPU Period Runtime Noise % CPU Aval Max Noise Max Single HW NMI
1 #599 599000000 0 100.00000 0 0 0 0
2 #599 599000000 0 100.00000 0 0 0 0
3 #599 599000000 0 100.00000 0 0 0 0
4 #599 599000000 0 100.00000 0 0 0 0
5 #599 599000000 0 100.00000 0 0 0 0
6 #599 599000000 0 100.00000 0 0 0 0
7 #599 599000000 0 100.00000 0 0 0 0
SEE ALSO
========
**rtla-osnoise**\(1)
Osnoise tracer documentation: <https://www.kernel.org/doc/html/latest/trace/osnoise-tracer.html>
AUTHOR
======
Written by Daniel Bristot de Oliveira <bristot@kernel.org>
.. include:: common_appendix.rst