[for-next][PATCH 11/24] trace/hwlat: Fix Clarks email

[for-next][PATCH 11/24] trace/hwlat: Fix Clarks email

[Steven Rostedt]

From: Daniel Bristot de Oliveira <bristot@redhat.com>

Clark's email is williams@redhat.com.

No functional change.

Link: https://lkml.kernel.org/r/6fa4b49e17ab8a1ff19c335ab7cde38d8afb0e29.1624372313.git.bristot@redhat.com

Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace_hwlat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index 632ef88131a9..0a5635401125 100644
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -34,7 +34,7 @@
  * Copyright (C) 2008-2009 Jon Masters, Red Hat, Inc. <jcm@redhat.com>
  * Copyright (C) 2013-2016 Steven Rostedt, Red Hat, Inc. <srostedt@redhat.com>
  *
- * Includes useful feedback from Clark Williams <clark@redhat.com>
+ * Includes useful feedback from Clark Williams <williams@redhat.com>
  *
  */
 #include <linux/kthread.h>
-- 
2.30.2

[for-next][PATCH 12/24] trace/hwlat: Implement the mode config option

[Steven Rostedt]

From: Daniel Bristot de Oliveira <bristot@redhat.com>

Provides the "mode" config to the hardware latency detector. hwlatd has
two different operation modes. The default mode is the "round-robin" one,
in which a single hwlatd thread runs, migrating among the allowed CPUs in a
"round-robin" fashion. This is the current behavior.

The "none" sets the allowed cpumask for a single hwlatd thread at the
startup, but skips the round-robin, letting the scheduler handle the
migration.

In preparation to the per-cpu mode.

Link: https://lkml.kernel.org/r/f3b1271262aa030c680e26615c1b9b2d71e55e92.1624372313.git.bristot@redhat.com

Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 Documentation/trace/hwlat_detector.rst |  12 +-
 kernel/trace/trace_hwlat.c             | 179 +++++++++++++++++++++++--
 2 files changed, 175 insertions(+), 16 deletions(-)

diff --git a/Documentation/trace/hwlat_detector.rst b/Documentation/trace/hwlat_detector.rst
index 5739349649c8..4d952df0586a 100644
--- a/Documentation/trace/hwlat_detector.rst
+++ b/Documentation/trace/hwlat_detector.rst
@@ -76,8 +76,12 @@ in /sys/kernel/tracing:
  - tracing_cpumask	- the CPUs to move the hwlat thread across
  - hwlat_detector/width	- specified amount of time to spin within window (usecs)
  - hwlat_detector/window	- amount of time between (width) runs (usecs)
+ - hwlat_detector/mode	- the thread mode
 
-The hwlat detector's kernel thread will migrate across each CPU specified in
-tracing_cpumask between each window. To limit the migration, either modify
-tracing_cpumask, or modify the hwlat kernel thread (named [hwlatd]) CPU
-affinity directly, and the migration will stop.
+By default, the hwlat detector's kernel thread will migrate across each CPU
+specified in cpumask at the beginning of a new window, in a round-robin
+fashion. This behavior can be changed by changing the thread mode,
+the available options are:
+
+ - none:        do not force migration
+ - round-robin: migrate across each CPU specified in cpumask [default]
diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index 0a5635401125..43a436d85a01 100644
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -59,6 +59,14 @@ static struct task_struct *hwlat_kthread;
 
 static struct dentry *hwlat_sample_width;	/* sample width us */
 static struct dentry *hwlat_sample_window;	/* sample window us */
+static struct dentry *hwlat_thread_mode;	/* hwlat thread mode */
+
+enum {
+	MODE_NONE = 0,
+	MODE_ROUND_ROBIN,
+	MODE_MAX
+};
+static char *thread_mode_str[] = { "none", "round-robin" };
 
 /* Save the previous tracing_thresh value */
 static unsigned long save_tracing_thresh;
@@ -96,11 +104,16 @@ static struct hwlat_data {
 	u64	sample_window;		/* total sampling window (on+off) */
 	u64	sample_width;		/* active sampling portion of window */
 
+	int	thread_mode;		/* thread mode */
+
 } hwlat_data = {
 	.sample_window		= DEFAULT_SAMPLE_WINDOW,
 	.sample_width		= DEFAULT_SAMPLE_WIDTH,
+	.thread_mode		= MODE_ROUND_ROBIN
 };
 
+static bool hwlat_busy;
+
 static void trace_hwlat_sample(struct hwlat_sample *sample)
 {
 	struct trace_array *tr = hwlat_trace;
@@ -328,7 +341,8 @@ static int kthread_fn(void *data)
 
 	while (!kthread_should_stop()) {
 
-		move_to_next_cpu();
+		if (hwlat_data.thread_mode == MODE_ROUND_ROBIN)
+			move_to_next_cpu();
 
 		local_irq_disable();
 		get_sample();
@@ -351,7 +365,7 @@ static int kthread_fn(void *data)
 	return 0;
 }
 
-/**
+/*
  * start_kthread - Kick off the hardware latency sampling/detector kthread
  *
  * This starts the kernel thread that will sit and sample the CPU timestamp
@@ -366,11 +380,6 @@ static int start_kthread(struct trace_array *tr)
 	if (hwlat_kthread)
 		return 0;
 
-	/* Just pick the first CPU on first iteration */
-	get_online_cpus();
-	cpumask_and(current_mask, cpu_online_mask, tr->tracing_cpumask);
-	put_online_cpus();
-	next_cpu = cpumask_first(current_mask);
 
 	kthread = kthread_create(kthread_fn, NULL, "hwlatd");
 	if (IS_ERR(kthread)) {
@@ -378,8 +387,19 @@ static int start_kthread(struct trace_array *tr)
 		return -ENOMEM;
 	}
 
-	cpumask_clear(current_mask);
-	cpumask_set_cpu(next_cpu, current_mask);
+
+	/* Just pick the first CPU on first iteration */
+	get_online_cpus();
+	cpumask_and(current_mask, cpu_online_mask, tr->tracing_cpumask);
+	put_online_cpus();
+
+	if (hwlat_data.thread_mode == MODE_ROUND_ROBIN) {
+		next_cpu = cpumask_first(current_mask);
+		cpumask_clear(current_mask);
+		cpumask_set_cpu(next_cpu, current_mask);
+
+	}
+
 	sched_setaffinity(kthread->pid, current_mask);
 
 	hwlat_kthread = kthread;
@@ -388,7 +408,7 @@ static int start_kthread(struct trace_array *tr)
 	return 0;
 }
 
-/**
+/*
  * stop_kthread - Inform the hardware latency sampling/detector kthread to stop
  *
  * This kicks the running hardware latency sampling/detector kernel thread and
@@ -511,6 +531,129 @@ hwlat_window_write(struct file *filp, const char __user *ubuf,
 	return cnt;
 }
 
+static void *s_mode_start(struct seq_file *s, loff_t *pos)
+{
+	int mode = *pos;
+
+	mutex_lock(&hwlat_data.lock);
+
+	if (mode >= MODE_MAX)
+		return NULL;
+
+	return pos;
+}
+
+static void *s_mode_next(struct seq_file *s, void *v, loff_t *pos)
+{
+	int mode = ++(*pos);
+
+	if (mode >= MODE_MAX)
+		return NULL;
+
+	return pos;
+}
+
+static int s_mode_show(struct seq_file *s, void *v)
+{
+	loff_t *pos = v;
+	int mode = *pos;
+
+	if (mode == hwlat_data.thread_mode)
+		seq_printf(s, "[%s]", thread_mode_str[mode]);
+	else
+		seq_printf(s, "%s", thread_mode_str[mode]);
+
+	if (mode != MODE_MAX)
+		seq_puts(s, " ");
+
+	return 0;
+}
+
+static void s_mode_stop(struct seq_file *s, void *v)
+{
+	seq_puts(s, "\n");
+	mutex_unlock(&hwlat_data.lock);
+}
+
+static const struct seq_operations thread_mode_seq_ops = {
+	.start		= s_mode_start,
+	.next		= s_mode_next,
+	.show		= s_mode_show,
+	.stop		= s_mode_stop
+};
+
+static int hwlat_mode_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &thread_mode_seq_ops);
+};
+
+static void hwlat_tracer_start(struct trace_array *tr);
+static void hwlat_tracer_stop(struct trace_array *tr);
+
+/**
+ * hwlat_mode_write - Write function for "mode" 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
+ *
+ * This function provides a write implementation for the "mode" interface
+ * to the hardware latency detector. hwlatd has different operation modes.
+ * The "none" sets the allowed cpumask for a single hwlatd thread at the
+ * startup and lets the scheduler handle the migration. The default mode is
+ * the "round-robin" one, in which a single hwlatd thread runs, migrating
+ * among the allowed CPUs in a round-robin fashion.
+ */
+static ssize_t hwlat_mode_write(struct file *filp, const char __user *ubuf,
+				 size_t cnt, loff_t *ppos)
+{
+	struct trace_array *tr = hwlat_trace;
+	const char *mode;
+	char buf[64];
+	int ret, i;
+
+	if (cnt >= sizeof(buf))
+		return -EINVAL;
+
+	if (copy_from_user(buf, ubuf, cnt))
+		return -EFAULT;
+
+	buf[cnt] = 0;
+
+	mode = strstrip(buf);
+
+	ret = -EINVAL;
+
+	/*
+	 * trace_types_lock is taken to avoid concurrency on start/stop
+	 * and hwlat_busy.
+	 */
+	mutex_lock(&trace_types_lock);
+	if (hwlat_busy)
+		hwlat_tracer_stop(tr);
+
+	mutex_lock(&hwlat_data.lock);
+
+	for (i = 0; i < MODE_MAX; i++) {
+		if (strcmp(mode, thread_mode_str[i]) == 0) {
+			hwlat_data.thread_mode = i;
+			ret = cnt;
+		}
+	}
+
+	mutex_unlock(&hwlat_data.lock);
+
+	if (hwlat_busy)
+		hwlat_tracer_start(tr);
+	mutex_unlock(&trace_types_lock);
+
+	*ppos += cnt;
+
+
+
+	return ret;
+}
+
 static const struct file_operations width_fops = {
 	.open		= tracing_open_generic,
 	.read		= hwlat_read,
@@ -523,6 +666,13 @@ static const struct file_operations window_fops = {
 	.write		= hwlat_window_write,
 };
 
+static const struct file_operations thread_mode_fops = {
+	.open		= hwlat_mode_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+	.write		= hwlat_mode_write
+};
 /**
  * init_tracefs - A function to initialize the tracefs interface files
  *
@@ -558,6 +708,13 @@ static int init_tracefs(void)
 	if (!hwlat_sample_width)
 		goto err;
 
+	hwlat_thread_mode = trace_create_file("mode", 0644,
+					      top_dir,
+					      NULL,
+					      &thread_mode_fops);
+	if (!hwlat_thread_mode)
+		goto err;
+
 	return 0;
 
  err:
@@ -579,8 +736,6 @@ static void hwlat_tracer_stop(struct trace_array *tr)
 	stop_kthread();
 }
 
-static bool hwlat_busy;
-
 static int hwlat_tracer_init(struct trace_array *tr)
 {
 	/* Only allow one instance to enable this */
-- 
2.30.2

[for-next][PATCH 13/24] trace/hwlat: Switch disable_migrate to mode none

[Steven Rostedt]

From: Daniel Bristot de Oliveira <bristot@redhat.com>

When in the round-robin mode, if the tracer detects a change in the
hwlatd thread affinity by an external tool, e.g., taskset, the
round-robin logic is disabled. The disable_migrate variable currently
tracks this.

With the addition of the "mode" config and the mode "none," the
disable_migrate logic is equivalent to switch to the "none" mode.

Hence, instead of using a hidden variable to track this behavior,
switch the mode to none, informing the user about this change.

Link: https://lkml.kernel.org/r/a679af672458d6b1f62252605905c5214030f247.1624372313.git.bristot@redhat.com

Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace_hwlat.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index 43a436d85a01..bae74b95cf55 100644
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -286,7 +286,6 @@ static int get_sample(void)
 }
 
 static struct cpumask save_cpumask;
-static bool disable_migrate;
 
 static void move_to_next_cpu(void)
 {
@@ -294,15 +293,13 @@ static void move_to_next_cpu(void)
 	struct trace_array *tr = hwlat_trace;
 	int next_cpu;
 
-	if (disable_migrate)
-		return;
 	/*
 	 * If for some reason the user modifies the CPU affinity
 	 * of this thread, then stop migrating for the duration
 	 * of the current test.
 	 */
 	if (!cpumask_equal(current_mask, current->cpus_ptr))
-		goto disable;
+		goto change_mode;
 
 	get_online_cpus();
 	cpumask_and(current_mask, cpu_online_mask, tr->tracing_cpumask);
@@ -313,7 +310,7 @@ static void move_to_next_cpu(void)
 		next_cpu = cpumask_first(current_mask);
 
 	if (next_cpu >= nr_cpu_ids) /* Shouldn't happen! */
-		goto disable;
+		goto change_mode;
 
 	cpumask_clear(current_mask);
 	cpumask_set_cpu(next_cpu, current_mask);
@@ -321,8 +318,9 @@ static void move_to_next_cpu(void)
 	sched_setaffinity(0, current_mask);
 	return;
 
- disable:
-	disable_migrate = true;
+ change_mode:
+	hwlat_data.thread_mode = MODE_NONE;
+	pr_info(BANNER "cpumask changed while in round-robin mode, switching to mode none\n");
 }
 
 /*
@@ -744,7 +742,6 @@ static int hwlat_tracer_init(struct trace_array *tr)
 
 	hwlat_trace = tr;
 
-	disable_migrate = false;
 	hwlat_data.count = 0;
 	tr->max_latency = 0;
 	save_tracing_thresh = tracing_thresh;
-- 
2.30.2

[for-next][PATCH 14/24] trace/hwlat: Implement the per-cpu mode

[Steven Rostedt]

From: Daniel Bristot de Oliveira <bristot@redhat.com>

Implements the per-cpu mode in which a sampling thread is created for
each cpu in the "cpus" (and tracing_mask).

The per-cpu mode has the potention to speed up the hwlat detection by
running on multiple CPUs at the same time, at the cost of higher cpu
usage with irqs disabled. Use with care.

[
  Changed get_cpu_data() to static.
  Reported-by: kernel test robot <lkp@intel.com>
]

Link: https://lkml.kernel.org/r/ec06d0ab340e8460d293772faba19ad8a5c371aa.1624372313.git.bristot@redhat.com

Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 Documentation/trace/hwlat_detector.rst |   3 +-
 kernel/trace/trace_hwlat.c             | 186 ++++++++++++++++++++-----
 2 files changed, 152 insertions(+), 37 deletions(-)

diff --git a/Documentation/trace/hwlat_detector.rst b/Documentation/trace/hwlat_detector.rst
index 4d952df0586a..de94b499b0bc 100644
--- a/Documentation/trace/hwlat_detector.rst
+++ b/Documentation/trace/hwlat_detector.rst
@@ -78,10 +78,11 @@ in /sys/kernel/tracing:
  - hwlat_detector/window	- amount of time between (width) runs (usecs)
  - hwlat_detector/mode	- the thread mode
 
-By default, the hwlat detector's kernel thread will migrate across each CPU
+By default, one hwlat detector's kernel thread will migrate across each CPU
 specified in cpumask at the beginning of a new window, in a round-robin
 fashion. This behavior can be changed by changing the thread mode,
 the available options are:
 
  - none:        do not force migration
  - round-robin: migrate across each CPU specified in cpumask [default]
+ - per-cpu:     create one thread for each cpu in tracing_cpumask
diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index bae74b95cf55..3957b36826e2 100644
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -54,9 +54,6 @@ static struct trace_array	*hwlat_trace;
 #define DEFAULT_SAMPLE_WIDTH	500000			/* 0.5s */
 #define DEFAULT_LAT_THRESHOLD	10			/* 10us */
 
-/* sampling thread*/
-static struct task_struct *hwlat_kthread;
-
 static struct dentry *hwlat_sample_width;	/* sample width us */
 static struct dentry *hwlat_sample_window;	/* sample window us */
 static struct dentry *hwlat_thread_mode;	/* hwlat thread mode */
@@ -64,18 +61,26 @@ static struct dentry *hwlat_thread_mode;	/* hwlat thread mode */
 enum {
 	MODE_NONE = 0,
 	MODE_ROUND_ROBIN,
+	MODE_PER_CPU,
 	MODE_MAX
 };
-static char *thread_mode_str[] = { "none", "round-robin" };
+static char *thread_mode_str[] = { "none", "round-robin", "per-cpu" };
 
 /* Save the previous tracing_thresh value */
 static unsigned long save_tracing_thresh;
 
-/* NMI timestamp counters */
-static u64 nmi_ts_start;
-static u64 nmi_total_ts;
-static int nmi_count;
-static int nmi_cpu;
+/* runtime kthread data */
+struct hwlat_kthread_data {
+	struct task_struct	*kthread;
+	/* NMI timestamp counters */
+	u64			nmi_ts_start;
+	u64			nmi_total_ts;
+	int			nmi_count;
+	int			nmi_cpu;
+};
+
+struct hwlat_kthread_data hwlat_single_cpu_data;
+DEFINE_PER_CPU(struct hwlat_kthread_data, hwlat_per_cpu_data);
 
 /* Tells NMIs to call back to the hwlat tracer to record timestamps */
 bool trace_hwlat_callback_enabled;
@@ -112,6 +117,14 @@ static struct hwlat_data {
 	.thread_mode		= MODE_ROUND_ROBIN
 };
 
+static struct hwlat_kthread_data *get_cpu_data(void)
+{
+	if (hwlat_data.thread_mode == MODE_PER_CPU)
+		return this_cpu_ptr(&hwlat_per_cpu_data);
+	else
+		return &hwlat_single_cpu_data;
+}
+
 static bool hwlat_busy;
 
 static void trace_hwlat_sample(struct hwlat_sample *sample)
@@ -149,7 +162,9 @@ static void trace_hwlat_sample(struct hwlat_sample *sample)
 
 void trace_hwlat_callback(bool enter)
 {
-	if (smp_processor_id() != nmi_cpu)
+	struct hwlat_kthread_data *kdata = get_cpu_data();
+
+	if (!kdata->kthread)
 		return;
 
 	/*
@@ -158,13 +173,13 @@ void trace_hwlat_callback(bool enter)
 	 */
 	if (!IS_ENABLED(CONFIG_GENERIC_SCHED_CLOCK)) {
 		if (enter)
-			nmi_ts_start = time_get();
+			kdata->nmi_ts_start = time_get();
 		else
-			nmi_total_ts += time_get() - nmi_ts_start;
+			kdata->nmi_total_ts += time_get() - kdata->nmi_ts_start;
 	}
 
 	if (enter)
-		nmi_count++;
+		kdata->nmi_count++;
 }
 
 /**
@@ -176,6 +191,7 @@ void trace_hwlat_callback(bool enter)
  */
 static int get_sample(void)
 {
+	struct hwlat_kthread_data *kdata = get_cpu_data();
 	struct trace_array *tr = hwlat_trace;
 	struct hwlat_sample s;
 	time_type start, t1, t2, last_t2;
@@ -188,9 +204,8 @@ static int get_sample(void)
 
 	do_div(thresh, NSEC_PER_USEC); /* modifies interval value */
 
-	nmi_cpu = smp_processor_id();
-	nmi_total_ts = 0;
-	nmi_count = 0;
+	kdata->nmi_total_ts = 0;
+	kdata->nmi_count = 0;
 	/* Make sure NMIs see this first */
 	barrier();
 
@@ -260,15 +275,15 @@ static int get_sample(void)
 		ret = 1;
 
 		/* We read in microseconds */
-		if (nmi_total_ts)
-			do_div(nmi_total_ts, NSEC_PER_USEC);
+		if (kdata->nmi_total_ts)
+			do_div(kdata->nmi_total_ts, NSEC_PER_USEC);
 
 		hwlat_data.count++;
 		s.seqnum = hwlat_data.count;
 		s.duration = sample;
 		s.outer_duration = outer_sample;
-		s.nmi_total_ts = nmi_total_ts;
-		s.nmi_count = nmi_count;
+		s.nmi_total_ts = kdata->nmi_total_ts;
+		s.nmi_count = kdata->nmi_count;
 		s.count = count;
 		trace_hwlat_sample(&s);
 
@@ -364,21 +379,40 @@ static int kthread_fn(void *data)
 }
 
 /*
- * start_kthread - Kick off the hardware latency sampling/detector kthread
+ * stop_stop_kthread - Inform the hardware latency sampling/detector kthread to stop
+ *
+ * This kicks the running hardware latency sampling/detector kernel thread and
+ * tells it to stop sampling now. Use this on unload and at system shutdown.
+ */
+static void stop_single_kthread(void)
+{
+	struct hwlat_kthread_data *kdata = get_cpu_data();
+	struct task_struct *kthread = kdata->kthread;
+
+	if (!kthread)
+		return;
+
+	kthread_stop(kthread);
+	kdata->kthread = NULL;
+}
+
+
+/*
+ * start_single_kthread - Kick off the hardware latency sampling/detector kthread
  *
  * This starts the kernel thread that will sit and sample the CPU timestamp
  * counter (TSC or similar) and look for potential hardware latencies.
  */
-static int start_kthread(struct trace_array *tr)
+static int start_single_kthread(struct trace_array *tr)
 {
+	struct hwlat_kthread_data *kdata = get_cpu_data();
 	struct cpumask *current_mask = &save_cpumask;
 	struct task_struct *kthread;
 	int next_cpu;
 
-	if (hwlat_kthread)
+	if (kdata->kthread)
 		return 0;
 
-
 	kthread = kthread_create(kthread_fn, NULL, "hwlatd");
 	if (IS_ERR(kthread)) {
 		pr_err(BANNER "could not start sampling thread\n");
@@ -400,24 +434,97 @@ static int start_kthread(struct trace_array *tr)
 
 	sched_setaffinity(kthread->pid, current_mask);
 
-	hwlat_kthread = kthread;
+	kdata->kthread = kthread;
 	wake_up_process(kthread);
 
 	return 0;
 }
 
 /*
- * stop_kthread - Inform the hardware latency sampling/detector kthread to stop
+ * stop_cpu_kthread - Stop a hwlat cpu kthread
+ */
+static void stop_cpu_kthread(unsigned int cpu)
+{
+	struct task_struct *kthread;
+
+	kthread = per_cpu(hwlat_per_cpu_data, cpu).kthread;
+	if (kthread)
+		kthread_stop(kthread);
+}
+
+/*
+ * stop_per_cpu_kthreads - Inform the hardware latency sampling/detector kthread to stop
  *
- * This kicks the running hardware latency sampling/detector kernel thread and
+ * This kicks the running hardware latency sampling/detector kernel threads and
  * tells it to stop sampling now. Use this on unload and at system shutdown.
  */
-static void stop_kthread(void)
+static void stop_per_cpu_kthreads(void)
 {
-	if (!hwlat_kthread)
-		return;
-	kthread_stop(hwlat_kthread);
-	hwlat_kthread = NULL;
+	unsigned int cpu;
+
+	get_online_cpus();
+	for_each_online_cpu(cpu)
+		stop_cpu_kthread(cpu);
+	put_online_cpus();
+}
+
+/*
+ * start_cpu_kthread - Start a hwlat cpu kthread
+ */
+static int start_cpu_kthread(unsigned int cpu)
+{
+	struct task_struct *kthread;
+	char comm[24];
+
+	snprintf(comm, 24, "hwlatd/%d", cpu);
+
+	kthread = kthread_create_on_cpu(kthread_fn, NULL, cpu, comm);
+	if (IS_ERR(kthread)) {
+		pr_err(BANNER "could not start sampling thread\n");
+		return -ENOMEM;
+	}
+
+	per_cpu(hwlat_per_cpu_data, cpu).kthread = kthread;
+	wake_up_process(kthread);
+
+	return 0;
+}
+
+/*
+ * start_per_cpu_kthreads - Kick off the hardware latency sampling/detector kthreads
+ *
+ * This starts the kernel threads that will sit on potentially all cpus and
+ * sample the CPU timestamp counter (TSC or similar) and look for potential
+ * hardware latencies.
+ */
+static int start_per_cpu_kthreads(struct trace_array *tr)
+{
+	struct cpumask *current_mask = &save_cpumask;
+	unsigned int cpu;
+	int retval;
+
+	get_online_cpus();
+	/*
+	 * Run only on CPUs in which hwlat is allowed to run.
+	 */
+	cpumask_and(current_mask, cpu_online_mask, tr->tracing_cpumask);
+
+	for_each_online_cpu(cpu)
+		per_cpu(hwlat_per_cpu_data, cpu).kthread = NULL;
+
+	for_each_cpu(cpu, current_mask) {
+		retval = start_cpu_kthread(cpu);
+		if (retval)
+			goto out_error;
+	}
+	put_online_cpus();
+
+	return 0;
+
+out_error:
+	put_online_cpus();
+	stop_per_cpu_kthreads();
+	return retval;
 }
 
 /*
@@ -600,7 +707,8 @@ static void hwlat_tracer_stop(struct trace_array *tr);
  * The "none" sets the allowed cpumask for a single hwlatd thread at the
  * startup and lets the scheduler handle the migration. The default mode is
  * the "round-robin" one, in which a single hwlatd thread runs, migrating
- * among the allowed CPUs in a round-robin fashion.
+ * among the allowed CPUs in a round-robin fashion. The "per-cpu" mode
+ * creates one hwlatd thread per allowed CPU.
  */
 static ssize_t hwlat_mode_write(struct file *filp, const char __user *ubuf,
 				 size_t cnt, loff_t *ppos)
@@ -724,14 +832,20 @@ static void hwlat_tracer_start(struct trace_array *tr)
 {
 	int err;
 
-	err = start_kthread(tr);
+	if (hwlat_data.thread_mode == MODE_PER_CPU)
+		err = start_per_cpu_kthreads(tr);
+	else
+		err = start_single_kthread(tr);
 	if (err)
 		pr_err(BANNER "Cannot start hwlat kthread\n");
 }
 
 static void hwlat_tracer_stop(struct trace_array *tr)
 {
-	stop_kthread();
+	if (hwlat_data.thread_mode == MODE_PER_CPU)
+		stop_per_cpu_kthreads();
+	else
+		stop_single_kthread();
 }
 
 static int hwlat_tracer_init(struct trace_array *tr)
@@ -760,7 +874,7 @@ static int hwlat_tracer_init(struct trace_array *tr)
 
 static void hwlat_tracer_reset(struct trace_array *tr)
 {
-	stop_kthread();
+	hwlat_tracer_stop(tr);
 
 	/* the tracing threshold is static between runs */
 	last_tracing_thresh = tracing_thresh;
-- 
2.30.2

[for-next][PATCH 15/24] trace: Add a generic function to read/write u64 values from tracefs

[Steven Rostedt]

From: Daniel Bristot de Oliveira <bristot@redhat.com>

The hwlat detector and (in preparation for) the osnoise/timerlat tracers
have a set of u64 parameters that the user can read/write via tracefs.
For instance, we have hwlat_detector's window and width.

To reduce the code duplication, hwlat's window and width share the same
read function. However, they do not share the write functions because
they do different parameter checks. For instance, the width needs to
be smaller than the window, while the window needs to be larger
than the window. The same pattern repeats on osnoise/timerlat, and
a large portion of the code was devoted to the write function.

Despite having different checks, the write functions have the same
structure:

   read a user-space buffer
   take the lock that protects the value
   check for minimum and maximum acceptable values
      save the value
   release the lock
   return success or error

To reduce the code duplication also in the write functions, this patch
provides a generic read and write implementation for u64 values that
need to be within some minimum and/or maximum parameters, while
(potentially) being protected by a lock.

To use this interface, the structure trace_min_max_param needs to be
filled:

 struct trace_min_max_param {
         struct mutex    *lock;
         u64             *val;
         u64             *min;
         u64             *max;
 };

The desired value is stored on the variable pointed by *val. If *min
points to a minimum acceptable value, it will be checked during the
write operation. Likewise, if *max points to a maximum allowable value,
it will be checked during the write operation. Finally, if *lock points
to a mutex, it will be taken at the beginning of the operation and
released at the end.

The definition of a trace_min_max_param needs to passed as the
(private) *data for tracefs_create_file(), and the trace_min_max_fops
(added by this patch) as the *fops file_operations.

Link: https://lkml.kernel.org/r/3e35760a7c8b5c55f16ae5ad5fc54a0e71cbe647.1624372313.git.bristot@redhat.com

Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace.c | 85 ++++++++++++++++++++++++++++++++++++++++++++
 kernel/trace/trace.h | 18 ++++++++++
 2 files changed, 103 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d352fb4b7709..27bf203ef05a 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7583,6 +7583,91 @@ static const struct file_operations snapshot_raw_fops = {
 
 #endif /* CONFIG_TRACER_SNAPSHOT */
 
+/*
+ * trace_min_max_write - Write a u64 value to a trace_min_max_param struct
+ * @filp: The active open file structure
+ * @ubuf: The userspace provided buffer to read value into
+ * @cnt: The maximum number of bytes to read
+ * @ppos: The current "file" position
+ *
+ * This function implements the write interface for a struct trace_min_max_param.
+ * The filp->private_data must point to a trace_min_max_param structure that
+ * defines where to write the value, the min and the max acceptable values,
+ * and a lock to protect the write.
+ */
+static ssize_t
+trace_min_max_write(struct file *filp, const char __user *ubuf, size_t cnt, loff_t *ppos)
+{
+	struct trace_min_max_param *param = filp->private_data;
+	u64 val;
+	int err;
+
+	if (!param)
+		return -EFAULT;
+
+	err = kstrtoull_from_user(ubuf, cnt, 10, &val);
+	if (err)
+		return err;
+
+	if (param->lock)
+		mutex_lock(param->lock);
+
+	if (param->min && val < *param->min)
+		err = -EINVAL;
+
+	if (param->max && val > *param->max)
+		err = -EINVAL;
+
+	if (!err)
+		*param->val = val;
+
+	if (param->lock)
+		mutex_unlock(param->lock);
+
+	if (err)
+		return err;
+
+	return cnt;
+}
+
+/*
+ * trace_min_max_read - Read a u64 value from a trace_min_max_param struct
+ * @filp: The active open file structure
+ * @ubuf: The userspace provided buffer to read value into
+ * @cnt: The maximum number of bytes to read
+ * @ppos: The current "file" position
+ *
+ * This function implements the read interface for a struct trace_min_max_param.
+ * The filp->private_data must point to a trace_min_max_param struct with valid
+ * data.
+ */
+static ssize_t
+trace_min_max_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
+{
+	struct trace_min_max_param *param = filp->private_data;
+	char buf[U64_STR_SIZE];
+	int len;
+	u64 val;
+
+	if (!param)
+		return -EFAULT;
+
+	val = *param->val;
+
+	if (cnt > sizeof(buf))
+		cnt = sizeof(buf);
+
+	len = snprintf(buf, sizeof(buf), "%llu\n", val);
+
+	return simple_read_from_buffer(ubuf, cnt, ppos, buf, len);
+}
+
+const struct file_operations trace_min_max_fops = {
+	.open		= tracing_open_generic,
+	.read		= trace_min_max_read,
+	.write		= trace_min_max_write,
+};
+
 #define TRACING_LOG_ERRS_MAX	8
 #define TRACING_LOG_LOC_MAX	128
 
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index cd80d046c7a5..22f8c652ef8b 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1952,4 +1952,22 @@ static inline bool is_good_name(const char *name)
 	return true;
 }
 
+/*
+ * This is a generic way to read and write a u64 value from a file in tracefs.
+ *
+ * The value is stored on the variable pointed by *val. The value needs
+ * to be at least *min and at most *max. The write is protected by an
+ * existing *lock.
+ */
+struct trace_min_max_param {
+	struct mutex	*lock;
+	u64		*val;
+	u64		*min;
+	u64		*max;
+};
+
+#define U64_STR_SIZE		24	/* 20 digits max */
+
+extern const struct file_operations trace_min_max_fops;
+
 #endif /* _LINUX_KERNEL_TRACE_H */
-- 
2.30.2

[for-next][PATCH 16/24] trace/hwlat: Use trace_min_max_param for width and window params

[Steven Rostedt]

From: Daniel Bristot de Oliveira <bristot@redhat.com>

Use the trace_min_max_param to reduce code duplication.

No functional change.

Link: https://lkml.kernel.org/r/b91accd5a7c6c14ea02d3379aae974ba22b47dd6.1624372313.git.bristot@redhat.com

Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace_hwlat.c | 145 ++++++-------------------------------
 1 file changed, 24 insertions(+), 121 deletions(-)

diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index 3957b36826e2..44f46bc1140f 100644
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -527,115 +527,6 @@ static int start_per_cpu_kthreads(struct trace_array *tr)
 	return retval;
 }
 
-/*
- * hwlat_read - Wrapper read function for reading both window and width
- * @filp: The active open file structure
- * @ubuf: The userspace provided buffer to read value into
- * @cnt: The maximum number of bytes to read
- * @ppos: The current "file" position
- *
- * This function provides a generic read implementation for the global state
- * "hwlat_data" structure filesystem entries.
- */
-static ssize_t hwlat_read(struct file *filp, char __user *ubuf,
-			  size_t cnt, loff_t *ppos)
-{
-	char buf[U64STR_SIZE];
-	u64 *entry = filp->private_data;
-	u64 val;
-	int len;
-
-	if (!entry)
-		return -EFAULT;
-
-	if (cnt > sizeof(buf))
-		cnt = sizeof(buf);
-
-	val = *entry;
-
-	len = snprintf(buf, sizeof(buf), "%llu\n", val);
-
-	return simple_read_from_buffer(ubuf, cnt, ppos, buf, len);
-}
-
-/**
- * hwlat_width_write - Write function for "width" 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
- *
- * This function provides a write implementation for the "width" interface
- * to the hardware latency detector. It can be used to configure
- * for how many us of the total window us we will actively sample for any
- * hardware-induced latency periods. Obviously, it is not possible to
- * sample constantly and have the system respond to a sample reader, or,
- * worse, without having the system appear to have gone out to lunch. It
- * is enforced that width is less that the total window size.
- */
-static ssize_t
-hwlat_width_write(struct file *filp, const char __user *ubuf,
-		  size_t cnt, loff_t *ppos)
-{
-	u64 val;
-	int err;
-
-	err = kstrtoull_from_user(ubuf, cnt, 10, &val);
-	if (err)
-		return err;
-
-	mutex_lock(&hwlat_data.lock);
-	if (val < hwlat_data.sample_window)
-		hwlat_data.sample_width = val;
-	else
-		err = -EINVAL;
-	mutex_unlock(&hwlat_data.lock);
-
-	if (err)
-		return err;
-
-	return cnt;
-}
-
-/**
- * hwlat_window_write - Write function for "window" 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
- *
- * This function provides a write implementation for the "window" interface
- * to the hardware latency detector. The window is the total time
- * in us that will be considered one sample period. Conceptually, windows
- * occur back-to-back and contain a sample width period during which
- * actual sampling occurs. Can be used to write a new total window size. It
- * is enforced that any value written must be greater than the sample width
- * size, or an error results.
- */
-static ssize_t
-hwlat_window_write(struct file *filp, const char __user *ubuf,
-		   size_t cnt, loff_t *ppos)
-{
-	u64 val;
-	int err;
-
-	err = kstrtoull_from_user(ubuf, cnt, 10, &val);
-	if (err)
-		return err;
-
-	mutex_lock(&hwlat_data.lock);
-	if (hwlat_data.sample_width < val)
-		hwlat_data.sample_window = val;
-	else
-		err = -EINVAL;
-	mutex_unlock(&hwlat_data.lock);
-
-	if (err)
-		return err;
-
-	return cnt;
-}
-
 static void *s_mode_start(struct seq_file *s, loff_t *pos)
 {
 	int mode = *pos;
@@ -760,16 +651,28 @@ static ssize_t hwlat_mode_write(struct file *filp, const char __user *ubuf,
 	return ret;
 }
 
-static const struct file_operations width_fops = {
-	.open		= tracing_open_generic,
-	.read		= hwlat_read,
-	.write		= hwlat_width_write,
+/*
+ * The width parameter is read/write using the generic trace_min_max_param
+ * method. The *val is protected by the hwlat_data lock and is upper
+ * bounded by the window parameter.
+ */
+static struct trace_min_max_param hwlat_width = {
+	.lock		= &hwlat_data.lock,
+	.val		= &hwlat_data.sample_width,
+	.max		= &hwlat_data.sample_window,
+	.min		= NULL,
 };
 
-static const struct file_operations window_fops = {
-	.open		= tracing_open_generic,
-	.read		= hwlat_read,
-	.write		= hwlat_window_write,
+/*
+ * The window parameter is read/write using the generic trace_min_max_param
+ * method. The *val is protected by the hwlat_data lock and is lower
+ * bounded by the width parameter.
+ */
+static struct trace_min_max_param hwlat_window = {
+	.lock		= &hwlat_data.lock,
+	.val		= &hwlat_data.sample_window,
+	.max		= NULL,
+	.min		= &hwlat_data.sample_width,
 };
 
 static const struct file_operations thread_mode_fops = {
@@ -802,15 +705,15 @@ static int init_tracefs(void)
 
 	hwlat_sample_window = tracefs_create_file("window", 0640,
 						  top_dir,
-						  &hwlat_data.sample_window,
-						  &window_fops);
+						  &hwlat_window,
+						  &trace_min_max_fops);
 	if (!hwlat_sample_window)
 		goto err;
 
 	hwlat_sample_width = tracefs_create_file("width", 0644,
 						 top_dir,
-						 &hwlat_data.sample_width,
-						 &width_fops);
+						 &hwlat_width,
+						 &trace_min_max_fops);
 	if (!hwlat_sample_width)
 		goto err;
 
-- 
2.30.2

[for-next][PATCH 17/24] trace/hwlat: Remove printk from sampling loop

[Steven Rostedt]

From: Daniel Bristot de Oliveira <bristot@redhat.com>

hwlat has some time operation checks on the sample loop, and it is
currently using pr_err (printk) to report them. The problem is that
this can lead the system to an unresponsible state due to an overflow of
printk messages. This problem can be mitigated by writing the error
message to the trace buffer.

Remove the printk messages from the sampling loop, switching the to
messages in the trace buffer.

No functional change.

Link: https://lkml.kernel.org/r/9d77c34869748aa105e965c769d24642914eea3a.1624372313.git.bristot@redhat.com

Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace_hwlat.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index 44f46bc1140f..a625bfdb844e 100644
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -182,6 +182,15 @@ void trace_hwlat_callback(bool enter)
 		kdata->nmi_count++;
 }
 
+/*
+ * hwlat_err - report a hwlat error.
+ */
+#define hwlat_err(msg) ({							\
+	struct trace_array *tr = hwlat_trace;					\
+										\
+	trace_array_printk_buf(tr->array_buffer.buffer, _THIS_IP_, msg);	\
+})
+
 /**
  * get_sample - sample the CPU TSC and look for likely hardware latencies
  *
@@ -225,7 +234,7 @@ static int get_sample(void)
 			outer_diff = time_to_us(time_sub(t1, last_t2));
 			/* This shouldn't happen */
 			if (outer_diff < 0) {
-				pr_err(BANNER "time running backwards\n");
+				hwlat_err(BANNER "time running backwards\n");
 				goto out;
 			}
 			if (outer_diff > outer_sample)
@@ -237,7 +246,7 @@ static int get_sample(void)
 
 		/* Check for possible overflows */
 		if (total < last_total) {
-			pr_err("Time total overflowed\n");
+			hwlat_err("Time total overflowed\n");
 			break;
 		}
 		last_total = total;
@@ -253,7 +262,7 @@ static int get_sample(void)
 
 		/* This shouldn't happen */
 		if (diff < 0) {
-			pr_err(BANNER "time running backwards\n");
+			hwlat_err(BANNER "time running backwards\n");
 			goto out;
 		}
 
-- 
2.30.2

[for-next][PATCH 18/24] trace: Add __print_ns_to_secs() and __print_ns_without_secs() helpers

[Steven Rostedt]

From: Steven Rostedt <rostedt@goodmis.org>

To have nanosecond output displayed in a more human readable format, its
nicer to convert it to a seconds format (XXX.YYYYYYYYY). The problem is that
to do so, the numbers must be divided by NSEC_PER_SEC, and moded too. But as
these numbers are 64 bit, this can not be done simply with '/' and '%'
operators, but must use do_div() instead.

Instead of performing the expensive do_div() in the hot path of the
tracepoint, it is more efficient to perform it during the output phase. But
passing in do_div() can confuse the parser, and do_div() doesn't work
exactly like a normal C function. It modifies the number in place, and we
don't want to modify the actual values in the ring buffer.

Two helper functions are now created:

  __print_ns_to_secs() and __print_ns_without_secs()

They both take a value of nanoseconds, and the former will return that
number divided by NSEC_PER_SEC, and the latter will mod it with NSEC_PER_SEC
giving a way to print a nice human readable format:

 __print_fmt("time=%llu.%09u",
	__print_ns_to_secs(REC->nsec_val),
	__print_ns_without_secs(REC->nsec_val))

Link: https://lkml.kernel.org/r/e503b903045496c4ccde52843e1e318b422f7a56.1624372313.git.bristot@redhat.com

Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/trace/trace_events.h | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/include/trace/trace_events.h b/include/trace/trace_events.h
index 8268bf747d6f..acc17194c160 100644
--- a/include/trace/trace_events.h
+++ b/include/trace/trace_events.h
@@ -358,6 +358,21 @@ TRACE_MAKE_SYSTEM_STR();
 	trace_print_hex_dump_seq(p, prefix_str, prefix_type,		\
 				 rowsize, groupsize, buf, len, ascii)
 
+#undef __print_ns_to_secs
+#define __print_ns_to_secs(value)			\
+	({						\
+		u64 ____val = (u64)(value);		\
+		do_div(____val, NSEC_PER_SEC);		\
+		____val;				\
+	})
+
+#undef __print_ns_without_secs
+#define __print_ns_without_secs(value)			\
+	({						\
+		u64 ____val = (u64)(value);		\
+		(u32) do_div(____val, NSEC_PER_SEC);	\
+	})
+
 #undef DECLARE_EVENT_CLASS
 #define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print)	\
 static notrace enum print_line_t					\
@@ -736,6 +751,16 @@ static inline void ftrace_test_probe_##call(void)			\
 #undef __print_array
 #undef __print_hex_dump
 
+/*
+ * The below is not executed in the kernel. It is only what is
+ * displayed in the print format for userspace to parse.
+ */
+#undef __print_ns_to_secs
+#define __print_ns_to_secs(val) (val) / 1000000000UL
+
+#undef __print_ns_without_secs
+#define __print_ns_without_secs(val) (val) % 1000000000UL
+
 #undef TP_printk
 #define TP_printk(fmt, args...) "\"" fmt "\", "  __stringify(args)
 
-- 
2.30.2

[for-next][PATCH 20/24] trace: Add osnoise tracer

[Steven Rostedt]

From: Daniel Bristot de Oliveira <bristot@redhat.com>

In the context of high-performance computing (HPC), the Operating System
Noise (*osnoise*) refers to the interference experienced by an application
due to activities inside the operating system. In the context of Linux,
NMIs, IRQs, SoftIRQs, and any other system thread can cause noise to the
system. Moreover, hardware-related jobs can also cause noise, for example,
via SMIs.

The osnoise tracer leverages the hwlat_detector by running a similar
loop with preemption, SoftIRQs and IRQs enabled, thus allowing all
the sources of *osnoise* during its execution. Using the same approach
of hwlat, osnoise takes note of the entry and exit point of any
source of interferences, increasing a per-cpu interference counter. The
osnoise tracer also saves an interference counter for each source of
interference. The interference counter for NMI, IRQs, SoftIRQs, and
threads is increased anytime the tool observes these interferences' entry
events. When a noise happens without any interference from the operating
system level, the hardware noise counter increases, pointing to a
hardware-related noise. In this way, osnoise can account for any
source of interference. At the end of the period, the osnoise tracer
prints the sum of all noise, the max single noise, the percentage of CPU
available for the thread, and the counters for the noise sources.

Usage

Write the ASCII text "osnoise" into the current_tracer file of the
tracing system (generally mounted at /sys/kernel/tracing).

For example::

        [root@f32 ~]# cd /sys/kernel/tracing/
        [root@f32 tracing]# echo osnoise > current_tracer

It is possible to follow the trace by reading the trace trace file::

        [root@f32 tracing]# cat trace
        # tracer: osnoise
        #
        #                                _-----=> irqs-off
        #                               / _----=> need-resched
        #                              | / _---=> hardirq/softirq
        #                              || / _--=> preempt-depth                            MAX
        #                              || /                                             SINGLE     Interference counters:
        #                              ||||               RUNTIME      NOISE   % OF CPU  NOISE    +-----------------------------+
        #           TASK-PID      CPU# ||||   TIMESTAMP    IN US       IN US  AVAILABLE  IN US     HW    NMI    IRQ   SIRQ THREAD
        #              | |         |   ||||      |           |             |    |            |      |      |      |      |      |
                   <...>-859     [000] ....    81.637220: 1000000        190  99.98100       9     18      0   1007     18      1
                   <...>-860     [001] ....    81.638154: 1000000        656  99.93440      74     23      0   1006     16      3
                   <...>-861     [002] ....    81.638193: 1000000       5675  99.43250     202      6      0   1013     25     21
                   <...>-862     [003] ....    81.638242: 1000000        125  99.98750      45      1      0   1011     23      0
                   <...>-863     [004] ....    81.638260: 1000000       1721  99.82790     168      7      0   1002     49     41
                   <...>-864     [005] ....    81.638286: 1000000        263  99.97370      57      6      0   1006     26      2
                   <...>-865     [006] ....    81.638302: 1000000        109  99.98910      21      3      0   1006     18      1
                   <...>-866     [007] ....    81.638326: 1000000       7816  99.21840     107      8      0   1016     39     19

In addition to the regular trace fields (from TASK-PID to TIMESTAMP), the
tracer prints a message at the end of each period for each CPU that is
running an osnoise/CPU thread. The osnoise specific fields report:

 - The RUNTIME IN USE reports the amount of time in microseconds that
   the osnoise thread kept looping reading the time.
 - The NOISE IN US reports the sum of noise in microseconds observed
   by the osnoise tracer during the associated runtime.
 - The % OF CPU AVAILABLE reports the percentage of CPU available for
   the osnoise thread during the runtime window.
 - The MAX SINGLE NOISE IN US reports the maximum single noise observed
   during the runtime window.
 - The Interference counters display how many each of the respective
   interference happened during the runtime window.

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

The tracer has a set of options inside the osnoise directory, they are:

 - osnoise/cpus: CPUs at which a osnoise thread will execute.
 - osnoise/period_us: the period of the osnoise thread.
 - osnoise/runtime_us: how long an osnoise thread will look for noise.
 - osnoise/stop_tracing_us: stop the system tracing if a single noise
   higher than the configured value happens. Writing 0 disables this
   option.
 - osnoise/stop_tracing_total_us: stop the system tracing if total noise
   higher than the configured value happens. Writing 0 disables this
   option.
 - 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.

Additional Tracing

In addition to the tracer, a set of tracepoints were added to
facilitate the identification of the osnoise source.

 - osnoise:sample_threshold: printed anytime a noise is higher than
   the configurable tolerance_ns.
 - osnoise:nmi_noise: noise from NMI, including the duration.
 - osnoise:irq_noise: noise from an IRQ, including the duration.
 - osnoise:softirq_noise: noise from a SoftIRQ, including the
   duration.
 - osnoise:thread_noise: noise from a thread, including the duration.

Note that all the values are *net values*. For example, if while osnoise
is running, another thread preempts the osnoise thread, it will start a
thread_noise duration at the start. Then, an IRQ takes place, preempting
the thread_noise, starting a irq_noise. When the IRQ ends its execution,
it will compute its duration, and this duration will be subtracted from
the thread_noise, in such a way as to avoid the double accounting of the
IRQ execution. This logic is valid for all sources of noise.

Here is one example of the usage of these tracepoints::

       osnoise/8-961     [008] d.h.  5789.857532: irq_noise: local_timer:236 start 5789.857529929 duration 1845 ns
       osnoise/8-961     [008] dNh.  5789.858408: irq_noise: local_timer:236 start 5789.858404871 duration 2848 ns
     migration/8-54      [008] d...  5789.858413: thread_noise: migration/8:54 start 5789.858409300 duration 3068 ns
       osnoise/8-961     [008] ....  5789.858413: sample_threshold: start 5789.858404555 duration 8723 ns interferences 2

In this example, a noise sample of 8 microseconds was reported in the last
line, pointing to two interferences. Looking backward in the trace, the
two previous entries were about the migration thread running after a
timer IRQ execution. The first event is not part of the noise because
it took place one millisecond before.

It is worth noticing that the sum of the duration reported in the
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.

Link: https://lkml.kernel.org/r/e649467042d60e7b62714c9c6751a56299d15119.1624372313.git.bristot@redhat.com

Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
[
  Made the following functions static:
   trace_irqentry_callback()
   trace_irqexit_callback()
   trace_intel_irqentry_callback()
   trace_intel_irqexit_callback()

  Added to include/trace.h:
   osnoise_arch_register()
   osnoise_arch_unregister()

  Fixed define logic for LATENCY_FS_NOTIFY

  Reported-by: kernel test robot <lkp@intel.com>
]
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 Documentation/trace/index.rst          |    1 +
 Documentation/trace/osnoise-tracer.rst |  152 +++
 arch/x86/kernel/Makefile               |    1 +
 arch/x86/kernel/trace.c                |  237 ++++
 include/linux/ftrace_irq.h             |   13 +
 include/linux/trace.h                  |    5 +
 include/trace/events/osnoise.h         |  142 +++
 kernel/trace/Kconfig                   |   34 +
 kernel/trace/Makefile                  |    1 +
 kernel/trace/trace.h                   |    9 +-
 kernel/trace/trace_entries.h           |   25 +
 kernel/trace/trace_osnoise.c           | 1384 ++++++++++++++++++++++++
 kernel/trace/trace_output.c            |   72 +-
 13 files changed, 2072 insertions(+), 4 deletions(-)
 create mode 100644 Documentation/trace/osnoise-tracer.rst
 create mode 100644 arch/x86/kernel/trace.c
 create mode 100644 include/trace/events/osnoise.h
 create mode 100644 kernel/trace/trace_osnoise.c

diff --git a/Documentation/trace/index.rst b/Documentation/trace/index.rst
index f634b36fd3aa..608107b27cc0 100644
--- a/Documentation/trace/index.rst
+++ b/Documentation/trace/index.rst
@@ -23,6 +23,7 @@ Linux Tracing Technologies
    histogram-design
    boottime-trace
    hwlat_detector
+   osnoise-tracer
    intel_th
    ring-buffer-design
    stm
diff --git a/Documentation/trace/osnoise-tracer.rst b/Documentation/trace/osnoise-tracer.rst
new file mode 100644
index 000000000000..37a3c10fb216
--- /dev/null
+++ b/Documentation/trace/osnoise-tracer.rst
@@ -0,0 +1,152 @@
+==============
+OSNOISE Tracer
+==============
+
+In the context of high-performance computing (HPC), the Operating System
+Noise (*osnoise*) refers to the interference experienced by an application
+due to activities inside the operating system. In the context of Linux,
+NMIs, IRQs, SoftIRQs, and any other system thread can cause noise to the
+system. Moreover, hardware-related jobs can also cause noise, for example,
+via SMIs.
+
+hwlat_detector is one of the tools used to identify the most complex
+source of noise: *hardware noise*.
+
+In a nutshell, the hwlat_detector creates a thread that runs
+periodically for a given period. At the beginning of a period, the thread
+disables interrupt and starts sampling. While running, the hwlatd
+thread reads the time in a loop. As interrupts are disabled, threads,
+IRQs, and SoftIRQs cannot interfere with the hwlatd thread. Hence, the
+cause of any gap between two different reads of the time roots either on
+NMI or in the hardware itself. At the end of the period, hwlatd enables
+interrupts and reports the max observed gap between the reads. It also
+prints a NMI occurrence counter. If the output does not report NMI
+executions, the user can conclude that the hardware is the culprit for
+the latency. The hwlat detects the NMI execution by observing
+the entry and exit of a NMI.
+
+The osnoise tracer leverages the hwlat_detector by running a
+similar loop with preemption, SoftIRQs and IRQs enabled, thus allowing
+all the sources of *osnoise* during its execution. Using the same approach
+of hwlat, osnoise takes note of the entry and exit point of any
+source of interferences, increasing a per-cpu interference counter. The
+osnoise tracer also saves an interference counter for each source of
+interference. The interference counter for NMI, IRQs, SoftIRQs, and
+threads is increased anytime the tool observes these interferences' entry
+events. When a noise happens without any interference from the operating
+system level, the hardware noise counter increases, pointing to a
+hardware-related noise. In this way, osnoise can account for any
+source of interference. At the end of the period, the osnoise tracer
+prints the sum of all noise, the max single noise, the percentage of CPU
+available for the thread, and the counters for the noise sources.
+
+Usage
+-----
+
+Write the ASCII text "osnoise" into the current_tracer file of the
+tracing system (generally mounted at /sys/kernel/tracing).
+
+For example::
+
+        [root@f32 ~]# cd /sys/kernel/tracing/
+        [root@f32 tracing]# echo osnoise > current_tracer
+
+It is possible to follow the trace by reading the trace trace file::
+
+        [root@f32 tracing]# cat trace
+        # tracer: osnoise
+        #
+        #                                _-----=> irqs-off
+        #                               / _----=> need-resched
+        #                              | / _---=> hardirq/softirq
+        #                              || / _--=> preempt-depth                            MAX
+        #                              || /                                             SINGLE     Interference counters:
+        #                              ||||               RUNTIME      NOISE   % OF CPU  NOISE    +-----------------------------+
+        #           TASK-PID      CPU# ||||   TIMESTAMP    IN US       IN US  AVAILABLE  IN US     HW    NMI    IRQ   SIRQ THREAD
+        #              | |         |   ||||      |           |             |    |            |      |      |      |      |      |
+                   <...>-859     [000] ....    81.637220: 1000000        190  99.98100       9     18      0   1007     18      1
+                   <...>-860     [001] ....    81.638154: 1000000        656  99.93440      74     23      0   1006     16      3
+                   <...>-861     [002] ....    81.638193: 1000000       5675  99.43250     202      6      0   1013     25     21
+                   <...>-862     [003] ....    81.638242: 1000000        125  99.98750      45      1      0   1011     23      0
+                   <...>-863     [004] ....    81.638260: 1000000       1721  99.82790     168      7      0   1002     49     41
+                   <...>-864     [005] ....    81.638286: 1000000        263  99.97370      57      6      0   1006     26      2
+                   <...>-865     [006] ....    81.638302: 1000000        109  99.98910      21      3      0   1006     18      1
+                   <...>-866     [007] ....    81.638326: 1000000       7816  99.21840     107      8      0   1016     39     19
+
+In addition to the regular trace fields (from TASK-PID to TIMESTAMP), the
+tracer prints a message at the end of each period for each CPU that is
+running an osnoise/ thread. The osnoise specific fields report:
+
+ - The RUNTIME IN USE reports the amount of time in microseconds that
+   the osnoise thread kept looping reading the time.
+ - The NOISE IN US reports the sum of noise in microseconds observed
+   by the osnoise tracer during the associated runtime.
+ - The % OF CPU AVAILABLE reports the percentage of CPU available for
+   the osnoise thread during the runtime window.
+ - The MAX SINGLE NOISE IN US reports the maximum single noise observed
+   during the runtime window.
+ - The Interference counters display how many each of the respective
+   interference happened during the runtime window.
+
+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
+---------------------
+
+The tracer has a set of options inside the osnoise directory, they are:
+
+ - osnoise/cpus: CPUs at which a osnoise thread will execute.
+ - osnoise/period_us: the period of the osnoise thread.
+ - osnoise/runtime_us: how long an osnoise thread will look for noise.
+ - osnoise/stop_tracing_us: stop the system tracing if a single noise
+   higher than the configured value happens. Writing 0 disables this
+   option.
+ - osnoise/stop_tracing_total_us: stop the system tracing if total noise
+   higher than the configured value happens. Writing 0 disables this
+   option.
+ - tracing_threshold: the minimum delta between two time() reads to be
+   considered as noise, in us. When set to 0, the default value will
+   will be used, which is currently 5 us.
+
+Additional Tracing
+------------------
+
+In addition to the tracer, a set of tracepoints were added to
+facilitate the identification of the osnoise source.
+
+ - osnoise:sample_threshold: printed anytime a noise is higher than
+   the configurable tolerance_ns.
+ - osnoise:nmi_noise: noise from NMI, including the duration.
+ - osnoise:irq_noise: noise from an IRQ, including the duration.
+ - osnoise:softirq_noise: noise from a SoftIRQ, including the
+   duration.
+ - osnoise:thread_noise: noise from a thread, including the duration.
+
+Note that all the values are *net values*. For example, if while osnoise
+is running, another thread preempts the osnoise thread, it will start a
+thread_noise duration at the start. Then, an IRQ takes place, preempting
+the thread_noise, starting a irq_noise. When the IRQ ends its execution,
+it will compute its duration, and this duration will be subtracted from
+the thread_noise, in such a way as to avoid the double accounting of the
+IRQ execution. This logic is valid for all sources of noise.
+
+Here is one example of the usage of these tracepoints::
+
+       osnoise/8-961     [008] d.h.  5789.857532: irq_noise: local_timer:236 start 5789.857529929 duration 1845 ns
+       osnoise/8-961     [008] dNh.  5789.858408: irq_noise: local_timer:236 start 5789.858404871 duration 2848 ns
+     migration/8-54      [008] d...  5789.858413: thread_noise: migration/8:54 start 5789.858409300 duration 3068 ns
+       osnoise/8-961     [008] ....  5789.858413: sample_threshold: start 5789.858404555 duration 8812 ns interferences 2
+
+In this example, a noise sample of 8 microseconds was reported in the last
+line, pointing to two interferences. Looking backward in the trace, the
+two previous entries were about the migration thread running after a
+timer IRQ execution. The first event is not part of the noise because
+it took place one millisecond before.
+
+It is worth noticing that the sum of the duration reported in the
+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.
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 0f66682ac02a..3e625c61f008 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -102,6 +102,7 @@ obj-$(CONFIG_FUNCTION_TRACER)	+= ftrace_$(BITS).o
 obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
 obj-$(CONFIG_FTRACE_SYSCALLS)	+= ftrace.o
 obj-$(CONFIG_X86_TSC)		+= trace_clock.o
+obj-$(CONFIG_TRACING)		+= trace.o
 obj-$(CONFIG_CRASH_CORE)	+= crash_core_$(BITS).o
 obj-$(CONFIG_KEXEC_CORE)	+= machine_kexec_$(BITS).o
 obj-$(CONFIG_KEXEC_CORE)	+= relocate_kernel_$(BITS).o crash.o
diff --git a/arch/x86/kernel/trace.c b/arch/x86/kernel/trace.c
new file mode 100644
index 000000000000..6912672c33a7
--- /dev/null
+++ b/arch/x86/kernel/trace.c
@@ -0,0 +1,237 @@
+#include <asm/trace/irq_vectors.h>
+#include <linux/trace.h>
+
+#if defined(CONFIG_OSNOISE_TRACER) && defined(CONFIG_X86_LOCAL_APIC)
+extern void osnoise_trace_irq_entry(int id);
+extern void osnoise_trace_irq_exit(int id, const char *desc);
+
+/*
+ * trace_intel_irq_entry - record intel specific IRQ entry
+ */
+static void trace_intel_irq_entry(void *data, int vector)
+{
+	osnoise_trace_irq_entry(vector);
+}
+
+/*
+ * trace_intel_irq_exit - record intel specific IRQ exit
+ */
+static void trace_intel_irq_exit(void *data, int vector)
+{
+	char *vector_desc = (char *) data;
+
+	osnoise_trace_irq_exit(vector, vector_desc);
+}
+
+/*
+ * register_intel_irq_tp - Register intel specific IRQ entry tracepoints
+ */
+int osnoise_arch_register(void)
+{
+	int ret;
+
+	ret = register_trace_local_timer_entry(trace_intel_irq_entry, NULL);
+	if (ret)
+		goto out_err;
+
+	ret = register_trace_local_timer_exit(trace_intel_irq_exit, "local_timer");
+	if (ret)
+		goto out_timer_entry;
+
+#ifdef CONFIG_X86_THERMAL_VECTOR
+	ret = register_trace_thermal_apic_entry(trace_intel_irq_entry, NULL);
+	if (ret)
+		goto out_timer_exit;
+
+	ret = register_trace_thermal_apic_exit(trace_intel_irq_exit, "thermal_apic");
+	if (ret)
+		goto out_thermal_entry;
+#endif /* CONFIG_X86_THERMAL_VECTOR */
+
+#ifdef CONFIG_X86_MCE_AMD
+	ret = register_trace_deferred_error_apic_entry(trace_intel_irq_entry, NULL);
+	if (ret)
+		goto out_thermal_exit;
+
+	ret = register_trace_deferred_error_apic_exit(trace_intel_irq_exit, "deferred_error");
+	if (ret)
+		goto out_deferred_entry;
+#endif
+
+#ifdef CONFIG_X86_MCE_THRESHOLD
+	ret = register_trace_threshold_apic_entry(trace_intel_irq_entry, NULL);
+	if (ret)
+		goto out_deferred_exit;
+
+	ret = register_trace_threshold_apic_exit(trace_intel_irq_exit, "threshold_apic");
+	if (ret)
+		goto out_threshold_entry;
+#endif /* CONFIG_X86_MCE_THRESHOLD */
+
+#ifdef CONFIG_SMP
+	ret = register_trace_call_function_single_entry(trace_intel_irq_entry, NULL);
+	if (ret)
+		goto out_threshold_exit;
+
+	ret = register_trace_call_function_single_exit(trace_intel_irq_exit,
+						       "call_function_single");
+	if (ret)
+		goto out_call_function_single_entry;
+
+	ret = register_trace_call_function_entry(trace_intel_irq_entry, NULL);
+	if (ret)
+		goto out_call_function_single_exit;
+
+	ret = register_trace_call_function_exit(trace_intel_irq_exit, "call_function");
+	if (ret)
+		goto out_call_function_entry;
+
+	ret = register_trace_reschedule_entry(trace_intel_irq_entry, NULL);
+	if (ret)
+		goto out_call_function_exit;
+
+	ret = register_trace_reschedule_exit(trace_intel_irq_exit, "reschedule");
+	if (ret)
+		goto out_reschedule_entry;
+#endif /* CONFIG_SMP */
+
+#ifdef CONFIG_IRQ_WORK
+	ret = register_trace_irq_work_entry(trace_intel_irq_entry, NULL);
+	if (ret)
+		goto out_reschedule_exit;
+
+	ret = register_trace_irq_work_exit(trace_intel_irq_exit, "irq_work");
+	if (ret)
+		goto out_irq_work_entry;
+#endif
+
+	ret = register_trace_x86_platform_ipi_entry(trace_intel_irq_entry, NULL);
+	if (ret)
+		goto out_irq_work_exit;
+
+	ret = register_trace_x86_platform_ipi_exit(trace_intel_irq_exit, "x86_platform_ipi");
+	if (ret)
+		goto out_x86_ipi_entry;
+
+	ret = register_trace_error_apic_entry(trace_intel_irq_entry, NULL);
+	if (ret)
+		goto out_x86_ipi_exit;
+
+	ret = register_trace_error_apic_exit(trace_intel_irq_exit, "error_apic");
+	if (ret)
+		goto out_error_apic_entry;
+
+	ret = register_trace_spurious_apic_entry(trace_intel_irq_entry, NULL);
+	if (ret)
+		goto out_error_apic_exit;
+
+	ret = register_trace_spurious_apic_exit(trace_intel_irq_exit, "spurious_apic");
+	if (ret)
+		goto out_spurious_apic_entry;
+
+	return 0;
+
+out_spurious_apic_entry:
+	unregister_trace_spurious_apic_entry(trace_intel_irq_entry, NULL);
+out_error_apic_exit:
+	unregister_trace_error_apic_exit(trace_intel_irq_exit, "error_apic");
+out_error_apic_entry:
+	unregister_trace_error_apic_entry(trace_intel_irq_entry, NULL);
+out_x86_ipi_exit:
+	unregister_trace_x86_platform_ipi_exit(trace_intel_irq_exit, "x86_platform_ipi");
+out_x86_ipi_entry:
+	unregister_trace_x86_platform_ipi_entry(trace_intel_irq_entry, NULL);
+out_irq_work_exit:
+
+#ifdef CONFIG_IRQ_WORK
+	unregister_trace_irq_work_exit(trace_intel_irq_exit, "irq_work");
+out_irq_work_entry:
+	unregister_trace_irq_work_entry(trace_intel_irq_entry, NULL);
+out_reschedule_exit:
+#endif
+
+#ifdef CONFIG_SMP
+	unregister_trace_reschedule_exit(trace_intel_irq_exit, "reschedule");
+out_reschedule_entry:
+	unregister_trace_reschedule_entry(trace_intel_irq_entry, NULL);
+out_call_function_exit:
+	unregister_trace_call_function_exit(trace_intel_irq_exit, "call_function");
+out_call_function_entry:
+	unregister_trace_call_function_entry(trace_intel_irq_entry, NULL);
+out_call_function_single_exit:
+	unregister_trace_call_function_single_exit(trace_intel_irq_exit, "call_function_single");
+out_call_function_single_entry:
+	unregister_trace_call_function_single_entry(trace_intel_irq_entry, NULL);
+out_threshold_exit:
+#endif
+
+#ifdef CONFIG_X86_MCE_THRESHOLD
+	unregister_trace_threshold_apic_exit(trace_intel_irq_exit, "threshold_apic");
+out_threshold_entry:
+	unregister_trace_threshold_apic_entry(trace_intel_irq_entry, NULL);
+out_deferred_exit:
+#endif
+
+#ifdef CONFIG_X86_MCE_AMD
+	unregister_trace_deferred_error_apic_exit(trace_intel_irq_exit, "deferred_error");
+out_deferred_entry:
+	unregister_trace_deferred_error_apic_entry(trace_intel_irq_entry, NULL);
+out_thermal_exit:
+#endif /* CONFIG_X86_MCE_AMD */
+
+#ifdef CONFIG_X86_THERMAL_VECTOR
+	unregister_trace_thermal_apic_exit(trace_intel_irq_exit, "thermal_apic");
+out_thermal_entry:
+	unregister_trace_thermal_apic_entry(trace_intel_irq_entry, NULL);
+out_timer_exit:
+#endif /* CONFIG_X86_THERMAL_VECTOR */
+
+	unregister_trace_local_timer_exit(trace_intel_irq_exit, "local_timer");
+out_timer_entry:
+	unregister_trace_local_timer_entry(trace_intel_irq_entry, NULL);
+out_err:
+	return -EINVAL;
+}
+
+void osnoise_arch_unregister(void)
+{
+	unregister_trace_spurious_apic_exit(trace_intel_irq_exit, "spurious_apic");
+	unregister_trace_spurious_apic_entry(trace_intel_irq_entry, NULL);
+	unregister_trace_error_apic_exit(trace_intel_irq_exit, "error_apic");
+	unregister_trace_error_apic_entry(trace_intel_irq_entry, NULL);
+	unregister_trace_x86_platform_ipi_exit(trace_intel_irq_exit, "x86_platform_ipi");
+	unregister_trace_x86_platform_ipi_entry(trace_intel_irq_entry, NULL);
+
+#ifdef CONFIG_IRQ_WORK
+	unregister_trace_irq_work_exit(trace_intel_irq_exit, "irq_work");
+	unregister_trace_irq_work_entry(trace_intel_irq_entry, NULL);
+#endif
+
+#ifdef CONFIG_SMP
+	unregister_trace_reschedule_exit(trace_intel_irq_exit, "reschedule");
+	unregister_trace_reschedule_entry(trace_intel_irq_entry, NULL);
+	unregister_trace_call_function_exit(trace_intel_irq_exit, "call_function");
+	unregister_trace_call_function_entry(trace_intel_irq_entry, NULL);
+	unregister_trace_call_function_single_exit(trace_intel_irq_exit, "call_function_single");
+	unregister_trace_call_function_single_entry(trace_intel_irq_entry, NULL);
+#endif
+
+#ifdef CONFIG_X86_MCE_THRESHOLD
+	unregister_trace_threshold_apic_exit(trace_intel_irq_exit, "threshold_apic");
+	unregister_trace_threshold_apic_entry(trace_intel_irq_entry, NULL);
+#endif
+
+#ifdef CONFIG_X86_MCE_AMD
+	unregister_trace_deferred_error_apic_exit(trace_intel_irq_exit, "deferred_error");
+	unregister_trace_deferred_error_apic_entry(trace_intel_irq_entry, NULL);
+#endif
+
+#ifdef CONFIG_X86_THERMAL_VECTOR
+	unregister_trace_thermal_apic_exit(trace_intel_irq_exit, "thermal_apic");
+	unregister_trace_thermal_apic_entry(trace_intel_irq_entry, NULL);
+#endif /* CONFIG_X86_THERMAL_VECTOR */
+
+	unregister_trace_local_timer_exit(trace_intel_irq_exit, "local_timer");
+	unregister_trace_local_timer_entry(trace_intel_irq_entry, NULL);
+}
+#endif /* CONFIG_OSNOISE_TRAECR && CONFIG_X86_LOCAL_APIC */
diff --git a/include/linux/ftrace_irq.h b/include/linux/ftrace_irq.h
index 0abd9a1d2852..f6faa31289ba 100644
--- a/include/linux/ftrace_irq.h
+++ b/include/linux/ftrace_irq.h
@@ -7,12 +7,21 @@ extern bool trace_hwlat_callback_enabled;
 extern void trace_hwlat_callback(bool enter);
 #endif
 
+#ifdef CONFIG_OSNOISE_TRACER
+extern bool trace_osnoise_callback_enabled;
+extern void trace_osnoise_callback(bool enter);
+#endif
+
 static inline void ftrace_nmi_enter(void)
 {
 #ifdef CONFIG_HWLAT_TRACER
 	if (trace_hwlat_callback_enabled)
 		trace_hwlat_callback(true);
 #endif
+#ifdef CONFIG_OSNOISE_TRACER
+	if (trace_osnoise_callback_enabled)
+		trace_osnoise_callback(true);
+#endif
 }
 
 static inline void ftrace_nmi_exit(void)
@@ -21,6 +30,10 @@ static inline void ftrace_nmi_exit(void)
 	if (trace_hwlat_callback_enabled)
 		trace_hwlat_callback(false);
 #endif
+#ifdef CONFIG_OSNOISE_TRACER
+	if (trace_osnoise_callback_enabled)
+		trace_osnoise_callback(false);
+#endif
 }
 
 #endif /* _LINUX_FTRACE_IRQ_H */
diff --git a/include/linux/trace.h b/include/linux/trace.h
index be1e130ed87c..4e3858640c47 100644
--- a/include/linux/trace.h
+++ b/include/linux/trace.h
@@ -41,6 +41,11 @@ int trace_array_init_printk(struct trace_array *tr);
 void trace_array_put(struct trace_array *tr);
 struct trace_array *trace_array_get_by_name(const char *name);
 int trace_array_destroy(struct trace_array *tr);
+
+/* For osnoise tracer */
+int osnoise_arch_register(void);
+void osnoise_arch_unregister(void);
+
 #endif	/* CONFIG_TRACING */
 
 #endif	/* _LINUX_TRACE_H */
diff --git a/include/trace/events/osnoise.h b/include/trace/events/osnoise.h
new file mode 100644
index 000000000000..28762c69f6c9
--- /dev/null
+++ b/include/trace/events/osnoise.h
@@ -0,0 +1,142 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM osnoise
+
+#if !defined(_OSNOISE_TRACE_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _OSNOISE_TRACE_H
+
+#include <linux/tracepoint.h>
+TRACE_EVENT(thread_noise,
+
+	TP_PROTO(struct task_struct *t, u64 start, u64 duration),
+
+	TP_ARGS(t, start, duration),
+
+	TP_STRUCT__entry(
+		__array(	char,		comm,	TASK_COMM_LEN)
+		__field(	u64,		start	)
+		__field(	u64,		duration)
+		__field(	pid_t,		pid	)
+	),
+
+	TP_fast_assign(
+		memcpy(__entry->comm, t->comm, TASK_COMM_LEN);
+		__entry->pid = t->pid;
+		__entry->start = start;
+		__entry->duration = duration;
+	),
+
+	TP_printk("%8s:%d start %llu.%09u duration %llu ns",
+		__entry->comm,
+		__entry->pid,
+		__print_ns_to_secs(__entry->start),
+		__print_ns_without_secs(__entry->start),
+		__entry->duration)
+);
+
+TRACE_EVENT(softirq_noise,
+
+	TP_PROTO(int vector, u64 start, u64 duration),
+
+	TP_ARGS(vector, start, duration),
+
+	TP_STRUCT__entry(
+		__field(	u64,		start	)
+		__field(	u64,		duration)
+		__field(	int,		vector	)
+	),
+
+	TP_fast_assign(
+		__entry->vector = vector;
+		__entry->start = start;
+		__entry->duration = duration;
+	),
+
+	TP_printk("%8s:%d start %llu.%09u duration %llu ns",
+		show_softirq_name(__entry->vector),
+		__entry->vector,
+		__print_ns_to_secs(__entry->start),
+		__print_ns_without_secs(__entry->start),
+		__entry->duration)
+);
+
+TRACE_EVENT(irq_noise,
+
+	TP_PROTO(int vector, const char *desc, u64 start, u64 duration),
+
+	TP_ARGS(vector, desc, start, duration),
+
+	TP_STRUCT__entry(
+		__field(	u64,		start	)
+		__field(	u64,		duration)
+		__string(	desc,		desc    )
+		__field(	int,		vector	)
+
+	),
+
+	TP_fast_assign(
+		__assign_str(desc, desc);
+		__entry->vector = vector;
+		__entry->start = start;
+		__entry->duration = duration;
+	),
+
+	TP_printk("%s:%d start %llu.%09u duration %llu ns",
+		__get_str(desc),
+		__entry->vector,
+		__print_ns_to_secs(__entry->start),
+		__print_ns_without_secs(__entry->start),
+		__entry->duration)
+);
+
+TRACE_EVENT(nmi_noise,
+
+	TP_PROTO(u64 start, u64 duration),
+
+	TP_ARGS(start, duration),
+
+	TP_STRUCT__entry(
+		__field(	u64,		start	)
+		__field(	u64,		duration)
+	),
+
+	TP_fast_assign(
+		__entry->start = start;
+		__entry->duration = duration;
+	),
+
+	TP_printk("start %llu.%09u duration %llu ns",
+		__print_ns_to_secs(__entry->start),
+		__print_ns_without_secs(__entry->start),
+		__entry->duration)
+);
+
+TRACE_EVENT(sample_threshold,
+
+	TP_PROTO(u64 start, u64 duration, u64 interference),
+
+	TP_ARGS(start, duration, interference),
+
+	TP_STRUCT__entry(
+		__field(	u64,		start	)
+		__field(	u64,		duration)
+		__field(	u64,		interference)
+	),
+
+	TP_fast_assign(
+		__entry->start = start;
+		__entry->duration = duration;
+		__entry->interference = interference;
+	),
+
+	TP_printk("start %llu.%09u duration %llu ns interferences %llu",
+		__print_ns_to_secs(__entry->start),
+		__print_ns_without_secs(__entry->start),
+		__entry->duration,
+		__entry->interference)
+);
+
+#endif /* _TRACE_OSNOISE_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 7fa82778c3e6..41582ae4682b 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -356,6 +356,40 @@ config HWLAT_TRACER
 	 file. Every time a latency is greater than tracing_thresh, it will
 	 be recorded into the ring buffer.
 
+config OSNOISE_TRACER
+	bool "OS Noise tracer"
+	select GENERIC_TRACER
+	help
+	  In the context of high-performance computing (HPC), the Operating
+	  System Noise (osnoise) refers to the interference experienced by an
+	  application due to activities inside the operating system. In the
+	  context of Linux, NMIs, IRQs, SoftIRQs, and any other system thread
+	  can cause noise to the system. Moreover, hardware-related jobs can
+	  also cause noise, for example, via SMIs.
+
+	  The osnoise tracer leverages the hwlat_detector by running a similar
+	  loop with preemption, SoftIRQs and IRQs enabled, thus allowing all
+	  the sources of osnoise during its execution. The osnoise tracer takes
+	  note of the entry and exit point of any source of interferences,
+	  increasing a per-cpu interference counter. It saves an interference
+	  counter for each source of interference. The interference counter for
+	  NMI, IRQs, SoftIRQs, and threads is increased anytime the tool
+	  observes these interferences' entry events. When a noise happens
+	  without any interference from the operating system level, the
+	  hardware noise counter increases, pointing to a hardware-related
+	  noise. In this way, osnoise can account for any source of
+	  interference. At the end of the period, the osnoise tracer prints
+	  the sum of all noise, the max single noise, the percentage of CPU
+	  available for the thread, and the counters for the noise sources.
+
+	  In addition to the tracer, a set of tracepoints were added to
+	  facilitate the identification of the osnoise source.
+
+	  The output will appear in the trace and trace_pipe files.
+
+	  To enable this tracer, echo in "osnoise" into the current_tracer
+          file.
+
 config MMIOTRACE
 	bool "Memory mapped IO tracing"
 	depends on HAVE_MMIOTRACE_SUPPORT && PCI
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index b28d3e5013cd..b1c47ccf4f73 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -58,6 +58,7 @@ obj-$(CONFIG_IRQSOFF_TRACER) += trace_irqsoff.o
 obj-$(CONFIG_PREEMPT_TRACER) += trace_irqsoff.o
 obj-$(CONFIG_SCHED_TRACER) += trace_sched_wakeup.o
 obj-$(CONFIG_HWLAT_TRACER) += trace_hwlat.o
+obj-$(CONFIG_OSNOISE_TRACER) += trace_osnoise.o
 obj-$(CONFIG_NOP_TRACER) += trace_nop.o
 obj-$(CONFIG_STACK_TRACER) += trace_stack.o
 obj-$(CONFIG_MMIOTRACE) += trace_mmiotrace.o
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 87588d1e24ca..b959c9ec9711 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -44,6 +44,7 @@ enum trace_type {
 	TRACE_BLK,
 	TRACE_BPUTS,
 	TRACE_HWLAT,
+	TRACE_OSNOISE,
 	TRACE_RAW_DATA,
 	TRACE_FUNC_REPEATS,
 
@@ -297,7 +298,8 @@ struct trace_array {
 	struct array_buffer	max_buffer;
 	bool			allocated_snapshot;
 #endif
-#if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)
+#if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER) \
+	|| defined(CONFIG_OSNOISE_TRACER)
 	unsigned long		max_latency;
 #ifdef CONFIG_FSNOTIFY
 	struct dentry		*d_max_latency;
@@ -445,6 +447,7 @@ extern void __ftrace_bad_type(void);
 		IF_ASSIGN(var, ent, struct bprint_entry, TRACE_BPRINT);	\
 		IF_ASSIGN(var, ent, struct bputs_entry, TRACE_BPUTS);	\
 		IF_ASSIGN(var, ent, struct hwlat_entry, TRACE_HWLAT);	\
+		IF_ASSIGN(var, ent, struct osnoise_entry, TRACE_OSNOISE);\
 		IF_ASSIGN(var, ent, struct raw_data_entry, TRACE_RAW_DATA);\
 		IF_ASSIGN(var, ent, struct trace_mmiotrace_rw,		\
 			  TRACE_MMIO_RW);				\
@@ -675,8 +678,8 @@ void update_max_tr_single(struct trace_array *tr,
 			  struct task_struct *tsk, int cpu);
 #endif /* CONFIG_TRACER_MAX_TRACE */
 
-#if (defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)) && \
-	defined(CONFIG_FSNOTIFY)
+#if (defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER) \
+	|| defined(CONFIG_OSNOISE_TRACER)) && defined(CONFIG_FSNOTIFY)
 #define LATENCY_FS_NOTIFY
 #endif
 
diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
index 251c819cf0c5..158c0984b59b 100644
--- a/kernel/trace/trace_entries.h
+++ b/kernel/trace/trace_entries.h
@@ -360,3 +360,28 @@ FTRACE_ENTRY(func_repeats, func_repeats_entry,
 		 __entry->count,
 		 FUNC_REPEATS_GET_DELTA_TS(__entry))
 );
+
+FTRACE_ENTRY(osnoise, osnoise_entry,
+
+	TRACE_OSNOISE,
+
+	F_STRUCT(
+		__field(	u64,			noise		)
+		__field(	u64,			runtime		)
+		__field(	u64,			max_sample	)
+		__field(	unsigned int,		hw_count	)
+		__field(	unsigned int,		nmi_count	)
+		__field(	unsigned int,		irq_count	)
+		__field(	unsigned int,		softirq_count	)
+		__field(	unsigned int,		thread_count	)
+	),
+
+	F_printk("noise:%llu\tmax_sample:%llu\thw:%u\tnmi:%u\tirq:%u\tsoftirq:%u\tthread:%u\n",
+		 __entry->noise,
+		 __entry->max_sample,
+		 __entry->hw_count,
+		 __entry->nmi_count,
+		 __entry->irq_count,
+		 __entry->softirq_count,
+		 __entry->thread_count)
+);
diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
new file mode 100644
index 000000000000..4e2c47dc4f19
--- /dev/null
+++ b/kernel/trace/trace_osnoise.c
@@ -0,0 +1,1384 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * OS Noise Tracer: computes the OS Noise suffered by a running thread.
+ *
+ * Based on "hwlat_detector" tracer by:
+ *   Copyright (C) 2008-2009 Jon Masters, Red Hat, Inc. <jcm@redhat.com>
+ *   Copyright (C) 2013-2016 Steven Rostedt, Red Hat, Inc. <srostedt@redhat.com>
+ *   With feedback from Clark Williams <williams@redhat.com>
+ *
+ * And also based on the rtsl tracer presented on:
+ *  DE OLIVEIRA, Daniel Bristot, et al. Demystifying the real-time linux
+ *  scheduling latency. In: 32nd Euromicro Conference on Real-Time Systems
+ *  (ECRTS 2020). Schloss Dagstuhl-Leibniz-Zentrum fur Informatik, 2020.
+ *
+ * Copyright (C) 2021 Daniel Bristot de Oliveira, Red Hat, Inc. <bristot@redhat.com>
+ */
+
+#include <linux/kthread.h>
+#include <linux/tracefs.h>
+#include <linux/uaccess.h>
+#include <linux/cpumask.h>
+#include <linux/delay.h>
+#include <linux/sched/clock.h>
+#include <linux/sched.h>
+#include "trace.h"
+
+#ifdef CONFIG_X86_LOCAL_APIC
+#include <asm/trace/irq_vectors.h>
+#undef TRACE_INCLUDE_PATH
+#undef TRACE_INCLUDE_FILE
+#endif /* CONFIG_X86_LOCAL_APIC */
+
+#include <trace/events/irq.h>
+#include <trace/events/sched.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/osnoise.h>
+
+static struct trace_array	*osnoise_trace;
+
+/*
+ * Default values.
+ */
+#define BANNER			"osnoise: "
+#define DEFAULT_SAMPLE_PERIOD	1000000			/* 1s */
+#define DEFAULT_SAMPLE_RUNTIME	1000000			/* 1s */
+
+/*
+ * NMI runtime info.
+ */
+struct osn_nmi {
+	u64	count;
+	u64	delta_start;
+};
+
+/*
+ * IRQ runtime info.
+ */
+struct osn_irq {
+	u64	count;
+	u64	arrival_time;
+	u64	delta_start;
+};
+
+/*
+ * sofirq runtime info.
+ */
+struct osn_softirq {
+	u64	count;
+	u64	arrival_time;
+	u64	delta_start;
+};
+
+/*
+ * thread runtime info.
+ */
+struct osn_thread {
+	u64	count;
+	u64	arrival_time;
+	u64	delta_start;
+};
+
+/*
+ * Runtime information: this structure saves the runtime information used by
+ * one sampling thread.
+ */
+struct osnoise_variables {
+	struct task_struct	*kthread;
+	bool			sampling;
+	pid_t			pid;
+	struct osn_nmi		nmi;
+	struct osn_irq		irq;
+	struct osn_softirq	softirq;
+	struct osn_thread	thread;
+	local_t			int_counter;
+};
+
+/*
+ * Per-cpu runtime information.
+ */
+DEFINE_PER_CPU(struct osnoise_variables, per_cpu_osnoise_var);
+
+/*
+ * this_cpu_osn_var - Return the per-cpu osnoise_variables on its relative CPU
+ */
+static inline struct osnoise_variables *this_cpu_osn_var(void)
+{
+	return this_cpu_ptr(&per_cpu_osnoise_var);
+}
+
+/*
+ * osn_var_reset - Reset the values of the given osnoise_variables
+ */
+static inline void osn_var_reset(struct osnoise_variables *osn_var)
+{
+	/*
+	 * So far, all the values are initialized as 0, so
+	 * zeroing the structure is perfect.
+	 */
+	memset(osn_var, 0, sizeof(*osn_var));
+}
+
+/*
+ * osn_var_reset_all - Reset the value of all per-cpu osnoise_variables
+ */
+static inline void osn_var_reset_all(void)
+{
+	struct osnoise_variables *osn_var;
+	int cpu;
+
+	for_each_cpu(cpu, cpu_online_mask) {
+		osn_var = per_cpu_ptr(&per_cpu_osnoise_var, cpu);
+		osn_var_reset(osn_var);
+	}
+}
+
+/*
+ * Tells NMIs to call back to the osnoise tracer to record timestamps.
+ */
+bool trace_osnoise_callback_enabled;
+
+/*
+ * osnoise sample structure definition. Used to store the statistics of a
+ * sample run.
+ */
+struct osnoise_sample {
+	u64			runtime;	/* runtime */
+	u64			noise;		/* noise */
+	u64			max_sample;	/* max single noise sample */
+	int			hw_count;	/* # HW (incl. hypervisor) interference */
+	int			nmi_count;	/* # NMIs during this sample */
+	int			irq_count;	/* # IRQs during this sample */
+	int			softirq_count;	/* # softirqs during this sample */
+	int			thread_count;	/* # threads during this sample */
+};
+
+/*
+ * Protect the interface.
+ */
+struct mutex interface_lock;
+
+/*
+ * Tracer data.
+ */
+static struct osnoise_data {
+	u64	sample_period;		/* total sampling period */
+	u64	sample_runtime;		/* active sampling portion of period */
+	u64	stop_tracing;		/* stop trace in the inside operation (loop) */
+	u64	stop_tracing_total;	/* stop trace in the outside operation (report) */
+	bool	tainted;		/* infor users and developers about a problem */
+} osnoise_data = {
+	.sample_period			= DEFAULT_SAMPLE_PERIOD,
+	.sample_runtime			= DEFAULT_SAMPLE_RUNTIME,
+	.stop_tracing			= 0,
+	.stop_tracing_total		= 0,
+};
+
+/*
+ * Boolean variable used to inform that the tracer is currently sampling.
+ */
+static bool osnoise_busy;
+
+/*
+ * Print the osnoise header info.
+ */
+static void print_osnoise_headers(struct seq_file *s)
+{
+	if (osnoise_data.tainted)
+		seq_puts(s, "# osnoise is tainted!\n");
+
+	seq_puts(s, "#                                _-----=> irqs-off\n");
+	seq_puts(s, "#                               / _----=> need-resched\n");
+	seq_puts(s, "#                              | / _---=> hardirq/softirq\n");
+	seq_puts(s, "#                              || / _--=> preempt-depth     ");
+	seq_puts(s, "                       MAX\n");
+
+	seq_puts(s, "#                              || /                         ");
+	seq_puts(s, "                    SINGLE      Interference counters:\n");
+
+	seq_puts(s, "#                              ||||               RUNTIME   ");
+	seq_puts(s, "   NOISE  %% OF CPU  NOISE    +-----------------------------+\n");
+
+	seq_puts(s, "#           TASK-PID      CPU# ||||   TIMESTAMP    IN US    ");
+	seq_puts(s, "   IN US  AVAILABLE  IN US     HW    NMI    IRQ   SIRQ THREAD\n");
+
+	seq_puts(s, "#              | |         |   ||||      |           |      ");
+	seq_puts(s, "       |    |            |      |      |      |      |      |\n");
+}
+
+/*
+ * osnoise_taint - report an osnoise error.
+ */
+#define osnoise_taint(msg) ({							\
+	struct trace_array *tr = osnoise_trace;					\
+										\
+	trace_array_printk_buf(tr->array_buffer.buffer, _THIS_IP_, msg);	\
+	osnoise_data.tainted = true;						\
+})
+
+/*
+ * Record an osnoise_sample into the tracer buffer.
+ */
+static void trace_osnoise_sample(struct osnoise_sample *sample)
+{
+	struct trace_array *tr = osnoise_trace;
+	struct trace_buffer *buffer = tr->array_buffer.buffer;
+	struct trace_event_call *call = &event_osnoise;
+	struct ring_buffer_event *event;
+	struct osnoise_entry *entry;
+
+	event = trace_buffer_lock_reserve(buffer, TRACE_OSNOISE, sizeof(*entry),
+					  tracing_gen_ctx());
+	if (!event)
+		return;
+	entry	= ring_buffer_event_data(event);
+	entry->runtime		= sample->runtime;
+	entry->noise		= sample->noise;
+	entry->max_sample	= sample->max_sample;
+	entry->hw_count		= sample->hw_count;
+	entry->nmi_count	= sample->nmi_count;
+	entry->irq_count	= sample->irq_count;
+	entry->softirq_count	= sample->softirq_count;
+	entry->thread_count	= sample->thread_count;
+
+	if (!call_filter_check_discard(call, entry, buffer, event))
+		trace_buffer_unlock_commit_nostack(buffer, event);
+}
+
+/*
+ * Macros to encapsulate the time capturing infrastructure.
+ */
+#define time_get()	trace_clock_local()
+#define time_to_us(x)	div_u64(x, 1000)
+#define time_sub(a, b)	((a) - (b))
+
+/*
+ * cond_move_irq_delta_start - Forward the delta_start of a running IRQ
+ *
+ * If an IRQ is preempted by an NMI, its delta_start is pushed forward
+ * to discount the NMI interference.
+ *
+ * See get_int_safe_duration().
+ */
+static inline void
+cond_move_irq_delta_start(struct osnoise_variables *osn_var, u64 duration)
+{
+	if (osn_var->irq.delta_start)
+		osn_var->irq.delta_start += duration;
+}
+
+#ifndef CONFIG_PREEMPT_RT
+/*
+ * cond_move_softirq_delta_start - Forward the delta_start of a running softirq.
+ *
+ * If a softirq is preempted by an IRQ or NMI, its delta_start is pushed
+ * forward to discount the interference.
+ *
+ * See get_int_safe_duration().
+ */
+static inline void
+cond_move_softirq_delta_start(struct osnoise_variables *osn_var, u64 duration)
+{
+	if (osn_var->softirq.delta_start)
+		osn_var->softirq.delta_start += duration;
+}
+#else /* CONFIG_PREEMPT_RT */
+#define cond_move_softirq_delta_start(osn_var, duration) do {} while (0)
+#endif
+
+/*
+ * cond_move_thread_delta_start - Forward the delta_start of a running thread
+ *
+ * If a noisy thread is preempted by an softirq, IRQ or NMI, its delta_start
+ * is pushed forward to discount the interference.
+ *
+ * See get_int_safe_duration().
+ */
+static inline void
+cond_move_thread_delta_start(struct osnoise_variables *osn_var, u64 duration)
+{
+	if (osn_var->thread.delta_start)
+		osn_var->thread.delta_start += duration;
+}
+
+/*
+ * get_int_safe_duration - Get the duration of a window
+ *
+ * The irq, softirq and thread varaibles need to have its duration without
+ * the interference from higher priority interrupts. Instead of keeping a
+ * variable to discount the interrupt interference from these variables, the
+ * starting time of these variables are pushed forward with the interrupt's
+ * duration. In this way, a single variable is used to:
+ *
+ *   - Know if a given window is being measured.
+ *   - Account its duration.
+ *   - Discount the interference.
+ *
+ * To avoid getting inconsistent values, e.g.,:
+ *
+ *	now = time_get()
+ *		--->	interrupt!
+ *			delta_start -= int duration;
+ *		<---
+ *	duration = now - delta_start;
+ *
+ *	result: negative duration if the variable duration before the
+ *	interrupt was smaller than the interrupt execution.
+ *
+ * A counter of interrupts is used. If the counter increased, try
+ * to capture an interference safe duration.
+ */
+static inline s64
+get_int_safe_duration(struct osnoise_variables *osn_var, u64 *delta_start)
+{
+	u64 int_counter, now;
+	s64 duration;
+
+	do {
+		int_counter = local_read(&osn_var->int_counter);
+		/* synchronize with interrupts */
+		barrier();
+
+		now = time_get();
+		duration = (now - *delta_start);
+
+		/* synchronize with interrupts */
+		barrier();
+	} while (int_counter != local_read(&osn_var->int_counter));
+
+	/*
+	 * This is an evidence of race conditions that cause
+	 * a value to be "discounted" too much.
+	 */
+	if (duration < 0)
+		osnoise_taint("Negative duration!\n");
+
+	*delta_start = 0;
+
+	return duration;
+}
+
+/*
+ *
+ * set_int_safe_time - Save the current time on *time, aware of interference
+ *
+ * Get the time, taking into consideration a possible interference from
+ * higher priority interrupts.
+ *
+ * See get_int_safe_duration() for an explanation.
+ */
+static u64
+set_int_safe_time(struct osnoise_variables *osn_var, u64 *time)
+{
+	u64 int_counter;
+
+	do {
+		int_counter = local_read(&osn_var->int_counter);
+		/* synchronize with interrupts */
+		barrier();
+
+		*time = time_get();
+
+		/* synchronize with interrupts */
+		barrier();
+	} while (int_counter != local_read(&osn_var->int_counter));
+
+	return int_counter;
+}
+
+/*
+ * trace_osnoise_callback - NMI entry/exit callback
+ *
+ * This function is called at the entry and exit NMI code. The bool enter
+ * distinguishes between either case. This function is used to note a NMI
+ * occurrence, compute the noise caused by the NMI, and to remove the noise
+ * it is potentially causing on other interference variables.
+ */
+void trace_osnoise_callback(bool enter)
+{
+	struct osnoise_variables *osn_var = this_cpu_osn_var();
+	u64 duration;
+
+	if (!osn_var->sampling)
+		return;
+
+	/*
+	 * Currently trace_clock_local() calls sched_clock() and the
+	 * generic version is not NMI safe.
+	 */
+	if (!IS_ENABLED(CONFIG_GENERIC_SCHED_CLOCK)) {
+		if (enter) {
+			osn_var->nmi.delta_start = time_get();
+			local_inc(&osn_var->int_counter);
+		} else {
+			duration = time_get() - osn_var->nmi.delta_start;
+
+			trace_nmi_noise(osn_var->nmi.delta_start, duration);
+
+			cond_move_irq_delta_start(osn_var, duration);
+			cond_move_softirq_delta_start(osn_var, duration);
+			cond_move_thread_delta_start(osn_var, duration);
+		}
+	}
+
+	if (enter)
+		osn_var->nmi.count++;
+}
+
+/*
+ * osnoise_trace_irq_entry - Note the starting of an IRQ
+ *
+ * Save the starting time of an IRQ. As IRQs are non-preemptive to other IRQs,
+ * it is safe to use a single variable (ons_var->irq) to save the statistics.
+ * The arrival_time is used to report... the arrival time. The delta_start
+ * is used to compute the duration at the IRQ exit handler. See
+ * cond_move_irq_delta_start().
+ */
+void osnoise_trace_irq_entry(int id)
+{
+	struct osnoise_variables *osn_var = this_cpu_osn_var();
+
+	if (!osn_var->sampling)
+		return;
+	/*
+	 * This value will be used in the report, but not to compute
+	 * the execution time, so it is safe to get it unsafe.
+	 */
+	osn_var->irq.arrival_time = time_get();
+	set_int_safe_time(osn_var, &osn_var->irq.delta_start);
+	osn_var->irq.count++;
+
+	local_inc(&osn_var->int_counter);
+}
+
+/*
+ * osnoise_irq_exit - Note the end of an IRQ, sava data and trace
+ *
+ * Computes the duration of the IRQ noise, and trace it. Also discounts the
+ * interference from other sources of noise could be currently being accounted.
+ */
+void osnoise_trace_irq_exit(int id, const char *desc)
+{
+	struct osnoise_variables *osn_var = this_cpu_osn_var();
+	int duration;
+
+	if (!osn_var->sampling)
+		return;
+
+	duration = get_int_safe_duration(osn_var, &osn_var->irq.delta_start);
+	trace_irq_noise(id, desc, osn_var->irq.arrival_time, duration);
+	osn_var->irq.arrival_time = 0;
+	cond_move_softirq_delta_start(osn_var, duration);
+	cond_move_thread_delta_start(osn_var, duration);
+}
+
+/*
+ * trace_irqentry_callback - Callback to the irq:irq_entry traceevent
+ *
+ * Used to note the starting of an IRQ occurece.
+ */
+static void trace_irqentry_callback(void *data, int irq,
+				    struct irqaction *action)
+{
+	osnoise_trace_irq_entry(irq);
+}
+
+/*
+ * trace_irqexit_callback - Callback to the irq:irq_exit traceevent
+ *
+ * Used to note the end of an IRQ occurece.
+ */
+static void trace_irqexit_callback(void *data, int irq,
+				   struct irqaction *action, int ret)
+{
+	osnoise_trace_irq_exit(irq, action->name);
+}
+
+/*
+ * arch specific register function.
+ */
+int __weak osnoise_arch_register(void)
+{
+	return 0;
+}
+
+/*
+ * arch specific unregister function.
+ */
+void __weak osnoise_arch_unregister(void)
+{
+	return;
+}
+
+/*
+ * hook_irq_events - Hook IRQ handling events
+ *
+ * This function hooks the IRQ related callbacks to the respective trace
+ * events.
+ */
+int hook_irq_events(void)
+{
+	int ret;
+
+	ret = register_trace_irq_handler_entry(trace_irqentry_callback, NULL);
+	if (ret)
+		goto out_err;
+
+	ret = register_trace_irq_handler_exit(trace_irqexit_callback, NULL);
+	if (ret)
+		goto out_unregister_entry;
+
+	ret = osnoise_arch_register();
+	if (ret)
+		goto out_irq_exit;
+
+	return 0;
+
+out_irq_exit:
+	unregister_trace_irq_handler_exit(trace_irqexit_callback, NULL);
+out_unregister_entry:
+	unregister_trace_irq_handler_entry(trace_irqentry_callback, NULL);
+out_err:
+	return -EINVAL;
+}
+
+/*
+ * unhook_irq_events - Unhook IRQ handling events
+ *
+ * This function unhooks the IRQ related callbacks to the respective trace
+ * events.
+ */
+void unhook_irq_events(void)
+{
+	osnoise_arch_unregister();
+	unregister_trace_irq_handler_exit(trace_irqexit_callback, NULL);
+	unregister_trace_irq_handler_entry(trace_irqentry_callback, NULL);
+}
+
+#ifndef CONFIG_PREEMPT_RT
+/*
+ * trace_softirq_entry_callback - Note the starting of a softirq
+ *
+ * Save the starting time of a softirq. As softirqs are non-preemptive to
+ * other softirqs, it is safe to use a single variable (ons_var->softirq)
+ * to save the statistics. The arrival_time is used to report... the
+ * arrival time. The delta_start is used to compute the duration at the
+ * softirq exit handler. See cond_move_softirq_delta_start().
+ */
+void trace_softirq_entry_callback(void *data, unsigned int vec_nr)
+{
+	struct osnoise_variables *osn_var = this_cpu_osn_var();
+
+	if (!osn_var->sampling)
+		return;
+	/*
+	 * This value will be used in the report, but not to compute
+	 * the execution time, so it is safe to get it unsafe.
+	 */
+	osn_var->softirq.arrival_time = time_get();
+	set_int_safe_time(osn_var, &osn_var->softirq.delta_start);
+	osn_var->softirq.count++;
+
+	local_inc(&osn_var->int_counter);
+}
+
+/*
+ * trace_softirq_exit_callback - Note the end of an softirq
+ *
+ * Computes the duration of the softirq noise, and trace it. Also discounts the
+ * interference from other sources of noise could be currently being accounted.
+ */
+void trace_softirq_exit_callback(void *data, unsigned int vec_nr)
+{
+	struct osnoise_variables *osn_var = this_cpu_osn_var();
+	int duration;
+
+	if (!osn_var->sampling)
+		return;
+
+	duration = get_int_safe_duration(osn_var, &osn_var->softirq.delta_start);
+	trace_softirq_noise(vec_nr, osn_var->softirq.arrival_time, duration);
+	cond_move_thread_delta_start(osn_var, duration);
+	osn_var->softirq.arrival_time = 0;
+}
+
+/*
+ * hook_softirq_events - Hook softirq handling events
+ *
+ * This function hooks the softirq related callbacks to the respective trace
+ * events.
+ */
+static int hook_softirq_events(void)
+{
+	int ret;
+
+	ret = register_trace_softirq_entry(trace_softirq_entry_callback, NULL);
+	if (ret)
+		goto out_err;
+
+	ret = register_trace_softirq_exit(trace_softirq_exit_callback, NULL);
+	if (ret)
+		goto out_unreg_entry;
+
+	return 0;
+
+out_unreg_entry:
+	unregister_trace_softirq_entry(trace_softirq_entry_callback, NULL);
+out_err:
+	return -EINVAL;
+}
+
+/*
+ * unhook_softirq_events - Unhook softirq handling events
+ *
+ * This function hooks the softirq related callbacks to the respective trace
+ * events.
+ */
+static void unhook_softirq_events(void)
+{
+	unregister_trace_softirq_entry(trace_softirq_entry_callback, NULL);
+	unregister_trace_softirq_exit(trace_softirq_exit_callback, NULL);
+}
+#else /* CONFIG_PREEMPT_RT */
+/*
+ * softirq are threads on the PREEMPT_RT mode.
+ */
+static int hook_softirq_events(void)
+{
+	return 0;
+}
+static void unhook_softirq_events(void)
+{
+}
+#endif
+
+/*
+ * thread_entry - Record the starting of a thread noise window
+ *
+ * It saves the context switch time for a noisy thread, and increments
+ * the interference counters.
+ */
+static void
+thread_entry(struct osnoise_variables *osn_var, struct task_struct *t)
+{
+	if (!osn_var->sampling)
+		return;
+	/*
+	 * The arrival time will be used in the report, but not to compute
+	 * the execution time, so it is safe to get it unsafe.
+	 */
+	osn_var->thread.arrival_time = time_get();
+
+	set_int_safe_time(osn_var, &osn_var->thread.delta_start);
+
+	osn_var->thread.count++;
+	local_inc(&osn_var->int_counter);
+}
+
+/*
+ * thread_exit - Report the end of a thread noise window
+ *
+ * It computes the total noise from a thread, tracing if needed.
+ */
+static void
+thread_exit(struct osnoise_variables *osn_var, struct task_struct *t)
+{
+	int duration;
+
+	if (!osn_var->sampling)
+		return;
+
+	duration = get_int_safe_duration(osn_var, &osn_var->thread.delta_start);
+
+	trace_thread_noise(t, osn_var->thread.arrival_time, duration);
+
+	osn_var->thread.arrival_time = 0;
+}
+
+/*
+ * trace_sched_switch - sched:sched_switch trace event handler
+ *
+ * This function is hooked to the sched:sched_switch trace event, and it is
+ * used to record the beginning and to report the end of a thread noise window.
+ */
+void
+trace_sched_switch_callback(void *data, bool preempt, struct task_struct *p,
+			    struct task_struct *n)
+{
+	struct osnoise_variables *osn_var = this_cpu_osn_var();
+
+	if (p->pid != osn_var->pid)
+		thread_exit(osn_var, p);
+
+	if (n->pid != osn_var->pid)
+		thread_entry(osn_var, n);
+}
+
+/*
+ * hook_thread_events - Hook the insturmentation for thread noise
+ *
+ * Hook the osnoise tracer callbacks to handle the noise from other
+ * threads on the necessary kernel events.
+ */
+int hook_thread_events(void)
+{
+	int ret;
+
+	ret = register_trace_sched_switch(trace_sched_switch_callback, NULL);
+	if (ret)
+		return -EINVAL;
+
+	return 0;
+}
+
+/*
+ * unhook_thread_events - *nhook the insturmentation for thread noise
+ *
+ * Unook the osnoise tracer callbacks to handle the noise from other
+ * threads on the necessary kernel events.
+ */
+void unhook_thread_events(void)
+{
+	unregister_trace_sched_switch(trace_sched_switch_callback, NULL);
+}
+
+/*
+ * save_osn_sample_stats - Save the osnoise_sample statistics
+ *
+ * Save the osnoise_sample statistics before the sampling phase. These
+ * values will be used later to compute the diff betwneen the statistics
+ * before and after the osnoise sampling.
+ */
+void save_osn_sample_stats(struct osnoise_variables *osn_var, struct osnoise_sample *s)
+{
+	s->nmi_count = osn_var->nmi.count;
+	s->irq_count = osn_var->irq.count;
+	s->softirq_count = osn_var->softirq.count;
+	s->thread_count = osn_var->thread.count;
+}
+
+/*
+ * diff_osn_sample_stats - Compute the osnoise_sample statistics
+ *
+ * After a sample period, compute the difference on the osnoise_sample
+ * statistics. The struct osnoise_sample *s contains the statistics saved via
+ * save_osn_sample_stats() before the osnoise sampling.
+ */
+void diff_osn_sample_stats(struct osnoise_variables *osn_var, struct osnoise_sample *s)
+{
+	s->nmi_count = osn_var->nmi.count - s->nmi_count;
+	s->irq_count = osn_var->irq.count - s->irq_count;
+	s->softirq_count = osn_var->softirq.count - s->softirq_count;
+	s->thread_count = osn_var->thread.count - s->thread_count;
+}
+
+/*
+ * osnoise_stop_tracing - Stop tracing and the tracer.
+ */
+static void osnoise_stop_tracing(void)
+{
+	struct trace_array *tr = osnoise_trace;
+	tracer_tracing_off(tr);
+}
+
+/*
+ * run_osnoise - Sample the time and look for osnoise
+ *
+ * Used to capture the time, looking for potential osnoise latency repeatedly.
+ * Different from hwlat_detector, it is called with preemption and interrupts
+ * enabled. This allows irqs, softirqs and threads to run, interfering on the
+ * osnoise sampling thread, as they would do with a regular thread.
+ */
+static int run_osnoise(void)
+{
+	struct osnoise_variables *osn_var = this_cpu_osn_var();
+	u64 noise = 0, sum_noise = 0, max_noise = 0;
+	struct trace_array *tr = osnoise_trace;
+	u64 start, sample, last_sample;
+	u64 last_int_count, int_count;
+	s64 total, last_total = 0;
+	struct osnoise_sample s;
+	unsigned int threshold;
+	int hw_count = 0;
+	u64 runtime, stop_in;
+	int ret = -1;
+
+	/*
+	 * Considers the current thread as the workload.
+	 */
+	osn_var->pid = current->pid;
+
+	/*
+	 * Save the current stats for the diff
+	 */
+	save_osn_sample_stats(osn_var, &s);
+
+	/*
+	 * if threshold is 0, use the default value of 5 us.
+	 */
+	threshold = tracing_thresh ? : 5000;
+
+	/*
+	 * Make sure NMIs see sampling first
+	 */
+	osn_var->sampling = true;
+	barrier();
+
+	/*
+	 * Transform the *_us config to nanoseconds to avoid the
+	 * division on the main loop.
+	 */
+	runtime = osnoise_data.sample_runtime * NSEC_PER_USEC;
+	stop_in = osnoise_data.stop_tracing * NSEC_PER_USEC;
+
+	/*
+	 * Start timestemp
+	 */
+	start = time_get();
+
+	/*
+	 * "previous" loop.
+	 */
+	last_int_count = set_int_safe_time(osn_var, &last_sample);
+
+	do {
+		/*
+		 * Get sample!
+		 */
+		int_count = set_int_safe_time(osn_var, &sample);
+
+		noise = time_sub(sample, last_sample);
+
+		/*
+		 * This shouldn't happen.
+		 */
+		if (noise < 0) {
+			osnoise_taint("negative noise!");
+			goto out;
+		}
+
+		/*
+		 * Sample runtime.
+		 */
+		total = time_sub(sample, start);
+
+		/*
+		 * Check for possible overflows.
+		 */
+		if (total < last_total) {
+			osnoise_taint("total overflow!");
+			break;
+		}
+
+		last_total = total;
+
+		if (noise >= threshold) {
+			int interference = int_count - last_int_count;
+
+			if (noise > max_noise)
+				max_noise = noise;
+
+			if (!interference)
+				hw_count++;
+
+			sum_noise += noise;
+
+			trace_sample_threshold(last_sample, noise, interference);
+
+			if (osnoise_data.stop_tracing)
+				if (noise > stop_in)
+					osnoise_stop_tracing();
+		}
+
+		/*
+		 * For the non-preemptive kernel config: let threads runs, if
+		 * they so wish.
+		 */
+		cond_resched();
+
+		last_sample = sample;
+		last_int_count = int_count;
+
+	} while (total < runtime && !kthread_should_stop());
+
+	/*
+	 * Finish the above in the view for interrupts.
+	 */
+	barrier();
+
+	osn_var->sampling = false;
+
+	/*
+	 * Make sure sampling data is no longer updated.
+	 */
+	barrier();
+
+	/*
+	 * Save noise info.
+	 */
+	s.noise = time_to_us(sum_noise);
+	s.runtime = time_to_us(total);
+	s.max_sample = time_to_us(max_noise);
+	s.hw_count = hw_count;
+
+	/* Save interference stats info */
+	diff_osn_sample_stats(osn_var, &s);
+
+	trace_osnoise_sample(&s);
+
+	/* Keep a running maximum ever recorded osnoise "latency" */
+	if (max_noise > tr->max_latency) {
+		tr->max_latency = max_noise;
+		latency_fsnotify(tr);
+	}
+
+	if (osnoise_data.stop_tracing_total)
+		if (s.noise > osnoise_data.stop_tracing_total)
+			osnoise_stop_tracing();
+
+	return 0;
+out:
+	return ret;
+}
+
+static struct cpumask osnoise_cpumask;
+static struct cpumask save_cpumask;
+
+/*
+ * osnoise_main - The osnoise detection kernel thread
+ *
+ * Calls run_osnoise() function to measure the osnoise for the configured runtime,
+ * every period.
+ */
+static int osnoise_main(void *data)
+{
+	s64 interval;
+
+	while (!kthread_should_stop()) {
+
+		run_osnoise();
+
+		mutex_lock(&interface_lock);
+		interval = osnoise_data.sample_period - osnoise_data.sample_runtime;
+		mutex_unlock(&interface_lock);
+
+		do_div(interval, USEC_PER_MSEC);
+
+		/*
+		 * differently from hwlat_detector, the osnoise tracer can run
+		 * without a pause because preemption is on.
+		 */
+		if (interval < 1)
+			continue;
+
+		if (msleep_interruptible(interval))
+			break;
+	}
+
+	return 0;
+}
+
+/*
+ * stop_per_cpu_kthread - stop per-cpu threads
+ *
+ * Stop the osnoise sampling htread. Use this on unload and at system
+ * shutdown.
+ */
+static void stop_per_cpu_kthreads(void)
+{
+	struct task_struct *kthread;
+	int cpu;
+
+	for_each_online_cpu(cpu) {
+		kthread = per_cpu(per_cpu_osnoise_var, cpu).kthread;
+		if (kthread)
+			kthread_stop(kthread);
+		per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;
+	}
+}
+
+/*
+ * start_per_cpu_kthread - Kick off per-cpu osnoise sampling kthreads
+ *
+ * This starts the kernel thread that will look for osnoise on many
+ * cpus.
+ */
+static int start_per_cpu_kthreads(struct trace_array *tr)
+{
+	struct cpumask *current_mask = &save_cpumask;
+	struct task_struct *kthread;
+	char comm[24];
+	int cpu;
+
+	get_online_cpus();
+	/*
+	 * Run only on CPUs in which trace and osnoise are allowed to run.
+	 */
+	cpumask_and(current_mask, tr->tracing_cpumask, &osnoise_cpumask);
+	/*
+	 * And the CPU is online.
+	 */
+	cpumask_and(current_mask, cpu_online_mask, current_mask);
+	put_online_cpus();
+
+	for_each_online_cpu(cpu)
+		per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;
+
+	for_each_cpu(cpu, current_mask) {
+		snprintf(comm, 24, "osnoise/%d", cpu);
+
+		kthread = kthread_create_on_cpu(osnoise_main, NULL, cpu, comm);
+
+		if (IS_ERR(kthread)) {
+			pr_err(BANNER "could not start sampling thread\n");
+			stop_per_cpu_kthreads();
+			return -ENOMEM;
+		}
+
+		per_cpu(per_cpu_osnoise_var, cpu).kthread = kthread;
+		wake_up_process(kthread);
+	}
+
+	return 0;
+}
+
+/*
+ * osnoise_cpus_read - Read function for reading the "cpus" file
+ * @filp: The active open file structure
+ * @ubuf: The userspace provided buffer to read value into
+ * @cnt: The maximum number of bytes to read
+ * @ppos: The current "file" position
+ *
+ * Prints the "cpus" output into the user-provided buffer.
+ */
+static ssize_t
+osnoise_cpus_read(struct file *filp, char __user *ubuf, size_t count,
+		  loff_t *ppos)
+{
+	char *mask_str;
+	int len;
+
+	mutex_lock(&interface_lock);
+
+	len = snprintf(NULL, 0, "%*pbl\n", cpumask_pr_args(&osnoise_cpumask)) + 1;
+	mask_str = kmalloc(len, GFP_KERNEL);
+	if (!mask_str) {
+		count = -ENOMEM;
+		goto out_unlock;
+	}
+
+	len = snprintf(mask_str, len, "%*pbl\n", cpumask_pr_args(&osnoise_cpumask));
+	if (len >= count) {
+		count = -EINVAL;
+		goto out_free;
+	}
+
+	count = simple_read_from_buffer(ubuf, count, ppos, mask_str, len);
+
+out_free:
+	kfree(mask_str);
+out_unlock:
+	mutex_unlock(&interface_lock);
+
+	return count;
+}
+
+static void osnoise_tracer_start(struct trace_array *tr);
+static void osnoise_tracer_stop(struct trace_array *tr);
+
+/*
+ * osnoise_cpus_write - Write function for "cpus" 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
+ *
+ * This function provides a write implementation for the "cpus"
+ * interface to the osnoise trace. By default, it lists all  CPUs,
+ * in this way, allowing osnoise threads to run on any online CPU
+ * of the system. It serves to restrict the execution of osnoise to the
+ * set of CPUs writing via this interface. Note that osnoise also
+ * respects the "tracing_cpumask." Hence, osnoise threads will run only
+ * on the set of CPUs allowed here AND on "tracing_cpumask." Why not
+ * have just "tracing_cpumask?" Because the user might be interested
+ * in tracing what is running on other CPUs. For instance, one might
+ * run osnoise in one HT CPU while observing what is running on the
+ * sibling HT CPU.
+ */
+static ssize_t
+osnoise_cpus_write(struct file *filp, const char __user *ubuf, size_t count,
+		   loff_t *ppos)
+{
+	struct trace_array *tr = osnoise_trace;
+	cpumask_var_t osnoise_cpumask_new;
+	int running, err;
+	char buf[256];
+
+	if (count >= 256)
+		return -EINVAL;
+
+	if (copy_from_user(buf, ubuf, count))
+		return -EFAULT;
+
+	if (!zalloc_cpumask_var(&osnoise_cpumask_new, GFP_KERNEL))
+		return -ENOMEM;
+
+	err = cpulist_parse(buf, osnoise_cpumask_new);
+	if (err)
+		goto err_free;
+
+	/*
+	 * trace_types_lock is taken to avoid concurrency on start/stop
+	 * and osnoise_busy.
+	 */
+	mutex_lock(&trace_types_lock);
+	running = osnoise_busy;
+	if (running)
+		osnoise_tracer_stop(tr);
+
+	mutex_lock(&interface_lock);
+	cpumask_copy(&osnoise_cpumask, osnoise_cpumask_new);
+	mutex_unlock(&interface_lock);
+
+	if (running)
+		osnoise_tracer_start(tr);
+	mutex_unlock(&trace_types_lock);
+
+	free_cpumask_var(osnoise_cpumask_new);
+	return count;
+
+err_free:
+	free_cpumask_var(osnoise_cpumask_new);
+
+	return err;
+}
+
+/*
+ * osnoise/runtime_us: cannot be greater than the period.
+ */
+static struct trace_min_max_param osnoise_runtime = {
+	.lock	= &interface_lock,
+	.val	= &osnoise_data.sample_runtime,
+	.max	= &osnoise_data.sample_period,
+	.min	= NULL,
+};
+
+/*
+ * osnoise/period_us: cannot be smaller than the runtime.
+ */
+static struct trace_min_max_param osnoise_period = {
+	.lock	= &interface_lock,
+	.val	= &osnoise_data.sample_period,
+	.max	= NULL,
+	.min	= &osnoise_data.sample_runtime,
+};
+
+/*
+ * osnoise/stop_tracing_us: no limit.
+ */
+static struct trace_min_max_param osnoise_stop_tracing_in = {
+	.lock	= &interface_lock,
+	.val	= &osnoise_data.stop_tracing,
+	.max	= NULL,
+	.min	= NULL,
+};
+
+/*
+ * osnoise/stop_tracing_total_us: no limit.
+ */
+static struct trace_min_max_param osnoise_stop_tracing_total = {
+	.lock	= &interface_lock,
+	.val	= &osnoise_data.stop_tracing_total,
+	.max	= NULL,
+	.min	= NULL,
+};
+
+static const struct file_operations cpus_fops = {
+	.open		= tracing_open_generic,
+	.read		= osnoise_cpus_read,
+	.write		= osnoise_cpus_write,
+	.llseek		= generic_file_llseek,
+};
+
+/*
+ * init_tracefs - A function to initialize the tracefs interface files
+ *
+ * This function creates entries in tracefs for "osnoise". It creates the
+ * "osnoise" directory in the tracing directory, and within that
+ * directory is the count, runtime and period files to change and view
+ * those values.
+ */
+static int init_tracefs(void)
+{
+	struct dentry *top_dir;
+	struct dentry *tmp;
+	int ret;
+
+	ret = tracing_init_dentry();
+	if (ret)
+		return -ENOMEM;
+
+	top_dir = tracefs_create_dir("osnoise", NULL);
+	if (!top_dir)
+		return -ENOMEM;
+
+	tmp = tracefs_create_file("period_us", 0640, top_dir,
+				  &osnoise_period, &trace_min_max_fops);
+	if (!tmp)
+		goto err;
+
+	tmp = tracefs_create_file("runtime_us", 0644, top_dir,
+				  &osnoise_runtime, &trace_min_max_fops);
+	if (!tmp)
+		goto err;
+
+	tmp = tracefs_create_file("stop_tracing_us", 0640, top_dir,
+				  &osnoise_stop_tracing_in, &trace_min_max_fops);
+	if (!tmp)
+		goto err;
+
+	tmp = tracefs_create_file("stop_tracing_total_us", 0640, top_dir,
+				  &osnoise_stop_tracing_total, &trace_min_max_fops);
+	if (!tmp)
+		goto err;
+
+	tmp = trace_create_file("cpus", 0644, top_dir, NULL, &cpus_fops);
+	if (!tmp)
+		goto err;
+
+	return 0;
+
+err:
+	tracefs_remove(top_dir);
+	return -ENOMEM;
+}
+
+static int osnoise_hook_events(void)
+{
+	int retval;
+
+	/*
+	 * Trace is already hooked, we are re-enabling from
+	 * a stop_tracing_*.
+	 */
+	if (trace_osnoise_callback_enabled)
+		return 0;
+
+	retval = hook_irq_events();
+	if (retval)
+		return -EINVAL;
+
+	retval = hook_softirq_events();
+	if (retval)
+		goto out_unhook_irq;
+
+	retval = hook_thread_events();
+	/*
+	 * All fine!
+	 */
+	if (!retval)
+		return 0;
+
+	unhook_softirq_events();
+out_unhook_irq:
+	unhook_irq_events();
+	return -EINVAL;
+}
+
+static void osnoise_tracer_start(struct trace_array *tr)
+{
+	int retval;
+
+	if (osnoise_busy)
+		return;
+
+	osn_var_reset_all();
+
+	retval = osnoise_hook_events();
+	if (retval)
+		goto out_err;
+	/*
+	 * Make sure NMIs see reseted values.
+	 */
+	barrier();
+	trace_osnoise_callback_enabled = true;
+
+	retval = start_per_cpu_kthreads(tr);
+	/*
+	 * all fine!
+	 */
+	if (!retval)
+		return;
+
+out_err:
+	unhook_irq_events();
+	pr_err(BANNER "Error starting osnoise tracer\n");
+}
+
+static void osnoise_tracer_stop(struct trace_array *tr)
+{
+	if (!osnoise_busy)
+		return;
+
+	trace_osnoise_callback_enabled = false;
+	barrier();
+
+	stop_per_cpu_kthreads();
+
+	unhook_irq_events();
+	unhook_softirq_events();
+	unhook_thread_events();
+
+	osnoise_busy = false;
+}
+
+static int osnoise_tracer_init(struct trace_array *tr)
+{
+	/* Only allow one instance to enable this */
+	if (osnoise_busy)
+		return -EBUSY;
+
+	osnoise_trace = tr;
+
+	tr->max_latency = 0;
+
+	osnoise_tracer_start(tr);
+
+	osnoise_busy = true;
+
+	return 0;
+}
+
+static void osnoise_tracer_reset(struct trace_array *tr)
+{
+	osnoise_tracer_stop(tr);
+}
+
+static struct tracer osnoise_tracer __read_mostly = {
+	.name		= "osnoise",
+	.init		= osnoise_tracer_init,
+	.reset		= osnoise_tracer_reset,
+	.start		= osnoise_tracer_start,
+	.stop		= osnoise_tracer_stop,
+	.print_header	= print_osnoise_headers,
+	.allow_instances = true,
+};
+
+__init static int init_osnoise_tracer(void)
+{
+	int ret;
+
+	mutex_init(&interface_lock);
+
+	cpumask_copy(&osnoise_cpumask, cpu_all_mask);
+
+	ret = register_tracer(&osnoise_tracer);
+	if (ret)
+		return ret;
+
+	init_tracefs();
+
+	return 0;
+}
+late_initcall(init_osnoise_tracer);
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index d0368a569bfa..642b6584eba5 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -1202,7 +1202,6 @@ trace_hwlat_print(struct trace_iterator *iter, int flags,
 	return trace_handle_return(s);
 }
 
-
 static enum print_line_t
 trace_hwlat_raw(struct trace_iterator *iter, int flags,
 		struct trace_event *event)
@@ -1232,6 +1231,76 @@ static struct trace_event trace_hwlat_event = {
 	.funcs		= &trace_hwlat_funcs,
 };
 
+/* TRACE_OSNOISE */
+static enum print_line_t
+trace_osnoise_print(struct trace_iterator *iter, int flags,
+		    struct trace_event *event)
+{
+	struct trace_entry *entry = iter->ent;
+	struct trace_seq *s = &iter->seq;
+	struct osnoise_entry *field;
+	u64 ratio, ratio_dec;
+	u64 net_runtime;
+
+	trace_assign_type(field, entry);
+
+	/*
+	 * compute the available % of cpu time.
+	 */
+	net_runtime = field->runtime - field->noise;
+	ratio = net_runtime * 10000000;
+	do_div(ratio, field->runtime);
+	ratio_dec = do_div(ratio, 100000);
+
+	trace_seq_printf(s, "%llu %10llu %3llu.%05llu %7llu",
+			 field->runtime,
+			 field->noise,
+			 ratio, ratio_dec,
+			 field->max_sample);
+
+	trace_seq_printf(s, " %6u", field->hw_count);
+	trace_seq_printf(s, " %6u", field->nmi_count);
+	trace_seq_printf(s, " %6u", field->irq_count);
+	trace_seq_printf(s, " %6u", field->softirq_count);
+	trace_seq_printf(s, " %6u", field->thread_count);
+
+	trace_seq_putc(s, '\n');
+
+	return trace_handle_return(s);
+}
+
+static enum print_line_t
+trace_osnoise_raw(struct trace_iterator *iter, int flags,
+		  struct trace_event *event)
+{
+	struct osnoise_entry *field;
+	struct trace_seq *s = &iter->seq;
+
+	trace_assign_type(field, iter->ent);
+
+	trace_seq_printf(s, "%lld %llu %llu %u %u %u %u %u\n",
+			 field->runtime,
+			 field->noise,
+			 field->max_sample,
+			 field->hw_count,
+			 field->nmi_count,
+			 field->irq_count,
+			 field->softirq_count,
+			 field->thread_count);
+
+	return trace_handle_return(s);
+}
+
+static struct trace_event_functions trace_osnoise_funcs = {
+	.trace		= trace_osnoise_print,
+	.raw		= trace_osnoise_raw,
+};
+
+static struct trace_event trace_osnoise_event = {
+	.type		= TRACE_OSNOISE,
+	.funcs		= &trace_osnoise_funcs,
+};
+
 /* TRACE_BPUTS */
 static enum print_line_t
 trace_bputs_print(struct trace_iterator *iter, int flags,
@@ -1442,6 +1511,7 @@ static struct trace_event *events[] __initdata = {
 	&trace_bprint_event,
 	&trace_print_event,
 	&trace_hwlat_event,
+	&trace_osnoise_event,
 	&trace_raw_data_event,
 	&trace_func_repeats_event,
 	NULL
-- 
2.30.2

[for-next][PATCH 21/24] trace: Add timerlat tracer

[Steven Rostedt]

From: Daniel Bristot de Oliveira <bristot@redhat.com>

The timerlat tracer aims to help the preemptive kernel developers to
found souces of wakeup latencies of real-time threads. Like cyclictest,
the tracer sets a periodic timer that wakes up a thread. The thread then
computes a *wakeup latency* value as the difference between the *current
time* and the *absolute time* that the timer was set to expire. The main
goal of timerlat is tracing in such a way to help kernel developers.

Usage

Write the ASCII text "timerlat" into the current_tracer file of the
tracing system (generally mounted at /sys/kernel/tracing).

For example:

        [root@f32 ~]# cd /sys/kernel/tracing/
        [root@f32 tracing]# echo timerlat > current_tracer

It is possible to follow the trace by reading the trace trace file:

  [root@f32 tracing]# cat trace
  # tracer: timerlat
  #
  #                              _-----=> irqs-off
  #                             / _----=> need-resched
  #                            | / _---=> hardirq/softirq
  #                            || / _--=> preempt-depth
  #                            || /
  #                            ||||             ACTIVATION
  #         TASK-PID      CPU# ||||   TIMESTAMP    ID            CONTEXT                LATENCY
  #            | |         |   ||||      |         |                  |                       |
          <idle>-0       [000] d.h1    54.029328: #1     context    irq timer_latency       932 ns
           <...>-867     [000] ....    54.029339: #1     context thread timer_latency     11700 ns
          <idle>-0       [001] dNh1    54.029346: #1     context    irq timer_latency      2833 ns
           <...>-868     [001] ....    54.029353: #1     context thread timer_latency      9820 ns
          <idle>-0       [000] d.h1    54.030328: #2     context    irq timer_latency       769 ns
           <...>-867     [000] ....    54.030330: #2     context thread timer_latency      3070 ns
          <idle>-0       [001] d.h1    54.030344: #2     context    irq timer_latency       935 ns
           <...>-868     [001] ....    54.030347: #2     context thread timer_latency      4351 ns

The tracer creates a per-cpu kernel thread with real-time priority that
prints two lines at every activation. The first is the *timer latency*
observed at the *hardirq* context before the activation of the thread.
The second is the *timer latency* observed by the thread, which is the
same level that cyclictest reports. The ACTIVATION ID field
serves to relate the *irq* execution to its respective *thread* execution.

The irq/thread splitting is important to clarify at which context
the unexpected high value is coming from. The *irq* context can be
delayed by hardware related actions, such as SMIs, NMIs, IRQs
or by a thread masking interrupts. Once the timer happens, the delay
can also be influenced by blocking caused by threads. For example, by
postponing the scheduler execution via preempt_disable(),  by the
scheduler execution, or by masking interrupts. Threads can
also be delayed by the interference from other threads and IRQs.

The timerlat can also take advantage of the osnoise: traceevents.
For example:

        [root@f32 ~]# cd /sys/kernel/tracing/
        [root@f32 tracing]# echo timerlat > current_tracer
        [root@f32 tracing]# echo osnoise > set_event
        [root@f32 tracing]# echo 25 > osnoise/stop_tracing_total_us
        [root@f32 tracing]# tail -10 trace
             cc1-87882   [005] d..h...   548.771078: #402268 context    irq timer_latency      1585 ns
             cc1-87882   [005] dNLh1..   548.771082: irq_noise: local_timer:236 start 548.771077442 duration 4597 ns
             cc1-87882   [005] dNLh2..   548.771083: irq_noise: reschedule:253 start 548.771083017 duration 56 ns
             cc1-87882   [005] dNLh2..   548.771086: irq_noise: call_function_single:251 start 548.771083811 duration 2048 ns
             cc1-87882   [005] dNLh2..   548.771088: irq_noise: call_function_single:251 start 548.771086814 duration 1495 ns
             cc1-87882   [005] dNLh2..   548.771091: irq_noise: call_function_single:251 start 548.771089194 duration 1558 ns
             cc1-87882   [005] dNLh2..   548.771094: irq_noise: call_function_single:251 start 548.771091719 duration 1932 ns
             cc1-87882   [005] dNLh2..   548.771096: irq_noise: call_function_single:251 start 548.771094696 duration 1050 ns
             cc1-87882   [005] d...3..   548.771101: thread_noise:      cc1:87882 start 548.771078243 duration 10909 ns
      timerlat/5-1035    [005] .......   548.771103: #402268 context thread timer_latency     25960 ns

For further information see: Documentation/trace/timerlat-tracer.rst

Link: https://lkml.kernel.org/r/71f18efc013e1194bcaea1e54db957de2b19ba62.1624372313.git.bristot@redhat.com

Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 Documentation/trace/index.rst           |   1 +
 Documentation/trace/timerlat-tracer.rst | 181 +++++++
 kernel/trace/Kconfig                    |  28 ++
 kernel/trace/trace.h                    |   2 +
 kernel/trace/trace_entries.h            |  16 +
 kernel/trace/trace_osnoise.c            | 626 ++++++++++++++++++++++--
 kernel/trace/trace_output.c             |  47 ++
 7 files changed, 870 insertions(+), 31 deletions(-)
 create mode 100644 Documentation/trace/timerlat-tracer.rst

diff --git a/Documentation/trace/index.rst b/Documentation/trace/index.rst
index 608107b27cc0..3769b9b7aed8 100644
--- a/Documentation/trace/index.rst
+++ b/Documentation/trace/index.rst
@@ -24,6 +24,7 @@ Linux Tracing Technologies
    boottime-trace
    hwlat_detector
    osnoise-tracer
+   timerlat-tracer
    intel_th
    ring-buffer-design
    stm
diff --git a/Documentation/trace/timerlat-tracer.rst b/Documentation/trace/timerlat-tracer.rst
new file mode 100644
index 000000000000..c7cbb557aee7
--- /dev/null
+++ b/Documentation/trace/timerlat-tracer.rst
@@ -0,0 +1,181 @@
+###############
+Timerlat tracer
+###############
+
+The timerlat tracer aims to help the preemptive kernel developers to
+find souces of wakeup latencies of real-time threads. Like cyclictest,
+the tracer sets a periodic timer that wakes up a thread. The thread then
+computes a *wakeup latency* value as the difference between the *current
+time* and the *absolute time* that the timer was set to expire. The main
+goal of timerlat is tracing in such a way to help kernel developers.
+
+Usage
+-----
+
+Write the ASCII text "timerlat" into the current_tracer file of the
+tracing system (generally mounted at /sys/kernel/tracing).
+
+For example::
+
+        [root@f32 ~]# cd /sys/kernel/tracing/
+        [root@f32 tracing]# echo timerlat > current_tracer
+
+It is possible to follow the trace by reading the trace trace file::
+
+  [root@f32 tracing]# cat trace
+  # tracer: timerlat
+  #
+  #                              _-----=> irqs-off
+  #                             / _----=> need-resched
+  #                            | / _---=> hardirq/softirq
+  #                            || / _--=> preempt-depth
+  #                            || /
+  #                            ||||             ACTIVATION
+  #         TASK-PID      CPU# ||||   TIMESTAMP    ID            CONTEXT                LATENCY
+  #            | |         |   ||||      |         |                  |                       |
+          <idle>-0       [000] d.h1    54.029328: #1     context    irq timer_latency       932 ns
+           <...>-867     [000] ....    54.029339: #1     context thread timer_latency     11700 ns
+          <idle>-0       [001] dNh1    54.029346: #1     context    irq timer_latency      2833 ns
+           <...>-868     [001] ....    54.029353: #1     context thread timer_latency      9820 ns
+          <idle>-0       [000] d.h1    54.030328: #2     context    irq timer_latency       769 ns
+           <...>-867     [000] ....    54.030330: #2     context thread timer_latency      3070 ns
+          <idle>-0       [001] d.h1    54.030344: #2     context    irq timer_latency       935 ns
+           <...>-868     [001] ....    54.030347: #2     context thread timer_latency      4351 ns
+
+
+The tracer creates a per-cpu kernel thread with real-time priority that
+prints two lines at every activation. The first is the *timer latency*
+observed at the *hardirq* context before the activation of the thread.
+The second is the *timer latency* observed by the thread. The ACTIVATION
+ID field serves to relate the *irq* execution to its respective *thread*
+execution.
+
+The *irq*/*thread* splitting is important to clarify at which context
+the unexpected high value is coming from. The *irq* context can be
+delayed by hardware related actions, such as SMIs, NMIs, IRQs
+or by a thread masking interrupts. Once the timer happens, the delay
+can also be influenced by blocking caused by threads. For example, by
+postponing the scheduler execution via preempt_disable(), by the
+scheduler execution, or by masking interrupts. Threads can
+also be delayed by the interference from other threads and IRQs.
+
+Tracer options
+---------------------
+
+The timerlat tracer is built on top of osnoise tracer.
+So its configuration is also done in the osnoise/ config
+directory. The timerlat configs are:
+
+ - cpus: CPUs at which a timerlat thread will execute.
+ - timerlat_period_us: the period of the timerlat thread.
+ - osnoise/stop_tracing_us: stop the system tracing if a
+   timer latency at the *irq* context higher than the configured
+   value happens. Writing 0 disables this option.
+ - stop_tracing_total_us: stop the system tracing if a
+   timer latency at the *thread* context higher than the configured
+   value happens. Writing 0 disables this option.
+ - print_stack: save the stack of the IRQ ocurrence, and print
+   it afte the *thread context* event".
+
+timerlat and osnoise
+----------------------------
+
+The timerlat can also take advantage of the osnoise: traceevents.
+For example::
+
+        [root@f32 ~]# cd /sys/kernel/tracing/
+        [root@f32 tracing]# echo timerlat > current_tracer
+        [root@f32 tracing]# echo 1 > events/osnoise/enable
+        [root@f32 tracing]# echo 25 > osnoise/stop_tracing_total_us
+        [root@f32 tracing]# tail -10 trace
+             cc1-87882   [005] d..h...   548.771078: #402268 context    irq timer_latency     13585 ns
+             cc1-87882   [005] dNLh1..   548.771082: irq_noise: local_timer:236 start 548.771077442 duration 7597 ns
+             cc1-87882   [005] dNLh2..   548.771099: irq_noise: qxl:21 start 548.771085017 duration 7139 ns
+             cc1-87882   [005] d...3..   548.771102: thread_noise:      cc1:87882 start 548.771078243 duration 9909 ns
+      timerlat/5-1035    [005] .......   548.771104: #402268 context thread timer_latency     39960 ns
+
+In this case, the root cause of the timer latency does not point to a
+single cause, but to multiple ones. Firstly, the timer IRQ was delayed
+for 13 us, which may point to a long IRQ disabled section (see IRQ
+stacktrace section). Then the timer interrupt that wakes up the timerlat
+thread took 7597 ns, and the qxl:21 device IRQ took 7139 ns. Finally,
+the cc1 thread noise took 9909 ns of time before the context switch.
+Such pieces of evidence are useful for the developer to use other
+tracing methods to figure out how to debug and optimize the system.
+
+It is worth mentioning that the *duration* values reported
+by the osnoise: events are *net* values. For example, the
+thread_noise does not include the duration of the overhead caused
+by the IRQ execution (which indeed accounted for 12736 ns). But
+the values reported by the timerlat tracer (timerlat_latency)
+are *gross* values.
+
+The art below illustrates a CPU timeline and how the timerlat tracer
+observes it at the top and the osnoise: events at the bottom. Each "-"
+in the timelines means circa 1 us, and the time moves ==>::
+
+      External     timer irq                   thread
+       clock        latency                    latency
+       event        13585 ns                   39960 ns
+         |             ^                         ^
+         v             |                         |
+         |-------------|                         |
+         |-------------+-------------------------|
+                       ^                         ^
+  ========================================================================
+                    [tmr irq]  [dev irq]
+  [another thread...^       v..^       v.......][timerlat/ thread]  <-- CPU timeline
+  =========================================================================
+                    |-------|  |-------|
+                            |--^       v-------|
+                            |          |       |
+                            |          |       + thread_noise: 9909 ns
+                            |          +-> irq_noise: 6139 ns
+                            +-> irq_noise: 7597 ns
+
+IRQ stacktrace
+---------------------------
+
+The osnoise/print_stack option is helpful for the cases in which a thread
+noise causes the major factor for the timer latency, because of preempt or
+irq disabled. For example::
+
+        [root@f32 tracing]# echo 500 > osnoise/stop_tracing_total_us
+        [root@f32 tracing]# echo 500 > osnoise/print_stack
+        [root@f32 tracing]# echo timerlat > current_tracer
+        [root@f32 tracing]# tail -21 per_cpu/cpu7/trace
+          insmod-1026    [007] dN.h1..   200.201948: irq_noise: local_timer:236 start 200.201939376 duration 7872 ns
+          insmod-1026    [007] d..h1..   200.202587: #29800 context    irq timer_latency      1616 ns
+          insmod-1026    [007] dN.h2..   200.202598: irq_noise: local_timer:236 start 200.202586162 duration 11855 ns
+          insmod-1026    [007] dN.h3..   200.202947: irq_noise: local_timer:236 start 200.202939174 duration 7318 ns
+          insmod-1026    [007] d...3..   200.203444: thread_noise:   insmod:1026 start 200.202586933 duration 838681 ns
+      timerlat/7-1001    [007] .......   200.203445: #29800 context thread timer_latency    859978 ns
+      timerlat/7-1001    [007] ....1..   200.203446: <stack trace>
+  => timerlat_irq
+  => __hrtimer_run_queues
+  => hrtimer_interrupt
+  => __sysvec_apic_timer_interrupt
+  => asm_call_irq_on_stack
+  => sysvec_apic_timer_interrupt
+  => asm_sysvec_apic_timer_interrupt
+  => delay_tsc
+  => dummy_load_1ms_pd_init
+  => do_one_initcall
+  => do_init_module
+  => __do_sys_finit_module
+  => do_syscall_64
+  => entry_SYSCALL_64_after_hwframe
+
+In this case, it is possible to see that the thread added the highest
+contribution to the *timer latency* and the stack trace, saved during
+the timerlat IRQ handler, points to a function named
+dummy_load_1ms_pd_init, which had the following code (on purpose)::
+
+	static int __init dummy_load_1ms_pd_init(void)
+	{
+		preempt_disable();
+		mdelay(1);
+		preempt_enable();
+		return 0;
+
+	}
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 41582ae4682b..d567b1717c4c 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -390,6 +390,34 @@ config OSNOISE_TRACER
 	  To enable this tracer, echo in "osnoise" into the current_tracer
           file.
 
+config TIMERLAT_TRACER
+	bool "Timerlat tracer"
+	select OSNOISE_TRACER
+	select GENERIC_TRACER
+	help
+	  The timerlat tracer aims to help the preemptive kernel developers
+	  to find sources of wakeup latencies of real-time threads.
+
+	  The tracer creates a per-cpu kernel thread with real-time priority.
+	  The tracer thread sets a periodic timer to wakeup itself, and goes
+	  to sleep waiting for the timer to fire. At the wakeup, the thread
+	  then computes a wakeup latency value as the difference between
+	  the current time and the absolute time that the timer was set
+	  to expire.
+
+	  The tracer prints two lines at every activation. The first is the
+	  timer latency observed at the hardirq context before the
+	  activation of the thread. The second is the timer latency observed
+	  by the thread, which is the same level that cyclictest reports. The
+	  ACTIVATION ID field serves to relate the irq execution to its
+	  respective thread execution.
+
+	  The tracer is build on top of osnoise tracer, and the osnoise:
+	  events can be used to trace the source of interference from NMI,
+	  IRQs and other threads. It also enables the capture of the
+	  stacktrace at the IRQ context, which helps to identify the code
+	  path that can cause thread delay.
+
 config MMIOTRACE
 	bool "Memory mapped IO tracing"
 	depends on HAVE_MMIOTRACE_SUPPORT && PCI
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index b959c9ec9711..d83bbb6859b4 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -45,6 +45,7 @@ enum trace_type {
 	TRACE_BPUTS,
 	TRACE_HWLAT,
 	TRACE_OSNOISE,
+	TRACE_TIMERLAT,
 	TRACE_RAW_DATA,
 	TRACE_FUNC_REPEATS,
 
@@ -448,6 +449,7 @@ extern void __ftrace_bad_type(void);
 		IF_ASSIGN(var, ent, struct bputs_entry, TRACE_BPUTS);	\
 		IF_ASSIGN(var, ent, struct hwlat_entry, TRACE_HWLAT);	\
 		IF_ASSIGN(var, ent, struct osnoise_entry, TRACE_OSNOISE);\
+		IF_ASSIGN(var, ent, struct timerlat_entry, TRACE_TIMERLAT);\
 		IF_ASSIGN(var, ent, struct raw_data_entry, TRACE_RAW_DATA);\
 		IF_ASSIGN(var, ent, struct trace_mmiotrace_rw,		\
 			  TRACE_MMIO_RW);				\
diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
index 158c0984b59b..cd41e863b51c 100644
--- a/kernel/trace/trace_entries.h
+++ b/kernel/trace/trace_entries.h
@@ -385,3 +385,19 @@ FTRACE_ENTRY(osnoise, osnoise_entry,
 		 __entry->softirq_count,
 		 __entry->thread_count)
 );
+
+FTRACE_ENTRY(timerlat, timerlat_entry,
+
+	TRACE_TIMERLAT,
+
+	F_STRUCT(
+		__field(	unsigned int,		seqnum		)
+		__field(	int,			context		)
+		__field(	u64,			timer_latency	)
+	),
+
+	F_printk("seq:%u\tcontext:%d\ttimer_latency:%llu\n",
+		 __entry->seqnum,
+		 __entry->context,
+		 __entry->timer_latency)
+);
diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 4e2c47dc4f19..8546e66bafcb 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 /*
  * OS Noise Tracer: computes the OS Noise suffered by a running thread.
+ * Timerlat Tracer: measures the wakeup latency of a timer triggered IRQ and thread.
  *
  * Based on "hwlat_detector" tracer by:
  *   Copyright (C) 2008-2009 Jon Masters, Red Hat, Inc. <jcm@redhat.com>
@@ -21,6 +22,7 @@
 #include <linux/cpumask.h>
 #include <linux/delay.h>
 #include <linux/sched/clock.h>
+#include <uapi/linux/sched/types.h>
 #include <linux/sched.h>
 #include "trace.h"
 
@@ -45,6 +47,9 @@ static struct trace_array	*osnoise_trace;
 #define DEFAULT_SAMPLE_PERIOD	1000000			/* 1s */
 #define DEFAULT_SAMPLE_RUNTIME	1000000			/* 1s */
 
+#define DEFAULT_TIMERLAT_PERIOD	1000			/* 1ms */
+#define DEFAULT_TIMERLAT_PRIO	95			/* FIFO 95 */
+
 /*
  * NMI runtime info.
  */
@@ -62,6 +67,8 @@ struct osn_irq {
 	u64	delta_start;
 };
 
+#define IRQ_CONTEXT	0
+#define THREAD_CONTEXT	1
 /*
  * sofirq runtime info.
  */
@@ -108,32 +115,76 @@ static inline struct osnoise_variables *this_cpu_osn_var(void)
 	return this_cpu_ptr(&per_cpu_osnoise_var);
 }
 
+#ifdef CONFIG_TIMERLAT_TRACER
 /*
- * osn_var_reset - Reset the values of the given osnoise_variables
+ * Runtime information for the timer mode.
+ */
+struct timerlat_variables {
+	struct task_struct	*kthread;
+	struct hrtimer		timer;
+	u64			rel_period;
+	u64			abs_period;
+	bool			tracing_thread;
+	u64			count;
+};
+
+DEFINE_PER_CPU(struct timerlat_variables, per_cpu_timerlat_var);
+
+/*
+ * this_cpu_tmr_var - Return the per-cpu timerlat_variables on its relative CPU
+ */
+static inline struct timerlat_variables *this_cpu_tmr_var(void)
+{
+	return this_cpu_ptr(&per_cpu_timerlat_var);
+}
+
+/*
+ * tlat_var_reset - Reset the values of the given timerlat_variables
  */
-static inline void osn_var_reset(struct osnoise_variables *osn_var)
+static inline void tlat_var_reset(void)
 {
+	struct timerlat_variables *tlat_var;
+	int cpu;
 	/*
 	 * So far, all the values are initialized as 0, so
 	 * zeroing the structure is perfect.
 	 */
-	memset(osn_var, 0, sizeof(*osn_var));
+	for_each_cpu(cpu, cpu_online_mask) {
+		tlat_var = per_cpu_ptr(&per_cpu_timerlat_var, cpu);
+		memset(tlat_var, 0, sizeof(*tlat_var));
+	}
 }
+#else /* CONFIG_TIMERLAT_TRACER */
+#define tlat_var_reset()	do {} while (0)
+#endif /* CONFIG_TIMERLAT_TRACER */
 
 /*
- * osn_var_reset_all - Reset the value of all per-cpu osnoise_variables
+ * osn_var_reset - Reset the values of the given osnoise_variables
  */
-static inline void osn_var_reset_all(void)
+static inline void osn_var_reset(void)
 {
 	struct osnoise_variables *osn_var;
 	int cpu;
 
+	/*
+	 * So far, all the values are initialized as 0, so
+	 * zeroing the structure is perfect.
+	 */
 	for_each_cpu(cpu, cpu_online_mask) {
 		osn_var = per_cpu_ptr(&per_cpu_osnoise_var, cpu);
-		osn_var_reset(osn_var);
+		memset(osn_var, 0, sizeof(*osn_var));
 	}
 }
 
+/*
+ * osn_var_reset_all - Reset the value of all per-cpu osnoise_variables
+ */
+static inline void osn_var_reset_all(void)
+{
+	osn_var_reset();
+	tlat_var_reset();
+}
+
 /*
  * Tells NMIs to call back to the osnoise tracer to record timestamps.
  */
@@ -154,6 +205,18 @@ struct osnoise_sample {
 	int			thread_count;	/* # threads during this sample */
 };
 
+#ifdef CONFIG_TIMERLAT_TRACER
+/*
+ * timerlat sample structure definition. Used to store the statistics of
+ * a sample run.
+ */
+struct timerlat_sample {
+	u64			timer_latency;	/* timer_latency */
+	unsigned int		seqnum;		/* unique sequence */
+	int			context;	/* timer context */
+};
+#endif
+
 /*
  * Protect the interface.
  */
@@ -165,14 +228,24 @@ struct mutex interface_lock;
 static struct osnoise_data {
 	u64	sample_period;		/* total sampling period */
 	u64	sample_runtime;		/* active sampling portion of period */
-	u64	stop_tracing;		/* stop trace in the inside operation (loop) */
-	u64	stop_tracing_total;	/* stop trace in the outside operation (report) */
+	u64	stop_tracing;		/* stop trace in the internal operation (loop/irq) */
+	u64	stop_tracing_total;	/* stop trace in the final operation (report/thread) */
+#ifdef CONFIG_TIMERLAT_TRACER
+	u64	timerlat_period;	/* timerlat period */
+	u64	print_stack;		/* print IRQ stack if total > */
+	int	timerlat_tracer;	/* timerlat tracer */
+#endif
 	bool	tainted;		/* infor users and developers about a problem */
 } osnoise_data = {
 	.sample_period			= DEFAULT_SAMPLE_PERIOD,
 	.sample_runtime			= DEFAULT_SAMPLE_RUNTIME,
 	.stop_tracing			= 0,
 	.stop_tracing_total		= 0,
+#ifdef CONFIG_TIMERLAT_TRACER
+	.print_stack			= 0,
+	.timerlat_period		= DEFAULT_TIMERLAT_PERIOD,
+	.timerlat_tracer		= 0,
+#endif
 };
 
 /*
@@ -246,6 +319,128 @@ static void trace_osnoise_sample(struct osnoise_sample *sample)
 		trace_buffer_unlock_commit_nostack(buffer, event);
 }
 
+#ifdef CONFIG_TIMERLAT_TRACER
+/*
+ * Print the timerlat header info.
+ */
+static void print_timerlat_headers(struct seq_file *s)
+{
+	seq_puts(s, "#                                _-----=> irqs-off\n");
+	seq_puts(s, "#                               / _----=> need-resched\n");
+	seq_puts(s, "#                              | / _---=> hardirq/softirq\n");
+	seq_puts(s, "#                              || / _--=> preempt-depth\n");
+	seq_puts(s, "#                              || /\n");
+	seq_puts(s, "#                              ||||             ACTIVATION\n");
+	seq_puts(s, "#           TASK-PID      CPU# ||||   TIMESTAMP    ID     ");
+	seq_puts(s, "       CONTEXT                LATENCY\n");
+	seq_puts(s, "#              | |         |   ||||      |         |      ");
+	seq_puts(s, "            |                       |\n");
+}
+
+/*
+ * Record an timerlat_sample into the tracer buffer.
+ */
+static void trace_timerlat_sample(struct timerlat_sample *sample)
+{
+	struct trace_array *tr = osnoise_trace;
+	struct trace_event_call *call = &event_osnoise;
+	struct trace_buffer *buffer = tr->array_buffer.buffer;
+	struct ring_buffer_event *event;
+	struct timerlat_entry *entry;
+
+	event = trace_buffer_lock_reserve(buffer, TRACE_TIMERLAT, sizeof(*entry),
+					  tracing_gen_ctx());
+	if (!event)
+		return;
+	entry	= ring_buffer_event_data(event);
+	entry->seqnum			= sample->seqnum;
+	entry->context			= sample->context;
+	entry->timer_latency		= sample->timer_latency;
+
+	if (!call_filter_check_discard(call, entry, buffer, event))
+		trace_buffer_unlock_commit_nostack(buffer, event);
+}
+
+#ifdef CONFIG_STACKTRACE
+
+#define	MAX_CALLS	256
+
+/*
+ * Stack trace will take place only at IRQ level, so, no need
+ * to control nesting here.
+ */
+struct trace_stack {
+	int		stack_size;
+	int		nr_entries;
+	unsigned long	calls[MAX_CALLS];
+};
+
+static DEFINE_PER_CPU(struct trace_stack, trace_stack);
+
+/*
+ * timerlat_save_stack - save a stack trace without printing
+ *
+ * Save the current stack trace without printing. The
+ * stack will be printed later, after the end of the measurement.
+ */
+static void timerlat_save_stack(int skip)
+{
+	unsigned int size, nr_entries;
+	struct trace_stack *fstack;
+
+	fstack = this_cpu_ptr(&trace_stack);
+
+	size = ARRAY_SIZE(fstack->calls);
+
+	nr_entries = stack_trace_save(fstack->calls, size, skip);
+
+	fstack->stack_size = nr_entries * sizeof(unsigned long);
+	fstack->nr_entries = nr_entries;
+
+	return;
+
+}
+/*
+ * timerlat_dump_stack - dump a stack trace previously saved
+ *
+ * Dump a saved stack trace into the trace buffer.
+ */
+static void timerlat_dump_stack(void)
+{
+	struct trace_event_call *call = &event_osnoise;
+	struct trace_array *tr = osnoise_trace;
+	struct trace_buffer *buffer = tr->array_buffer.buffer;
+	struct ring_buffer_event *event;
+	struct trace_stack *fstack;
+	struct stack_entry *entry;
+	unsigned int size;
+
+	preempt_disable_notrace();
+	fstack = this_cpu_ptr(&trace_stack);
+	size = fstack->stack_size;
+
+	event = trace_buffer_lock_reserve(buffer, TRACE_STACK, sizeof(*entry) + size,
+					  tracing_gen_ctx());
+	if (!event)
+		goto out;
+
+	entry = ring_buffer_event_data(event);
+
+	memcpy(&entry->caller, fstack->calls, size);
+	entry->size = fstack->nr_entries;
+
+	if (!call_filter_check_discard(call, entry, buffer, event))
+		trace_buffer_unlock_commit_nostack(buffer, event);
+
+out:
+	preempt_enable_notrace();
+}
+#else
+#define timerlat_dump_stack() do {} while (0)
+#define timerlat_save_stack(a) do {} while (0)
+#endif /* CONFIG_STACKTRACE */
+#endif /* CONFIG_TIMERLAT_TRACER */
+
 /*
  * Macros to encapsulate the time capturing infrastructure.
  */
@@ -387,6 +582,30 @@ set_int_safe_time(struct osnoise_variables *osn_var, u64 *time)
 	return int_counter;
 }
 
+#ifdef CONFIG_TIMERLAT_TRACER
+/*
+ * copy_int_safe_time - Copy *src into *desc aware of interference
+ */
+static u64
+copy_int_safe_time(struct osnoise_variables *osn_var, u64 *dst, u64 *src)
+{
+	u64 int_counter;
+
+	do {
+		int_counter = local_read(&osn_var->int_counter);
+		/* synchronize with interrupts */
+		barrier();
+
+		*dst = *src;
+
+		/* synchronize with interrupts */
+		barrier();
+	} while (int_counter != local_read(&osn_var->int_counter));
+
+	return int_counter;
+}
+#endif /* CONFIG_TIMERLAT_TRACER */
+
 /*
  * trace_osnoise_callback - NMI entry/exit callback
  *
@@ -597,6 +816,22 @@ void trace_softirq_exit_callback(void *data, unsigned int vec_nr)
 	if (!osn_var->sampling)
 		return;
 
+#ifdef CONFIG_TIMERLAT_TRACER
+	/*
+	 * If the timerlat is enabled, but the irq handler did
+	 * not run yet enabling timerlat_tracer, do not trace.
+	 */
+	if (unlikely(osnoise_data.timerlat_tracer)) {
+		struct timerlat_variables *tlat_var;
+		tlat_var = this_cpu_tmr_var();
+		if (!tlat_var->tracing_thread) {
+			osn_var->softirq.arrival_time = 0;
+			osn_var->softirq.delta_start = 0;
+			return;
+		}
+	}
+#endif
+
 	duration = get_int_safe_duration(osn_var, &osn_var->softirq.delta_start);
 	trace_softirq_noise(vec_nr, osn_var->softirq.arrival_time, duration);
 	cond_move_thread_delta_start(osn_var, duration);
@@ -689,6 +924,18 @@ thread_exit(struct osnoise_variables *osn_var, struct task_struct *t)
 	if (!osn_var->sampling)
 		return;
 
+#ifdef CONFIG_TIMERLAT_TRACER
+	if (osnoise_data.timerlat_tracer) {
+		struct timerlat_variables *tlat_var;
+		tlat_var = this_cpu_tmr_var();
+		if (!tlat_var->tracing_thread) {
+			osn_var->thread.delta_start = 0;
+			osn_var->thread.arrival_time = 0;
+			return;
+		}
+	}
+#endif
+
 	duration = get_int_safe_duration(osn_var, &osn_var->thread.delta_start);
 
 	trace_thread_noise(t, osn_var->thread.arrival_time, duration);
@@ -979,6 +1226,195 @@ static int osnoise_main(void *data)
 	return 0;
 }
 
+#ifdef CONFIG_TIMERLAT_TRACER
+/*
+ * timerlat_irq - hrtimer handler for timerlat.
+ */
+static enum hrtimer_restart timerlat_irq(struct hrtimer *timer)
+{
+	struct osnoise_variables *osn_var = this_cpu_osn_var();
+	struct trace_array *tr = osnoise_trace;
+	struct timerlat_variables *tlat;
+	struct timerlat_sample s;
+	u64 now;
+	u64 diff;
+
+	/*
+	 * I am not sure if the timer was armed for this CPU. So, get
+	 * the timerlat struct from the timer itself, not from this
+	 * CPU.
+	 */
+	tlat = container_of(timer, struct timerlat_variables, timer);
+
+	now = ktime_to_ns(hrtimer_cb_get_time(&tlat->timer));
+
+	/*
+	 * Enable the osnoise: events for thread an softirq.
+	 */
+	tlat->tracing_thread = true;
+
+	osn_var->thread.arrival_time = time_get();
+
+	/*
+	 * A hardirq is running: the timer IRQ. It is for sure preempting
+	 * a thread, and potentially preempting a softirq.
+	 *
+	 * At this point, it is not interesting to know the duration of the
+	 * preempted thread (and maybe softirq), but how much time they will
+	 * delay the beginning of the execution of the timer thread.
+	 *
+	 * To get the correct (net) delay added by the softirq, its delta_start
+	 * is set as the IRQ one. In this way, at the return of the IRQ, the delta
+	 * start of the sofitrq will be zeroed, accounting then only the time
+	 * after that.
+	 *
+	 * The thread follows the same principle. However, if a softirq is
+	 * running, the thread needs to receive the softirq delta_start. The
+	 * reason being is that the softirq will be the last to be unfolded,
+	 * resseting the thread delay to zero.
+	 */
+#ifndef CONFIG_PREEMPT_RT
+	if (osn_var->softirq.delta_start) {
+		copy_int_safe_time(osn_var, &osn_var->thread.delta_start,
+				   &osn_var->softirq.delta_start);
+
+		copy_int_safe_time(osn_var, &osn_var->softirq.delta_start,
+				    &osn_var->irq.delta_start);
+	} else {
+		copy_int_safe_time(osn_var, &osn_var->thread.delta_start,
+				    &osn_var->irq.delta_start);
+	}
+#else /* CONFIG_PREEMPT_RT */
+	/*
+	 * The sofirqs run as threads on RT, so there is not need
+	 * to keep track of it.
+	 */
+	copy_int_safe_time(osn_var, &osn_var->thread.delta_start, &osn_var->irq.delta_start);
+#endif /* CONFIG_PREEMPT_RT */
+
+	/*
+	 * Compute the current time with the expected time.
+	 */
+	diff = now - tlat->abs_period;
+
+	tlat->count++;
+	s.seqnum = tlat->count;
+	s.timer_latency = diff;
+	s.context = IRQ_CONTEXT;
+
+	trace_timerlat_sample(&s);
+
+	/* Keep a running maximum ever recorded os noise "latency" */
+	if (diff > tr->max_latency) {
+		tr->max_latency = diff;
+		latency_fsnotify(tr);
+	}
+
+	if (osnoise_data.stop_tracing)
+		if (time_to_us(diff) >= osnoise_data.stop_tracing)
+			osnoise_stop_tracing();
+
+	wake_up_process(tlat->kthread);
+
+	if (osnoise_data.print_stack)
+		timerlat_save_stack(0);
+
+	return HRTIMER_NORESTART;
+}
+
+/*
+ * wait_next_period - Wait for the next period for timerlat
+ */
+static int wait_next_period(struct timerlat_variables *tlat)
+{
+	ktime_t next_abs_period, now;
+	u64 rel_period = osnoise_data.timerlat_period * 1000;
+
+	now = hrtimer_cb_get_time(&tlat->timer);
+	next_abs_period = ns_to_ktime(tlat->abs_period + rel_period);
+
+	/*
+	 * Save the next abs_period.
+	 */
+	tlat->abs_period = (u64) ktime_to_ns(next_abs_period);
+
+	/*
+	 * If the new abs_period is in the past, skip the activation.
+	 */
+	while (ktime_compare(now, next_abs_period) > 0) {
+		next_abs_period = ns_to_ktime(tlat->abs_period + rel_period);
+		tlat->abs_period = (u64) ktime_to_ns(next_abs_period);
+	}
+
+	set_current_state(TASK_INTERRUPTIBLE);
+
+	hrtimer_start(&tlat->timer, next_abs_period, HRTIMER_MODE_ABS_PINNED_HARD);
+	schedule();
+	return 1;
+}
+
+/*
+ * timerlat_main- Timerlat main
+ */
+static int timerlat_main(void *data)
+{
+	struct osnoise_variables *osn_var = this_cpu_osn_var();
+	struct timerlat_variables *tlat = this_cpu_tmr_var();
+	struct timerlat_sample s;
+	struct sched_param sp;
+	u64 now, diff;
+
+	/*
+	 * Make the thread RT, that is how cyclictest is usually used.
+	 */
+	sp.sched_priority = DEFAULT_TIMERLAT_PRIO;
+	sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
+
+	tlat->count = 0;
+	tlat->tracing_thread = false;
+
+	hrtimer_init(&tlat->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED_HARD);
+	tlat->timer.function = timerlat_irq;
+	tlat->kthread = current;
+	osn_var->pid = current->pid;
+	/*
+	 * Anotate the arrival time.
+	 */
+	tlat->abs_period = hrtimer_cb_get_time(&tlat->timer);
+
+	wait_next_period(tlat);
+
+	osn_var->sampling = 1;
+
+	while (!kthread_should_stop()) {
+		now = ktime_to_ns(hrtimer_cb_get_time(&tlat->timer));
+		diff = now - tlat->abs_period;
+
+		s.seqnum = tlat->count;
+		s.timer_latency = diff;
+		s.context = THREAD_CONTEXT;
+
+		trace_timerlat_sample(&s);
+
+#ifdef CONFIG_STACKTRACE
+	if (osnoise_data.print_stack)
+		if (osnoise_data.print_stack <= time_to_us(diff))
+			timerlat_dump_stack();
+#endif /* CONFIG_STACKTRACE */
+
+		tlat->tracing_thread = false;
+		if (osnoise_data.stop_tracing_total)
+			if (time_to_us(diff) >= osnoise_data.stop_tracing_total)
+				osnoise_stop_tracing();
+
+		wait_next_period(tlat);
+	}
+
+	hrtimer_cancel(&tlat->timer);
+	return 0;
+}
+#endif /* CONFIG_TIMERLAT_TRACER */
+
 /*
  * stop_per_cpu_kthread - stop per-cpu threads
  *
@@ -1009,6 +1445,7 @@ static int start_per_cpu_kthreads(struct trace_array *tr)
 	struct cpumask *current_mask = &save_cpumask;
 	struct task_struct *kthread;
 	char comm[24];
+	void *main = osnoise_main;
 	int cpu;
 
 	get_online_cpus();
@@ -1026,9 +1463,17 @@ static int start_per_cpu_kthreads(struct trace_array *tr)
 		per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;
 
 	for_each_cpu(cpu, current_mask) {
+#ifdef CONFIG_TIMERLAT_TRACER
+		if (osnoise_data.timerlat_tracer) {
+			snprintf(comm, 24, "timerlat/%d", cpu);
+			main = timerlat_main;
+		} else {
+			snprintf(comm, 24, "osnoise/%d", cpu);
+		}
+#else
 		snprintf(comm, 24, "osnoise/%d", cpu);
-
-		kthread = kthread_create_on_cpu(osnoise_main, NULL, cpu, comm);
+#endif
+		kthread = kthread_create_on_cpu(main, NULL, cpu, comm);
 
 		if (IS_ERR(kthread)) {
 			pr_err(BANNER "could not start sampling thread\n");
@@ -1194,6 +1639,31 @@ static struct trace_min_max_param osnoise_stop_tracing_total = {
 	.min	= NULL,
 };
 
+#ifdef CONFIG_TIMERLAT_TRACER
+/*
+ * osnoise/print_stack: print the stacktrace of the IRQ handler if the total
+ * latency is higher than val.
+ */
+static struct trace_min_max_param osnoise_print_stack = {
+	.lock	= &interface_lock,
+	.val	= &osnoise_data.print_stack,
+	.max	= NULL,
+	.min	= NULL,
+};
+
+/*
+ * osnoise/timerlat_period: min 100 us, max 1 s
+ */
+u64 timerlat_min_period = 100;
+u64 timerlat_max_period = 1000000;
+static struct trace_min_max_param timerlat_period = {
+	.lock	= &interface_lock,
+	.val	= &osnoise_data.timerlat_period,
+	.max	= &timerlat_max_period,
+	.min	= &timerlat_min_period,
+};
+#endif
+
 static const struct file_operations cpus_fops = {
 	.open		= tracing_open_generic,
 	.read		= osnoise_cpus_read,
@@ -1204,10 +1674,9 @@ static const struct file_operations cpus_fops = {
 /*
  * init_tracefs - A function to initialize the tracefs interface files
  *
- * This function creates entries in tracefs for "osnoise". It creates the
- * "osnoise" directory in the tracing directory, and within that
- * directory is the count, runtime and period files to change and view
- * those values.
+ * This function creates entries in tracefs for "osnoise" and "timerlat".
+ * It creates these directories in the tracing directory, and within that
+ * directory the use can change and view the configs.
  */
 static int init_tracefs(void)
 {
@@ -1221,7 +1690,7 @@ static int init_tracefs(void)
 
 	top_dir = tracefs_create_dir("osnoise", NULL);
 	if (!top_dir)
-		return -ENOMEM;
+		return 0;
 
 	tmp = tracefs_create_file("period_us", 0640, top_dir,
 				  &osnoise_period, &trace_min_max_fops);
@@ -1246,6 +1715,19 @@ static int init_tracefs(void)
 	tmp = trace_create_file("cpus", 0644, top_dir, NULL, &cpus_fops);
 	if (!tmp)
 		goto err;
+#ifdef CONFIG_TIMERLAT_TRACER
+#ifdef CONFIG_STACKTRACE
+	tmp = tracefs_create_file("print_stack", 0640, top_dir,
+				  &osnoise_print_stack, &trace_min_max_fops);
+	if (!tmp)
+		goto err;
+#endif
+
+	tmp = tracefs_create_file("timerlat_period_us", 0640, top_dir,
+				  &timerlat_period, &trace_min_max_fops);
+	if (!tmp)
+		goto err;
+#endif
 
 	return 0;
 
@@ -1286,18 +1768,15 @@ static int osnoise_hook_events(void)
 	return -EINVAL;
 }
 
-static void osnoise_tracer_start(struct trace_array *tr)
+static int __osnoise_tracer_start(struct trace_array *tr)
 {
 	int retval;
 
-	if (osnoise_busy)
-		return;
-
 	osn_var_reset_all();
 
 	retval = osnoise_hook_events();
 	if (retval)
-		goto out_err;
+		return retval;
 	/*
 	 * Make sure NMIs see reseted values.
 	 */
@@ -1305,15 +1784,27 @@ static void osnoise_tracer_start(struct trace_array *tr)
 	trace_osnoise_callback_enabled = true;
 
 	retval = start_per_cpu_kthreads(tr);
-	/*
-	 * all fine!
-	 */
-	if (!retval)
+	if (retval) {
+		unhook_irq_events();
+		return retval;
+	}
+
+	osnoise_busy = true;
+
+	return 0;
+}
+
+static void osnoise_tracer_start(struct trace_array *tr)
+{
+	int retval;
+
+	if (osnoise_busy)
 		return;
 
-out_err:
-	unhook_irq_events();
-	pr_err(BANNER "Error starting osnoise tracer\n");
+	retval = __osnoise_tracer_start(tr);
+	if (retval)
+		pr_err(BANNER "Error starting osnoise tracer\n");
+
 }
 
 static void osnoise_tracer_stop(struct trace_array *tr)
@@ -1335,18 +1826,16 @@ static void osnoise_tracer_stop(struct trace_array *tr)
 
 static int osnoise_tracer_init(struct trace_array *tr)
 {
+
 	/* Only allow one instance to enable this */
 	if (osnoise_busy)
 		return -EBUSY;
 
 	osnoise_trace = tr;
-
 	tr->max_latency = 0;
 
 	osnoise_tracer_start(tr);
 
-	osnoise_busy = true;
-
 	return 0;
 }
 
@@ -1365,6 +1854,71 @@ static struct tracer osnoise_tracer __read_mostly = {
 	.allow_instances = true,
 };
 
+#ifdef CONFIG_TIMERLAT_TRACER
+static void timerlat_tracer_start(struct trace_array *tr)
+{
+	int retval;
+
+	if (osnoise_busy)
+		return;
+
+	osnoise_data.timerlat_tracer = 1;
+
+	retval = __osnoise_tracer_start(tr);
+	if (retval)
+		goto out_err;
+
+	return;
+out_err:
+	pr_err(BANNER "Error starting timerlat tracer\n");
+}
+
+static void timerlat_tracer_stop(struct trace_array *tr)
+{
+	int cpu;
+
+	if (!osnoise_busy)
+		return;
+
+	for_each_online_cpu(cpu)
+		per_cpu(per_cpu_osnoise_var, cpu).sampling = 0;
+
+	osnoise_tracer_stop(tr);
+
+	osnoise_data.timerlat_tracer = 0;
+}
+
+static int timerlat_tracer_init(struct trace_array *tr)
+{
+	/* Only allow one instance to enable this */
+	if (osnoise_busy)
+		return -EBUSY;
+
+	osnoise_trace = tr;
+
+	tr->max_latency = 0;
+
+	timerlat_tracer_start(tr);
+
+	return 0;
+}
+
+static void timerlat_tracer_reset(struct trace_array *tr)
+{
+	timerlat_tracer_stop(tr);
+}
+
+static struct tracer timerlat_tracer __read_mostly = {
+	.name		= "timerlat",
+	.init		= timerlat_tracer_init,
+	.reset		= timerlat_tracer_reset,
+	.start		= timerlat_tracer_start,
+	.stop		= timerlat_tracer_stop,
+	.print_header	= print_timerlat_headers,
+	.allow_instances = true,
+};
+#endif /* CONFIG_TIMERLAT_TRACER */
+
 __init static int init_osnoise_tracer(void)
 {
 	int ret;
@@ -1374,8 +1928,18 @@ __init static int init_osnoise_tracer(void)
 	cpumask_copy(&osnoise_cpumask, cpu_all_mask);
 
 	ret = register_tracer(&osnoise_tracer);
-	if (ret)
+	if (ret) {
+		pr_err(BANNER "Error registering osnoise!\n");
 		return ret;
+	}
+
+#ifdef CONFIG_TIMERLAT_TRACER
+	ret = register_tracer(&timerlat_tracer);
+	if (ret) {
+		pr_err(BANNER "Error registering timerlat\n");
+		return ret;
+	}
+#endif
 
 	init_tracefs();
 
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 642b6584eba5..a0bf446bb034 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -1301,6 +1301,52 @@ static struct trace_event trace_osnoise_event = {
 	.funcs		= &trace_osnoise_funcs,
 };
 
+/* TRACE_TIMERLAT */
+static enum print_line_t
+trace_timerlat_print(struct trace_iterator *iter, int flags,
+		     struct trace_event *event)
+{
+	struct trace_entry *entry = iter->ent;
+	struct trace_seq *s = &iter->seq;
+	struct timerlat_entry *field;
+
+	trace_assign_type(field, entry);
+
+	trace_seq_printf(s, "#%-5u context %6s timer_latency %9llu ns\n",
+			 field->seqnum,
+			 field->context ? "thread" : "irq",
+			 field->timer_latency);
+
+	return trace_handle_return(s);
+}
+
+static enum print_line_t
+trace_timerlat_raw(struct trace_iterator *iter, int flags,
+		   struct trace_event *event)
+{
+	struct timerlat_entry *field;
+	struct trace_seq *s = &iter->seq;
+
+	trace_assign_type(field, iter->ent);
+
+	trace_seq_printf(s, "%u %d %llu\n",
+			 field->seqnum,
+			 field->context,
+			 field->timer_latency);
+
+	return trace_handle_return(s);
+}
+
+static struct trace_event_functions trace_timerlat_funcs = {
+	.trace		= trace_timerlat_print,
+	.raw		= trace_timerlat_raw,
+};
+
+static struct trace_event trace_timerlat_event = {
+	.type		= TRACE_TIMERLAT,
+	.funcs		= &trace_timerlat_funcs,
+};
+
 /* TRACE_BPUTS */
 static enum print_line_t
 trace_bputs_print(struct trace_iterator *iter, int flags,
@@ -1512,6 +1558,7 @@ static struct trace_event *events[] __initdata = {
 	&trace_print_event,
 	&trace_hwlat_event,
 	&trace_osnoise_event,
+	&trace_timerlat_event,
 	&trace_raw_data_event,
 	&trace_func_repeats_event,
 	NULL
-- 
2.30.2

[for-next][PATCH 22/24] trace/hwlat: Protect kdata->kthread with get/put_online_cpus

[Steven Rostedt]

From: Daniel Bristot de Oliveira <bristot@redhat.com>

In preparation to the hotplug support, protect kdata->kthread
with get/put_online_cpus() to avoid concurrency with hotplug
operations.

Link: https://lore.kernel.org/linux-doc/20210621134636.5b332226@oasis.local.home/
Link: https://lkml.kernel.org/r/8bdb2a56f46abfd301d6fffbf43448380c09a6f5.1624372313.git.bristot@redhat.com

Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Suggested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace_hwlat.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index a625bfdb844e..20e31f79ebd9 100644
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -396,13 +396,19 @@ static int kthread_fn(void *data)
 static void stop_single_kthread(void)
 {
 	struct hwlat_kthread_data *kdata = get_cpu_data();
-	struct task_struct *kthread = kdata->kthread;
+	struct task_struct *kthread;
+
+	get_online_cpus();
+	kthread = kdata->kthread;
 
 	if (!kthread)
-		return;
+		goto out_put_cpus;
 
 	kthread_stop(kthread);
 	kdata->kthread = NULL;
+
+out_put_cpus:
+	put_online_cpus();
 }
 
 
@@ -419,20 +425,19 @@ static int start_single_kthread(struct trace_array *tr)
 	struct task_struct *kthread;
 	int next_cpu;
 
+	get_online_cpus();
 	if (kdata->kthread)
-		return 0;
+		goto out_put_cpus;
 
 	kthread = kthread_create(kthread_fn, NULL, "hwlatd");
 	if (IS_ERR(kthread)) {
 		pr_err(BANNER "could not start sampling thread\n");
+		put_online_cpus();
 		return -ENOMEM;
 	}
 
-
 	/* Just pick the first CPU on first iteration */
-	get_online_cpus();
 	cpumask_and(current_mask, cpu_online_mask, tr->tracing_cpumask);
-	put_online_cpus();
 
 	if (hwlat_data.thread_mode == MODE_ROUND_ROBIN) {
 		next_cpu = cpumask_first(current_mask);
@@ -446,6 +451,8 @@ static int start_single_kthread(struct trace_array *tr)
 	kdata->kthread = kthread;
 	wake_up_process(kthread);
 
+out_put_cpus:
+	put_online_cpus();
 	return 0;
 }
 
-- 
2.30.2

[for-next][PATCH 23/24] trace/hwlat: Support hotplug operations

[Steven Rostedt]

From: Daniel Bristot de Oliveira <bristot@redhat.com>

Enable and disable hwlat thread during cpu hotplug online
and offline operations, respectivelly.

Link: https://lore.kernel.org/linux-doc/20210621134636.5b332226@oasis.local.home/
Link: https://lkml.kernel.org/r/52012d25ea35491a0f8088b947864d8df8e25157.1624372313.git.bristot@redhat.com

Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Suggested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace_hwlat.c | 65 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index 20e31f79ebd9..a6c0cdaf4b87 100644
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -466,6 +466,7 @@ static void stop_cpu_kthread(unsigned int cpu)
 	kthread = per_cpu(hwlat_per_cpu_data, cpu).kthread;
 	if (kthread)
 		kthread_stop(kthread);
+	per_cpu(hwlat_per_cpu_data, cpu).kthread = NULL;
 }
 
 /*
@@ -506,6 +507,68 @@ static int start_cpu_kthread(unsigned int cpu)
 	return 0;
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+static void hwlat_hotplug_workfn(struct work_struct *dummy)
+{
+	struct trace_array *tr = hwlat_trace;
+	unsigned int cpu = smp_processor_id();
+
+	mutex_lock(&trace_types_lock);
+	mutex_lock(&hwlat_data.lock);
+	get_online_cpus();
+
+	if (!hwlat_busy || hwlat_data.thread_mode != MODE_PER_CPU)
+		goto out_unlock;
+
+	if (!cpumask_test_cpu(cpu, tr->tracing_cpumask))
+		goto out_unlock;
+
+	start_cpu_kthread(cpu);
+
+out_unlock:
+	put_online_cpus();
+	mutex_unlock(&hwlat_data.lock);
+	mutex_unlock(&trace_types_lock);
+}
+
+static DECLARE_WORK(hwlat_hotplug_work, hwlat_hotplug_workfn);
+
+/*
+ * hwlat_cpu_init - CPU hotplug online callback function
+ */
+static int hwlat_cpu_init(unsigned int cpu)
+{
+	schedule_work_on(cpu, &hwlat_hotplug_work);
+	return 0;
+}
+
+/*
+ * hwlat_cpu_die - CPU hotplug offline callback function
+ */
+static int hwlat_cpu_die(unsigned int cpu)
+{
+	stop_cpu_kthread(cpu);
+	return 0;
+}
+
+static void hwlat_init_hotplug_support(void)
+{
+	int ret;
+
+	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "trace/hwlat:online",
+				hwlat_cpu_init, hwlat_cpu_die);
+	if (ret < 0)
+		pr_warn(BANNER "Error to init cpu hotplug support\n");
+
+	return;
+}
+#else /* CONFIG_HOTPLUG_CPU */
+static void hwlat_init_hotplug_support(void)
+{
+	return;
+}
+#endif /* CONFIG_HOTPLUG_CPU */
+
 /*
  * start_per_cpu_kthreads - Kick off the hardware latency sampling/detector kthreads
  *
@@ -822,6 +885,8 @@ __init static int init_hwlat_tracer(void)
 	if (ret)
 		return ret;
 
+	hwlat_init_hotplug_support();
+
 	init_tracefs();
 
 	return 0;
-- 
2.30.2

[for-next][PATCH 24/24] trace/osnoise: Support hotplug operations

[Steven Rostedt]

From: Daniel Bristot de Oliveira <bristot@redhat.com>

Enable and disable osnoise/timerlat thread during on CPU hotplug online
and offline operations respectivelly.

Link: https://lore.kernel.org/linux-doc/20210621134636.5b332226@oasis.local.home/
Link: https://lkml.kernel.org/r/39f98590b3caeb3c32f09526214058efe0e9272a.1624372313.git.bristot@redhat.com

Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Suggested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace_osnoise.c | 165 ++++++++++++++++++++++++++++-------
 1 file changed, 135 insertions(+), 30 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 8546e66bafcb..38aa5e208ffd 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1416,22 +1416,67 @@ static int timerlat_main(void *data)
 #endif /* CONFIG_TIMERLAT_TRACER */
 
 /*
- * stop_per_cpu_kthread - stop per-cpu threads
+ * stop_kthread - stop a workload thread
+ */
+static void stop_kthread(unsigned int cpu)
+{
+	struct task_struct *kthread;
+
+	kthread = per_cpu(per_cpu_osnoise_var, cpu).kthread;
+	if (kthread)
+		kthread_stop(kthread);
+	per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;
+}
+
+/*
+ * stop_per_cpu_kthread - Stop per-cpu threads
  *
  * Stop the osnoise sampling htread. Use this on unload and at system
  * shutdown.
  */
 static void stop_per_cpu_kthreads(void)
 {
-	struct task_struct *kthread;
 	int cpu;
 
-	for_each_online_cpu(cpu) {
-		kthread = per_cpu(per_cpu_osnoise_var, cpu).kthread;
-		if (kthread)
-			kthread_stop(kthread);
-		per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;
+	get_online_cpus();
+
+	for_each_online_cpu(cpu)
+		stop_kthread(cpu);
+
+	put_online_cpus();
+}
+
+/*
+ * start_kthread - Start a workload tread
+ */
+static int start_kthread(unsigned int cpu)
+{
+	struct task_struct *kthread;
+	void *main = osnoise_main;
+	char comm[24];
+
+#ifdef CONFIG_TIMERLAT_TRACER
+	if (osnoise_data.timerlat_tracer) {
+		snprintf(comm, 24, "timerlat/%d", cpu);
+		main = timerlat_main;
+	} else {
+		snprintf(comm, 24, "osnoise/%d", cpu);
 	}
+#else
+	snprintf(comm, 24, "osnoise/%d", cpu);
+#endif
+	kthread = kthread_create_on_cpu(main, NULL, cpu, comm);
+
+	if (IS_ERR(kthread)) {
+		pr_err(BANNER "could not start sampling thread\n");
+		stop_per_cpu_kthreads();
+		return -ENOMEM;
+	}
+
+	per_cpu(per_cpu_osnoise_var, cpu).kthread = kthread;
+	wake_up_process(kthread);
+
+	return 0;
 }
 
 /*
@@ -1443,9 +1488,7 @@ static void stop_per_cpu_kthreads(void)
 static int start_per_cpu_kthreads(struct trace_array *tr)
 {
 	struct cpumask *current_mask = &save_cpumask;
-	struct task_struct *kthread;
-	char comm[24];
-	void *main = osnoise_main;
+	int retval;
 	int cpu;
 
 	get_online_cpus();
@@ -1457,37 +1500,91 @@ static int start_per_cpu_kthreads(struct trace_array *tr)
 	 * And the CPU is online.
 	 */
 	cpumask_and(current_mask, cpu_online_mask, current_mask);
-	put_online_cpus();
 
-	for_each_online_cpu(cpu)
+	for_each_possible_cpu(cpu)
 		per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;
 
 	for_each_cpu(cpu, current_mask) {
-#ifdef CONFIG_TIMERLAT_TRACER
-		if (osnoise_data.timerlat_tracer) {
-			snprintf(comm, 24, "timerlat/%d", cpu);
-			main = timerlat_main;
-		} else {
-			snprintf(comm, 24, "osnoise/%d", cpu);
-		}
-#else
-		snprintf(comm, 24, "osnoise/%d", cpu);
-#endif
-		kthread = kthread_create_on_cpu(main, NULL, cpu, comm);
-
-		if (IS_ERR(kthread)) {
-			pr_err(BANNER "could not start sampling thread\n");
+		retval = start_kthread(cpu);
+		if (retval) {
 			stop_per_cpu_kthreads();
-			return -ENOMEM;
+			return retval;
 		}
-
-		per_cpu(per_cpu_osnoise_var, cpu).kthread = kthread;
-		wake_up_process(kthread);
 	}
 
+	put_online_cpus();
+
 	return 0;
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+static void osnoise_hotplug_workfn(struct work_struct *dummy)
+{
+	struct trace_array *tr = osnoise_trace;
+	unsigned int cpu = smp_processor_id();
+
+
+	mutex_lock(&trace_types_lock);
+
+	if (!osnoise_busy)
+		goto out_unlock_trace;
+
+	mutex_lock(&interface_lock);
+	get_online_cpus();
+
+	if (!cpumask_test_cpu(cpu, &osnoise_cpumask))
+		goto out_unlock;
+
+	if (!cpumask_test_cpu(cpu, tr->tracing_cpumask))
+		goto out_unlock;
+
+	start_kthread(cpu);
+
+out_unlock:
+	put_online_cpus();
+	mutex_unlock(&interface_lock);
+out_unlock_trace:
+	mutex_unlock(&trace_types_lock);
+}
+
+static DECLARE_WORK(osnoise_hotplug_work, osnoise_hotplug_workfn);
+
+/*
+ * osnoise_cpu_init - CPU hotplug online callback function
+ */
+static int osnoise_cpu_init(unsigned int cpu)
+{
+	schedule_work_on(cpu, &osnoise_hotplug_work);
+	return 0;
+}
+
+/*
+ * osnoise_cpu_die - CPU hotplug offline callback function
+ */
+static int osnoise_cpu_die(unsigned int cpu)
+{
+	stop_kthread(cpu);
+	return 0;
+}
+
+static void osnoise_init_hotplug_support(void)
+{
+	int ret;
+
+	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "trace/osnoise:online",
+				osnoise_cpu_init, osnoise_cpu_die);
+	if (ret < 0)
+		pr_warn(BANNER "Error to init cpu hotplug support\n");
+
+	return;
+}
+#else /* CONFIG_HOTPLUG_CPU */
+static void osnoise_init_hotplug_support(void)
+{
+	return 0;
+}
+#endif /* CONFIG_HOTPLUG_CPU */
+
 /*
  * osnoise_cpus_read - Read function for reading the "cpus" file
  * @filp: The active open file structure
@@ -1583,7 +1680,14 @@ osnoise_cpus_write(struct file *filp, const char __user *ubuf, size_t count,
 		osnoise_tracer_stop(tr);
 
 	mutex_lock(&interface_lock);
+	/*
+	 * osnoise_cpumask is read by CPU hotplug operations.
+	 */
+	get_online_cpus();
+
 	cpumask_copy(&osnoise_cpumask, osnoise_cpumask_new);
+
+	put_online_cpus();
 	mutex_unlock(&interface_lock);
 
 	if (running)
@@ -1940,6 +2044,7 @@ __init static int init_osnoise_tracer(void)
 		return ret;
 	}
 #endif
+	osnoise_init_hotplug_support();
 
 	init_tracefs();
 
-- 
2.30.2