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diff --git a/Documentation/tools/rtla/rtla-hwnoise.rst b/Documentation/tools/rtla/rtla-hwnoise.rst new file mode 100644 index 000000000000..fb1c52bbc00b --- /dev/null +++ b/Documentation/tools/rtla/rtla-hwnoise.rst @@ -0,0 +1,107 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============ +rtla-hwnoise +============ +------------------------------------------ +Detect and quantify hardware-related noise +------------------------------------------ + +: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 |