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