linux-kernel - [PATCH V2 6/6] Documentation/osnoise: Add osnoise/options documentation

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Message-Id: <f1a1569c22aef2744e0b787cdd414465750dc7c2.1669115208.git.bristot@kernel.org>
Date:   Wed, 23 Nov 2022 18:06:24 +0100
From:   Daniel Bristot de Oliveira <bristot@...nel.org>
To:     Daniel Bristot de Oliveira <bristot@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Juri Lelli <juri.lelli@...hat.com>,
        Clark Williams <williams@...hat.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH V2 6/6] Documentation/osnoise: Add osnoise/options documentation

Add the documentation about the osnoise/options file, the options,
and some additional explanation about the OSNOISE_WORKLOAD option.

Cc: Daniel Bristot de Oliveira <bristot@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Jonathan Corbet <corbet@....net>
Signed-off-by: Daniel Bristot de Oliveira <bristot@...nel.org>
---
 Documentation/trace/osnoise-tracer.rst | 32 ++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/Documentation/trace/osnoise-tracer.rst b/Documentation/trace/osnoise-tracer.rst
index 963def9f97c6..618bcdc90bb6 100644
--- a/Documentation/trace/osnoise-tracer.rst
+++ b/Documentation/trace/osnoise-tracer.rst
@@ -92,8 +92,8 @@ Note that the example above shows a high number of HW noise samples.
 The reason being is that this sample was taken on a virtual machine,
 and the host interference is detected as a hardware interference.
 
-Tracer options
----------------------
+Tracer Configuration
+--------------------
 
 The tracer has a set of options inside the osnoise directory, they are:
 
@@ -109,6 +109,27 @@ The tracer has a set of options inside the osnoise directory, they are:
  - tracing_threshold: the minimum delta between two time() reads to be
    considered as noise, in us. When set to 0, the default value will
    be used, which is currently 5 us.
+ - osnoise/options: a set of on/off options that can be enabled by
+   writing the option name to the file or disabled by writing the option
+   name preceded with the 'NO_' prefix. For example, writing
+   NO_OSNOISE_WORKLOAD disables the OSNOISE_WORKLOAD option. The
+   special DEAFAULTS option resets all options to the default value.
+
+Tracer Options
+--------------
+
+The osnoise/options file exposes a set of on/off configuration options for
+the osnoise tracer. These options are:
+
+ - DEFAULTS: reset the options to the default value.
+ - OSNOISE_WORKLOAD: do not dispatch osnoise workload (see dedicated
+   section below).
+ - PANIC_ON_STOP: call panic() if the tracer stops. This option serves to
+    capture a vmcore.
+ - OSNOISE_PREEMPT_DISABLE: disable preemption while running the osnoise
+   workload, allowing only IRQ-related and hardware-related noise.
+ - OSNOISE_IRQ_DISABLE: disable IRQs while running the osnoise workload,
+   allowing only NMIs and hardware-related noise, like hwlat tracer.
 
 Additional Tracing
 ------------------
@@ -150,3 +171,10 @@ tracepoints is smaller than eight us reported in the sample_threshold.
 The reason roots in the overhead of the entry and exit code that happens
 before and after any interference execution. This justifies the dual
 approach: measuring thread and tracing.
+
+Running osnoise tracer without workload
+---------------------------------------
+
+By enabling the osnoise tracer with the NO_OSNOISE_WORKLOAD option set,
+the osnoise: tracepoints serves to measure the execution time of
+any type of Linux task, free from the interference of other tasks.
-- 
2.32.0