[PATCH V2 0/6] Add osnoise/options file

[PATCH V2 0/6] Add osnoise/options file

[Daniel Bristot de Oliveira]

Was: Allow osnoise tracer to run without workload [1]

After adding the osnoise/options file, a set of on/off options
came to my mind, most based on discussions while debugging problems
with Juri and Clark.

So, this series now goes beyond running osnoise without a workload
by adding a set of practical options using the new osnoise/options file.

The [NO_]OSNOISE_WORKLOAD option allows the tracer to be dispatched
without workload, making the osnoise: tracepoints to become
generic events to measure the execution time of *any* task on Linux.

The PANIC_ON_STOP option facilitates the vmcore generation to aid
in the latency analysis using a crash dump.

The OSNOISE_PREEMPT_DISABLE and OSNOISE_IRQ_DISABLE options refine
the type of noise that the osnoise tracer detects, allowing the
tool to measure only IRQ-related noise, or NMI/HW-related noise,
respectively.

Each patch has a description of the options and the last patch
documents them in the osnoise documentation file.

[1] https://lore.kernel.org/r/cover.1668692096.git.bristot@kernel.org/

Changes from v1:
  - Changed the cover letter topic
  - Add Acked-by Masami to the first patch
  - Add the PANIC_ON_STOP option
  - Add the OSNOISE_PREEMPT_DISABLE and OSNOISE_IRQ_DISABLE options
  - Improved the documentationa

Daniel Bristot de Oliveira (6):
  tracing/osnoise: Fix duration type
  tracing/osnoise: Add osnoise/options file
  tracing/osnoise: Add OSNOISE_WORKLOAD option
  tracing/osnoise: Add PANIC_ON_STOP option
  tracing/osnoise: Add preempt and/or irq disabled options
  Documentation/osnoise: Add osnoise/options documentation

 Documentation/trace/osnoise-tracer.rst |  32 +++-
 kernel/trace/trace_osnoise.c           | 242 +++++++++++++++++++++++--
 2 files changed, 261 insertions(+), 13 deletions(-)

-- 
2.32.0

[PATCH V2 1/6] tracing/osnoise: Fix duration type

[Daniel Bristot de Oliveira]

The duration type is a 64 long value, not an int. This was
causing some long noise to report wrong values.

Change the duration to a 64 bits value.

Fixes: bce29ac9ce0b ("trace: Add osnoise tracer")
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
---
 kernel/trace/trace_osnoise.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 78d536d3ff3d..4300c5dc4e5d 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -917,7 +917,7 @@ void osnoise_trace_irq_entry(int id)
 void osnoise_trace_irq_exit(int id, const char *desc)
 {
 	struct osnoise_variables *osn_var = this_cpu_osn_var();
-	int duration;
+	s64 duration;
 
 	if (!osn_var->sampling)
 		return;
@@ -1048,7 +1048,7 @@ static void trace_softirq_entry_callback(void *data, unsigned int vec_nr)
 static void trace_softirq_exit_callback(void *data, unsigned int vec_nr)
 {
 	struct osnoise_variables *osn_var = this_cpu_osn_var();
-	int duration;
+	s64 duration;
 
 	if (!osn_var->sampling)
 		return;
@@ -1144,7 +1144,7 @@ thread_entry(struct osnoise_variables *osn_var, struct task_struct *t)
 static void
 thread_exit(struct osnoise_variables *osn_var, struct task_struct *t)
 {
-	int duration;
+	s64 duration;
 
 	if (!osn_var->sampling)
 		return;
-- 
2.32.0

[PATCH V2 2/6] tracing/osnoise: Add osnoise/options file

[Daniel Bristot de Oliveira]

Add the tracing/osnoise/options file to control osnoise/timerlat
tracer features. It is a single file to contain multiple features,
similar to the sched/features file.

Reading the file displays a list of options. Writing the OPTION_NAME
enables it, writing NO_OPTION_NAME disables it.

The DEAFULTS is a particular option that resets the options to the
default ones.

It uses a bitmask to keep track of the status of the option. When needed,
we can add a list of static keys, but for now it does not justify the
memory increase.

Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
---
 kernel/trace/trace_osnoise.c | 170 +++++++++++++++++++++++++++++++++++
 1 file changed, 170 insertions(+)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 4300c5dc4e5d..17b77fe3950b 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -48,6 +48,19 @@
 #define DEFAULT_TIMERLAT_PERIOD	1000			/* 1ms */
 #define DEFAULT_TIMERLAT_PRIO	95			/* FIFO 95 */
 
+/*
+ * osnoise/options entries.
+ */
+enum osnoise_options_index {
+	OSN_DEFAULTS = 0,
+	OSN_MAX
+};
+
+static const char * const osnoise_options_str[OSN_MAX] = { "DEFAULTS" };
+
+#define OSN_DEFAULT_OPTIONS	0
+unsigned long osnoise_options	= OSN_DEFAULT_OPTIONS;
+
 /*
  * trace_array of the enabled osnoise/timerlat instances.
  */
@@ -1860,6 +1873,150 @@ static void osnoise_init_hotplug_support(void)
 }
 #endif /* CONFIG_HOTPLUG_CPU */
 
+/*
+ * seq file functions for the osnoise/options file.
+ */
+static void *s_options_start(struct seq_file *s, loff_t *pos)
+{
+	int option = *pos;
+
+	mutex_lock(&interface_lock);
+
+	if (option >= OSN_MAX)
+		return NULL;
+
+	return pos;
+}
+
+static void *s_options_next(struct seq_file *s, void *v, loff_t *pos)
+{
+	int option = ++(*pos);
+
+	if (option >= OSN_MAX)
+		return NULL;
+
+	return pos;
+}
+
+static int s_options_show(struct seq_file *s, void *v)
+{
+	loff_t *pos = v;
+	int option = *pos;
+
+	if (option == OSN_DEFAULTS) {
+		if (osnoise_options == OSN_DEFAULT_OPTIONS)
+			seq_printf(s, "%s", osnoise_options_str[option]);
+		else
+			seq_printf(s, "NO_%s", osnoise_options_str[option]);
+		goto out;
+	}
+
+	if (test_bit(option, &osnoise_options))
+		seq_printf(s, "%s", osnoise_options_str[option]);
+	else
+		seq_printf(s, "NO_%s", osnoise_options_str[option]);
+
+out:
+	if (option != OSN_MAX)
+		seq_puts(s, " ");
+
+	return 0;
+}
+
+static void s_options_stop(struct seq_file *s, void *v)
+{
+	seq_puts(s, "\n");
+	mutex_unlock(&interface_lock);
+}
+
+static const struct seq_operations osnoise_options_seq_ops = {
+	.start		= s_options_start,
+	.next		= s_options_next,
+	.show		= s_options_show,
+	.stop		= s_options_stop
+};
+
+static int osnoise_options_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &osnoise_options_seq_ops);
+};
+
+/**
+ * osnoise_options_write - Write function for "options" entry
+ * @filp: The active open file structure
+ * @ubuf: The user buffer that contains the value to write
+ * @cnt: The maximum number of bytes to write to "file"
+ * @ppos: The current position in @file
+ *
+ * Writing the option name sets the option, writing the "NO_"
+ * prefix in front of the option name disables it.
+ *
+ * Writing "DEFAULTS" resets the option values to the default ones.
+ */
+static ssize_t osnoise_options_write(struct file *filp, const char __user *ubuf,
+				     size_t cnt, loff_t *ppos)
+{
+	int running, option, enable, retval;
+	char buf[256], *option_str;
+
+	if (cnt >= 256)
+		return -EINVAL;
+
+	if (copy_from_user(buf, ubuf, cnt))
+		return -EFAULT;
+
+	buf[cnt] = 0;
+
+	if (strncmp(buf, "NO_", 3)) {
+		option_str = strstrip(buf);
+		enable = true;
+	} else {
+		option_str = strstrip(&buf[3]);
+		enable = false;
+	}
+
+	option = match_string(osnoise_options_str, OSN_MAX, option_str);
+	if (option < 0)
+		return -EINVAL;
+
+	/*
+	 * trace_types_lock is taken to avoid concurrency on start/stop.
+	 */
+	mutex_lock(&trace_types_lock);
+	running = osnoise_has_registered_instances();
+	if (running)
+		stop_per_cpu_kthreads();
+
+	mutex_lock(&interface_lock);
+	/*
+	 * avoid CPU hotplug operations that might read options.
+	 */
+	cpus_read_lock();
+
+	retval = cnt;
+
+	if (enable) {
+		if (option == OSN_DEFAULTS)
+			osnoise_options = OSN_DEFAULT_OPTIONS;
+		else
+			set_bit(option, &osnoise_options);
+	} else {
+		if (option == OSN_DEFAULTS)
+			retval = -EINVAL;
+		else
+			clear_bit(option, &osnoise_options);
+	}
+
+	cpus_read_unlock();
+	mutex_unlock(&interface_lock);
+
+	if (running)
+		start_per_cpu_kthreads();
+	mutex_unlock(&trace_types_lock);
+
+	return retval;
+}
+
 /*
  * osnoise_cpus_read - Read function for reading the "cpus" file
  * @filp: The active open file structure
@@ -2042,6 +2199,14 @@ static const struct file_operations cpus_fops = {
 	.llseek		= generic_file_llseek,
 };
 
+static const struct file_operations osnoise_options_fops = {
+	.open		= osnoise_options_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+	.write		= osnoise_options_write
+};
+
 #ifdef CONFIG_TIMERLAT_TRACER
 #ifdef CONFIG_STACKTRACE
 static int init_timerlat_stack_tracefs(struct dentry *top_dir)
@@ -2128,6 +2293,11 @@ static int init_tracefs(void)
 	if (!tmp)
 		goto err;
 
+	tmp = trace_create_file("options", TRACE_MODE_WRITE, top_dir, NULL,
+				&osnoise_options_fops);
+	if (!tmp)
+		goto err;
+
 	ret = init_timerlat_tracefs(top_dir);
 	if (ret)
 		goto err;
-- 
2.32.0

[PATCH V2 3/6] tracing/osnoise: Add OSNOISE_WORKLOAD option

[Daniel Bristot de Oliveira]

The osnoise tracer is not only a tracer, and a set of tracepoints,
but also a workload dispatcher.

In preparation for having other workloads, e.g., in user-space,
add an option to avoid dispatching the workload.

By not dispatching the workload, the osnoise: tracepoints become
generic events to measure the execution time of *any* task on Linux.

For example:

  # cd /sys/kernel/tracing/
  # cat osnoise/options
  DEFAULTS OSNOISE_WORKLOAD
  # echo NO_OSNOISE_WORKLOAD > osnoise/options
  # cat osnoise/options
  NO_DEFAULTS NO_OSNOISE_WORKLOAD
  # echo osnoise > set_event
  # echo osnoise > current_tracer
  # tail -8 trace
      make-94722   [002] d..3.  1371.794507: thread_noise:     make:94722 start 1371.794302286 duration 200897 ns
        sh-121042  [020] d..3.  1371.794534: thread_noise:       sh:121042 start 1371.781610976 duration 8943683 ns
      make-121097  [005] d..3.  1371.794542: thread_noise:     make:121097 start 1371.794481522 duration 60444 ns
     <...>-40      [005] d..3.  1371.794550: thread_noise: migration/5:40 start 1371.794542256 duration 7154 ns
    <idle>-0       [018] dNh2.  1371.794554: irq_noise: reschedule:253 start 1371.794553547 duration 40 ns
    <idle>-0       [018] dNh2.  1371.794561: irq_noise: local_timer:236 start 1371.794556222 duration 4890 ns
    <idle>-0       [018] .Ns2.  1371.794563: softirq_noise:    SCHED:7 start 1371.794561803 duration 992 ns
    <idle>-0       [018] d..3.  1371.794566: thread_noise: swapper/18:0 start 1371.781368110 duration 13191798 ns

In preparation for the rtla exec_time tracer/tool and
rtla osnoise --user option.

Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
---
 kernel/trace/trace_osnoise.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 17b77fe3950b..3f10dd1f2f1c 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -53,12 +53,13 @@
  */
 enum osnoise_options_index {
 	OSN_DEFAULTS = 0,
+	OSN_WORKLOAD,
 	OSN_MAX
 };
 
-static const char * const osnoise_options_str[OSN_MAX] = { "DEFAULTS" };
+static const char * const osnoise_options_str[OSN_MAX] = { "DEFAULTS", "OSNOISE_WORKLOAD" };
 
-#define OSN_DEFAULT_OPTIONS	0
+#define OSN_DEFAULT_OPTIONS	0x2
 unsigned long osnoise_options	= OSN_DEFAULT_OPTIONS;
 
 /*
@@ -1186,11 +1187,12 @@ trace_sched_switch_callback(void *data, bool preempt,
 			    unsigned int prev_state)
 {
 	struct osnoise_variables *osn_var = this_cpu_osn_var();
+	int workload = test_bit(OSN_WORKLOAD, &osnoise_options);
 
-	if (p->pid != osn_var->pid)
+	if ((p->pid != osn_var->pid) || !workload)
 		thread_exit(osn_var, p);
 
-	if (n->pid != osn_var->pid)
+	if ((n->pid != osn_var->pid) || !workload)
 		thread_entry(osn_var, n);
 }
 
@@ -1723,9 +1725,16 @@ static void stop_kthread(unsigned int cpu)
 	struct task_struct *kthread;
 
 	kthread = per_cpu(per_cpu_osnoise_var, cpu).kthread;
-	if (kthread)
+	if (kthread) {
 		kthread_stop(kthread);
-	per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;
+		per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;
+	} else {
+		if (!test_bit(OSN_WORKLOAD, &osnoise_options)) {
+			per_cpu(per_cpu_osnoise_var, cpu).sampling = false;
+			barrier();
+			return;
+		}
+	}
 }
 
 /*
@@ -1759,6 +1768,13 @@ static int start_kthread(unsigned int cpu)
 		snprintf(comm, 24, "timerlat/%d", cpu);
 		main = timerlat_main;
 	} else {
+		/* if no workload, just return */
+		if (!test_bit(OSN_WORKLOAD, &osnoise_options)) {
+			per_cpu(per_cpu_osnoise_var, cpu).sampling = true;
+			barrier();
+			return 0;
+		}
+
 		snprintf(comm, 24, "osnoise/%d", cpu);
 	}
 
-- 
2.32.0

[PATCH V2 4/6] tracing/osnoise: Add PANIC_ON_STOP option

[Daniel Bristot de Oliveira]

Often the latency observed in a CPU is not caused by the work being done
in the CPU itself, but by work done on another CPU that causes the
hardware to stall all CPUs. In this case, it is interesting to know
what is happening on ALL CPUs, and the best way to do this is via
crash dump analysis.

Add the PANIC_ON_STOP option to osnoise/timerlat tracers. The default
behavior is having this option off. When enabled by the user, the system
will panic after hitting a stop tracing condition.

This option was motivated by a real scenario that Juri Lelli and I
were debugging.

Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
---
 kernel/trace/trace_osnoise.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 3f10dd1f2f1c..801eba0b5cf8 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -54,10 +54,11 @@
 enum osnoise_options_index {
 	OSN_DEFAULTS = 0,
 	OSN_WORKLOAD,
+	OSN_PANIC_ON_STOP,
 	OSN_MAX
 };
 
-static const char * const osnoise_options_str[OSN_MAX] = { "DEFAULTS", "OSNOISE_WORKLOAD" };
+static const char * const osnoise_options_str[OSN_MAX] = { "DEFAULTS", "OSNOISE_WORKLOAD", "PANIC_ON_STOP" };
 
 #define OSN_DEFAULT_OPTIONS	0x2
 unsigned long osnoise_options	= OSN_DEFAULT_OPTIONS;
@@ -1270,6 +1271,9 @@ static __always_inline void osnoise_stop_tracing(void)
 		trace_array_printk_buf(tr->array_buffer.buffer, _THIS_IP_,
 				"stop tracing hit on cpu %d\n", smp_processor_id());
 
+		if (test_bit(OSN_PANIC_ON_STOP, &osnoise_options))
+			panic("tracer hit stop condition on CPU %d\n", smp_processor_id());
+
 		tracer_tracing_off(tr);
 	}
 	rcu_read_unlock();
-- 
2.32.0

[PATCH V2 5/6] tracing/osnoise: Add preempt and/or irq disabled options

[Daniel Bristot de Oliveira]

The osnoise workload runs with preemption and IRQs enabled in such
a way as to allow all sorts of noise to disturb osnoise's execution.
hwlat tracer has a similar workload but works with irq disabled,
allowing only NMIs and the hardware to generate noise.

While thinking about adding an options file to hwlat tracer to
allow the system to panic, and other features I was thinking
to add, like having a tracepoint at each noise detection, it
came to my mind that is easier to make osnoise and also do
hardware latency detection than making hwlat "feature compatible"
with osnoise.

Other points are:
 - osnoise already has an independent cpu file.
 - osnoise has a more intuitive interface, e.g., runtime/period vs.
   window/width (and people often need help remembering what it is).
 - osnoise: tracepoints
 - osnoise stop options
 - osnoise options file itself

Moreover, the user-space side (in rtla) is simplified by reusing the
existing osnoise code.

Finally, people have been asking me about using osnoise for hw latency
detection, and I have to explain that it was sufficient but not
necessary. These options make it sufficient and necessary.

Adding a Suggested-by Clark, as he often asked me about this
possibility.

Cc: Suggested-by: Clark Williams <williams@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
---
 kernel/trace/trace_osnoise.c | 40 +++++++++++++++++++++++++++++++-----
 1 file changed, 35 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 801eba0b5cf8..14b7f4092982 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -55,10 +55,17 @@ enum osnoise_options_index {
 	OSN_DEFAULTS = 0,
 	OSN_WORKLOAD,
 	OSN_PANIC_ON_STOP,
+	OSN_PREEMPT_DISABLE,
+	OSN_IRQ_DISABLE,
 	OSN_MAX
 };
 
-static const char * const osnoise_options_str[OSN_MAX] = { "DEFAULTS", "OSNOISE_WORKLOAD", "PANIC_ON_STOP" };
+static const char * const osnoise_options_str[OSN_MAX] = {
+							"DEFAULTS",
+							"OSNOISE_WORKLOAD",
+							"PANIC_ON_STOP",
+							"OSNOISE_PREEMPT_DISABLE",
+							"OSNOISE_IRQ_DISABLE" };
 
 #define OSN_DEFAULT_OPTIONS	0x2
 unsigned long osnoise_options	= OSN_DEFAULT_OPTIONS;
@@ -1308,6 +1315,8 @@ static void notify_new_max_latency(u64 latency)
  */
 static int run_osnoise(void)
 {
+	bool preempt_disable = test_bit(OSN_PREEMPT_DISABLE, &osnoise_options);
+	bool irq_disable = test_bit(OSN_IRQ_DISABLE, &osnoise_options);
 	struct osnoise_variables *osn_var = this_cpu_osn_var();
 	u64 start, sample, last_sample;
 	u64 last_int_count, int_count;
@@ -1335,6 +1344,14 @@ static int run_osnoise(void)
 	 */
 	threshold = tracing_thresh ? : 5000;
 
+	/*
+	 * IRQ disable also implies in preempt disable.
+	 */
+	if (irq_disable)
+		local_irq_disable();
+	else if (preempt_disable)
+		preempt_disable();
+
 	/*
 	 * Make sure NMIs see sampling first
 	 */
@@ -1422,16 +1439,21 @@ static int run_osnoise(void)
 		 * cond_resched()
 		 */
 		if (IS_ENABLED(CONFIG_PREEMPT_RCU)) {
-			local_irq_disable();
+			if (!irq_disable)
+				local_irq_disable();
+
 			rcu_momentary_dyntick_idle();
-			local_irq_enable();
+
+			if (!irq_disable)
+				local_irq_enable();
 		}
 
 		/*
 		 * For the non-preemptive kernel config: let threads runs, if
-		 * they so wish.
+		 * they so wish, unless set not do to so.
 		 */
-		cond_resched();
+		if (!irq_disable && !preempt_disable)
+			cond_resched();
 
 		last_sample = sample;
 		last_int_count = int_count;
@@ -1450,6 +1472,14 @@ static int run_osnoise(void)
 	 */
 	barrier();
 
+	/*
+	 * Return to the preemptive state.
+	 */
+	if (irq_disable)
+		local_irq_enable();
+	else if (preempt_disable)
+		preempt_enable();
+
 	/*
 	 * Save noise info.
 	 */
-- 
2.32.0

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

[Daniel Bristot de Oliveira]

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@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.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