Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2442 insertions, 0 deletions

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
new file mode 100644
index 000000000..26111b0ca
--- /dev/null
+++ b/kernel/trace/trace_osnoise.c
@@ -0,0 +1,2442 @@
+// 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>
+ *   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 <uapi/linux/sched/types.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>
+
+/*
+ * Default values.
+ */
+#define BANNER			"osnoise: "
+#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 */
+
+/*
+ * trace_array of the enabled osnoise/timerlat instances.
+ */
+struct osnoise_instance {
+	struct list_head	list;
+	struct trace_array	*tr;
+};
+
+static struct list_head osnoise_instances;
+
+static bool osnoise_has_registered_instances(void)
+{
+	return !!list_first_or_null_rcu(&osnoise_instances,
+					struct osnoise_instance,
+					list);
+}
+
+/*
+ * osnoise_instance_registered - check if a tr is already registered
+ */
+static int osnoise_instance_registered(struct trace_array *tr)
+{
+	struct osnoise_instance *inst;
+	int found = 0;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(inst, &osnoise_instances, list) {
+		if (inst->tr == tr)
+			found = 1;
+	}
+	rcu_read_unlock();
+
+	return found;
+}
+
+/*
+ * osnoise_register_instance - register a new trace instance
+ *
+ * Register a trace_array *tr in the list of instances running
+ * osnoise/timerlat tracers.
+ */
+static int osnoise_register_instance(struct trace_array *tr)
+{
+	struct osnoise_instance *inst;
+
+	/*
+	 * register/unregister serialization is provided by trace's
+	 * trace_types_lock.
+	 */
+	lockdep_assert_held(&trace_types_lock);
+
+	inst = kmalloc(sizeof(*inst), GFP_KERNEL);
+	if (!inst)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD_RCU(&inst->list);
+	inst->tr = tr;
+	list_add_tail_rcu(&inst->list, &osnoise_instances);
+
+	return 0;
+}
+
+/*
+ *  osnoise_unregister_instance - unregister a registered trace instance
+ *
+ * Remove the trace_array *tr from the list of instances running
+ * osnoise/timerlat tracers.
+ */
+static void osnoise_unregister_instance(struct trace_array *tr)
+{
+	struct osnoise_instance *inst;
+	int found = 0;
+
+	/*
+	 * register/unregister serialization is provided by trace's
+	 * trace_types_lock.
+	 */
+	list_for_each_entry_rcu(inst, &osnoise_instances, list,
+				lockdep_is_held(&trace_types_lock)) {
+		if (inst->tr == tr) {
+			list_del_rcu(&inst->list);
+			found = 1;
+			break;
+		}
+	}
+
+	if (!found)
+		return;
+
+	kvfree_rcu(inst);
+}
+
+/*
+ * 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;
+};
+
+#define IRQ_CONTEXT	0
+#define THREAD_CONTEXT	1
+/*
+ * 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);
+}
+
+#ifdef CONFIG_TIMERLAT_TRACER
+/*
+ * 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 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.
+	 */
+	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 - Reset the values of the given osnoise_variables
+ */
+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);
+		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.
+ */
+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 */
+};
+
+#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.
+ */
+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 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
+};
+
+#ifdef CONFIG_TIMERLAT_TRACER
+static inline bool timerlat_enabled(void)
+{
+	return osnoise_data.timerlat_tracer;
+}
+
+static inline int timerlat_softirq_exit(struct osnoise_variables *osn_var)
+{
+	struct timerlat_variables *tlat_var = this_cpu_tmr_var();
+	/*
+	 * If the timerlat is enabled, but the irq handler did
+	 * not run yet enabling timerlat_tracer, do not trace.
+	 */
+	if (!tlat_var->tracing_thread) {
+		osn_var->softirq.arrival_time = 0;
+		osn_var->softirq.delta_start = 0;
+		return 0;
+	}
+	return 1;
+}
+
+static inline int timerlat_thread_exit(struct osnoise_variables *osn_var)
+{
+	struct timerlat_variables *tlat_var = this_cpu_tmr_var();
+	/*
+	 * If the timerlat is enabled, but the irq handler did
+	 * not run yet enabling timerlat_tracer, do not trace.
+	 */
+	if (!tlat_var->tracing_thread) {
+		osn_var->thread.delta_start = 0;
+		osn_var->thread.arrival_time = 0;
+		return 0;
+	}
+	return 1;
+}
+#else /* CONFIG_TIMERLAT_TRACER */
+static inline bool timerlat_enabled(void)
+{
+	return false;
+}
+
+static inline int timerlat_softirq_exit(struct osnoise_variables *osn_var)
+{
+	return 1;
+}
+static inline int timerlat_thread_exit(struct osnoise_variables *osn_var)
+{
+	return 1;
+}
+#endif
+
+#ifdef CONFIG_PREEMPT_RT
+/*
+ * 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, "#                              | / _-----=> need-resched-lazy\n");
+	seq_puts(s, "#                              || / _----=> hardirq/softirq\n");
+	seq_puts(s, "#                              ||| / _---=> preempt-depth\n");
+	seq_puts(s, "#                              |||| / _--=> preempt-lazy-depth\n");
+	seq_puts(s, "#                              ||||| / _-=> migrate-disable\n");
+
+	seq_puts(s, "#                              |||||| /          ");
+	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");
+}
+#else /* CONFIG_PREEMPT_RT */
+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\n");
+	seq_puts(s, "#                              ||| / _-=> migrate-disable     ");
+	seq_puts(s, "                    MAX\n");
+	seq_puts(s, "#                              |||| /     delay               ");
+	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");
+}
+#endif /* CONFIG_PREEMPT_RT */
+
+/*
+ * osnoise_taint - report an osnoise error.
+ */
+#define osnoise_taint(msg) ({							\
+	struct osnoise_instance *inst;						\
+	struct trace_buffer *buffer;						\
+										\
+	rcu_read_lock();							\
+	list_for_each_entry_rcu(inst, &osnoise_instances, list) {		\
+		buffer = inst->tr->array_buffer.buffer;				\
+		trace_array_printk_buf(buffer, _THIS_IP_, msg);			\
+	}									\
+	rcu_read_unlock();							\
+	osnoise_data.tainted = true;						\
+})
+
+/*
+ * Record an osnoise_sample into the tracer buffer.
+ */
+static void
+__trace_osnoise_sample(struct osnoise_sample *sample, struct trace_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);
+}
+
+/*
+ * Record an osnoise_sample on all osnoise instances.
+ */
+static void trace_osnoise_sample(struct osnoise_sample *sample)
+{
+	struct osnoise_instance *inst;
+	struct trace_buffer *buffer;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(inst, &osnoise_instances, list) {
+		buffer = inst->tr->array_buffer.buffer;
+		__trace_osnoise_sample(sample, buffer);
+	}
+	rcu_read_unlock();
+}
+
+#ifdef CONFIG_TIMERLAT_TRACER
+/*
+ * Print the timerlat header info.
+ */
+#ifdef CONFIG_PREEMPT_RT
+static void print_timerlat_headers(struct seq_file *s)
+{
+	seq_puts(s, "#                                _-------=> irqs-off\n");
+	seq_puts(s, "#                               / _------=> need-resched\n");
+	seq_puts(s, "#                              | / _-----=> need-resched-lazy\n");
+	seq_puts(s, "#                              || / _----=> hardirq/softirq\n");
+	seq_puts(s, "#                              ||| / _---=> preempt-depth\n");
+	seq_puts(s, "#                              |||| / _--=> preempt-lazy-depth\n");
+	seq_puts(s, "#                              ||||| / _-=> migrate-disable\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");
+}
+#else /* CONFIG_PREEMPT_RT */
+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, "#                              ||| / _-=> migrate-disable\n");
+	seq_puts(s, "#                              |||| /     delay\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");
+}
+#endif /* CONFIG_PREEMPT_RT */
+
+static void
+__trace_timerlat_sample(struct timerlat_sample *sample, struct trace_buffer *buffer)
+{
+	struct trace_event_call *call = &event_osnoise;
+	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);
+}
+
+/*
+ * Record an timerlat_sample into the tracer buffer.
+ */
+static void trace_timerlat_sample(struct timerlat_sample *sample)
+{
+	struct osnoise_instance *inst;
+	struct trace_buffer *buffer;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(inst, &osnoise_instances, list) {
+		buffer = inst->tr->array_buffer.buffer;
+		__trace_timerlat_sample(sample, buffer);
+	}
+	rcu_read_unlock();
+}
+
+#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;
+
+}
+
+static void
+__timerlat_dump_stack(struct trace_buffer *buffer, struct trace_stack *fstack, unsigned int size)
+{
+	struct trace_event_call *call = &event_osnoise;
+	struct ring_buffer_event *event;
+	struct stack_entry *entry;
+
+	event = trace_buffer_lock_reserve(buffer, TRACE_STACK, sizeof(*entry) + size,
+					  tracing_gen_ctx());
+	if (!event)
+		return;
+
+	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);
+}
+
+/*
+ * timerlat_dump_stack - dump a stack trace previously saved
+ */
+static void timerlat_dump_stack(u64 latency)
+{
+	struct osnoise_instance *inst;
+	struct trace_buffer *buffer;
+	struct trace_stack *fstack;
+	unsigned int size;
+
+	/*
+	 * trace only if latency > print_stack config, if enabled.
+	 */
+	if (!osnoise_data.print_stack || osnoise_data.print_stack > latency)
+		return;
+
+	preempt_disable_notrace();
+	fstack = this_cpu_ptr(&trace_stack);
+	size = fstack->stack_size;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(inst, &osnoise_instances, list) {
+		buffer = inst->tr->array_buffer.buffer;
+		__timerlat_dump_stack(buffer, fstack, size);
+
+	}
+	rcu_read_unlock();
+	preempt_enable_notrace();
+}
+#else /* CONFIG_STACKTRACE */
+#define timerlat_dump_stack(u64 latency) 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.
+ */
+#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;
+}
+
+#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
+ *
+ * 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();
+	s64 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.
+ */
+static 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.
+ */
+static 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().
+ */
+static 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.
+ */
+static void trace_softirq_exit_callback(void *data, unsigned int vec_nr)
+{
+	struct osnoise_variables *osn_var = this_cpu_osn_var();
+	s64 duration;
+
+	if (!osn_var->sampling)
+		return;
+
+	if (unlikely(timerlat_enabled()))
+		if (!timerlat_softirq_exit(osn_var))
+			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)
+{
+	s64 duration;
+
+	if (!osn_var->sampling)
+		return;
+
+	if (unlikely(timerlat_enabled()))
+		if (!timerlat_thread_exit(osn_var))
+			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.
+ */
+static void
+trace_sched_switch_callback(void *data, bool preempt,
+			    struct task_struct *p,
+			    struct task_struct *n,
+			    unsigned int prev_state)
+{
+	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.
+ */
+static 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.
+ */
+static 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.
+ */
+static 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.
+ */
+static 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 __always_inline void osnoise_stop_tracing(void)
+{
+	struct osnoise_instance *inst;
+	struct trace_array *tr;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(inst, &osnoise_instances, list) {
+		tr = inst->tr;
+		trace_array_printk_buf(tr->array_buffer.buffer, _THIS_IP_,
+				"stop tracing hit on cpu %d\n", smp_processor_id());
+
+		tracer_tracing_off(tr);
+	}
+	rcu_read_unlock();
+}
+
+/*
+ * notify_new_max_latency - Notify a new max latency via fsnotify interface.
+ */
+static void notify_new_max_latency(u64 latency)
+{
+	struct osnoise_instance *inst;
+	struct trace_array *tr;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(inst, &osnoise_instances, list) {
+		tr = inst->tr;
+		if (tracer_tracing_is_on(tr) && tr->max_latency < latency) {
+			tr->max_latency = latency;
+			latency_fsnotify(tr);
+		}
+	}
+	rcu_read_unlock();
+}
+
+/*
+ * 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 start, sample, last_sample;
+	u64 last_int_count, int_count;
+	s64 noise = 0, max_noise = 0;
+	s64 total, last_total = 0;
+	struct osnoise_sample s;
+	unsigned int threshold;
+	u64 runtime, stop_in;
+	u64 sum_noise = 0;
+	int hw_count = 0;
+	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();
+		}
+
+		/*
+		 * In some cases, notably when running on a nohz_full CPU with
+		 * a stopped tick PREEMPT_RCU has no way to account for QSs.
+		 * This will eventually cause unwarranted noise as PREEMPT_RCU
+		 * will force preemption as the means of ending the current
+		 * grace period. We avoid this problem by calling
+		 * rcu_momentary_dyntick_idle(), which performs a zero duration
+		 * EQS allowing PREEMPT_RCU to end the current grace period.
+		 * This call shouldn't be wrapped inside an RCU critical
+		 * section.
+		 *
+		 * Note that in non PREEMPT_RCU kernels QSs are handled through
+		 * cond_resched()
+		 */
+		if (IS_ENABLED(CONFIG_PREEMPT_RCU)) {
+			local_irq_disable();
+			rcu_momentary_dyntick_idle();
+			local_irq_enable();
+		}
+
+		/*
+		 * 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);
+
+	notify_new_max_latency(max_noise);
+
+	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_sleep - sleep until the next period
+ */
+static void osnoise_sleep(void)
+{
+	u64 interval;
+	ktime_t wake_time;
+
+	mutex_lock(&interface_lock);
+	interval = osnoise_data.sample_period - osnoise_data.sample_runtime;
+	mutex_unlock(&interface_lock);
+
+	/*
+	 * differently from hwlat_detector, the osnoise tracer can run
+	 * without a pause because preemption is on.
+	 */
+	if (!interval) {
+		/* Let synchronize_rcu_tasks() make progress */
+		cond_resched_tasks_rcu_qs();
+		return;
+	}
+
+	wake_time = ktime_add_us(ktime_get(), interval);
+	__set_current_state(TASK_INTERRUPTIBLE);
+
+	while (schedule_hrtimeout_range(&wake_time, 0, HRTIMER_MODE_ABS)) {
+		if (kthread_should_stop())
+			break;
+	}
+}
+
+/*
+ * 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)
+{
+
+	while (!kthread_should_stop()) {
+		run_osnoise();
+		osnoise_sleep();
+	}
+
+	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 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.
+	 *
+	 * The PREEMPT_RT is a special case, though. As softirqs run as threads
+	 * on RT, moving the thread is enough.
+	 */
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT) && 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);
+	}
+
+	/*
+	 * 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);
+
+	if (osnoise_data.stop_tracing) {
+		if (time_to_us(diff) >= osnoise_data.stop_tracing) {
+
+			/*
+			 * At this point, if stop_tracing is set and <= print_stack,
+			 * print_stack is set and would be printed in the thread handler.
+			 *
+			 * Thus, print the stack trace as it is helpful to define the
+			 * root cause of an IRQ latency.
+			 */
+			if (osnoise_data.stop_tracing <= osnoise_data.print_stack) {
+				timerlat_save_stack(0);
+				timerlat_dump_stack(time_to_us(diff));
+			}
+
+			osnoise_stop_tracing();
+			notify_new_max_latency(diff);
+
+			wake_up_process(tlat->kthread);
+
+			return HRTIMER_NORESTART;
+		}
+	}
+
+	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);
+
+		notify_new_max_latency(diff);
+
+		timerlat_dump_stack(time_to_us(diff));
+
+		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;
+}
+#else /* CONFIG_TIMERLAT_TRACER */
+static int timerlat_main(void *data)
+{
+	return 0;
+}
+#endif /* CONFIG_TIMERLAT_TRACER */
+
+/*
+ * 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)
+{
+	int cpu;
+
+	cpus_read_lock();
+
+	for_each_online_cpu(cpu)
+		stop_kthread(cpu);
+
+	cpus_read_unlock();
+}
+
+/*
+ * start_kthread - Start a workload tread
+ */
+static int start_kthread(unsigned int cpu)
+{
+	struct task_struct *kthread;
+	void *main = osnoise_main;
+	char comm[24];
+
+	if (timerlat_enabled()) {
+		snprintf(comm, 24, "timerlat/%d", cpu);
+		main = timerlat_main;
+	} else {
+		snprintf(comm, 24, "osnoise/%d", cpu);
+	}
+
+	kthread = kthread_run_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;
+
+	return 0;
+}
+
+/*
+ * 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(void)
+{
+	struct cpumask *current_mask = &save_cpumask;
+	int retval = 0;
+	int cpu;
+
+	cpus_read_lock();
+	/*
+	 * Run only on online CPUs in which osnoise is allowed to run.
+	 */
+	cpumask_and(current_mask, cpu_online_mask, &osnoise_cpumask);
+
+	for_each_possible_cpu(cpu)
+		per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;
+
+	for_each_cpu(cpu, current_mask) {
+		retval = start_kthread(cpu);
+		if (retval) {
+			cpus_read_unlock();
+			stop_per_cpu_kthreads();
+			return retval;
+		}
+	}
+
+	cpus_read_unlock();
+
+	return retval;
+}
+
+#ifdef CONFIG_HOTPLUG_CPU
+static void osnoise_hotplug_workfn(struct work_struct *dummy)
+{
+	unsigned int cpu = smp_processor_id();
+
+	mutex_lock(&trace_types_lock);
+
+	if (!osnoise_has_registered_instances())
+		goto out_unlock_trace;
+
+	mutex_lock(&interface_lock);
+	cpus_read_lock();
+
+	if (!cpumask_test_cpu(cpu, &osnoise_cpumask))
+		goto out_unlock;
+
+	start_kthread(cpu);
+
+out_unlock:
+	cpus_read_unlock();
+	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;
+}
+#endif /* CONFIG_HOTPLUG_CPU */
+
+/*
+ * 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;
+}
+
+/*
+ * 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. Why not use "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)
+{
+	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.
+	 */
+	mutex_lock(&trace_types_lock);
+	running = osnoise_has_registered_instances();
+	if (running)
+		stop_per_cpu_kthreads();
+
+	mutex_lock(&interface_lock);
+	/*
+	 * osnoise_cpumask is read by CPU hotplug operations.
+	 */
+	cpus_read_lock();
+
+	cpumask_copy(&osnoise_cpumask, osnoise_cpumask_new);
+
+	cpus_read_unlock();
+	mutex_unlock(&interface_lock);
+
+	if (running)
+		start_per_cpu_kthreads();
+	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,
+};
+
+#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,
+	.write		= osnoise_cpus_write,
+	.llseek		= generic_file_llseek,
+};
+
+#ifdef CONFIG_TIMERLAT_TRACER
+#ifdef CONFIG_STACKTRACE
+static int init_timerlat_stack_tracefs(struct dentry *top_dir)
+{
+	struct dentry *tmp;
+
+	tmp = tracefs_create_file("print_stack", TRACE_MODE_WRITE, top_dir,
+				  &osnoise_print_stack, &trace_min_max_fops);
+	if (!tmp)
+		return -ENOMEM;
+
+	return 0;
+}
+#else /* CONFIG_STACKTRACE */
+static int init_timerlat_stack_tracefs(struct dentry *top_dir)
+{
+	return 0;
+}
+#endif /* CONFIG_STACKTRACE */
+
+/*
+ * init_timerlat_tracefs - A function to initialize the timerlat interface files
+ */
+static int init_timerlat_tracefs(struct dentry *top_dir)
+{
+	struct dentry *tmp;
+
+	tmp = tracefs_create_file("timerlat_period_us", TRACE_MODE_WRITE, top_dir,
+				  &timerlat_period, &trace_min_max_fops);
+	if (!tmp)
+		return -ENOMEM;
+
+	return init_timerlat_stack_tracefs(top_dir);
+}
+#else /* CONFIG_TIMERLAT_TRACER */
+static int init_timerlat_tracefs(struct dentry *top_dir)
+{
+	return 0;
+}
+#endif /* CONFIG_TIMERLAT_TRACER */
+
+/*
+ * init_tracefs - A function to initialize the tracefs interface files
+ *
+ * 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)
+{
+	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 0;
+
+	tmp = tracefs_create_file("period_us", TRACE_MODE_WRITE, top_dir,
+				  &osnoise_period, &trace_min_max_fops);
+	if (!tmp)
+		goto err;
+
+	tmp = tracefs_create_file("runtime_us", TRACE_MODE_WRITE, top_dir,
+				  &osnoise_runtime, &trace_min_max_fops);
+	if (!tmp)
+		goto err;
+
+	tmp = tracefs_create_file("stop_tracing_us", TRACE_MODE_WRITE, top_dir,
+				  &osnoise_stop_tracing_in, &trace_min_max_fops);
+	if (!tmp)
+		goto err;
+
+	tmp = tracefs_create_file("stop_tracing_total_us", TRACE_MODE_WRITE, top_dir,
+				  &osnoise_stop_tracing_total, &trace_min_max_fops);
+	if (!tmp)
+		goto err;
+
+	tmp = trace_create_file("cpus", TRACE_MODE_WRITE, top_dir, NULL, &cpus_fops);
+	if (!tmp)
+		goto err;
+
+	ret = init_timerlat_tracefs(top_dir);
+	if (ret)
+		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_unhook_events(void)
+{
+	unhook_thread_events();
+	unhook_softirq_events();
+	unhook_irq_events();
+}
+
+/*
+ * osnoise_workload_start - start the workload and hook to events
+ */
+static int osnoise_workload_start(void)
+{
+	int retval;
+
+	/*
+	 * Instances need to be registered after calling workload
+	 * start. Hence, if there is already an instance, the
+	 * workload was already registered. Otherwise, this
+	 * code is on the way to register the first instance,
+	 * and the workload will start.
+	 */
+	if (osnoise_has_registered_instances())
+		return 0;
+
+	osn_var_reset_all();
+
+	retval = osnoise_hook_events();
+	if (retval)
+		return retval;
+
+	/*
+	 * Make sure that ftrace_nmi_enter/exit() see reset values
+	 * before enabling trace_osnoise_callback_enabled.
+	 */
+	barrier();
+	trace_osnoise_callback_enabled = true;
+
+	retval = start_per_cpu_kthreads();
+	if (retval) {
+		trace_osnoise_callback_enabled = false;
+		/*
+		 * Make sure that ftrace_nmi_enter/exit() see
+		 * trace_osnoise_callback_enabled as false before continuing.
+		 */
+		barrier();
+
+		osnoise_unhook_events();
+		return retval;
+	}
+
+	return 0;
+}
+
+/*
+ * osnoise_workload_stop - stop the workload and unhook the events
+ */
+static void osnoise_workload_stop(void)
+{
+	/*
+	 * Instances need to be unregistered before calling
+	 * stop. Hence, if there is a registered instance, more
+	 * than one instance is running, and the workload will not
+	 * yet stop. Otherwise, this code is on the way to disable
+	 * the last instance, and the workload can stop.
+	 */
+	if (osnoise_has_registered_instances())
+		return;
+
+	/*
+	 * If callbacks were already disabled in a previous stop
+	 * call, there is no need to disable then again.
+	 *
+	 * For instance, this happens when tracing is stopped via:
+	 * echo 0 > tracing_on
+	 * echo nop > current_tracer.
+	 */
+	if (!trace_osnoise_callback_enabled)
+		return;
+
+	trace_osnoise_callback_enabled = false;
+	/*
+	 * Make sure that ftrace_nmi_enter/exit() see
+	 * trace_osnoise_callback_enabled as false before continuing.
+	 */
+	barrier();
+
+	stop_per_cpu_kthreads();
+
+	osnoise_unhook_events();
+}
+
+static void osnoise_tracer_start(struct trace_array *tr)
+{
+	int retval;
+
+	/*
+	 * If the instance is already registered, there is no need to
+	 * register it again.
+	 */
+	if (osnoise_instance_registered(tr))
+		return;
+
+	retval = osnoise_workload_start();
+	if (retval)
+		pr_err(BANNER "Error starting osnoise tracer\n");
+
+	osnoise_register_instance(tr);
+}
+
+static void osnoise_tracer_stop(struct trace_array *tr)
+{
+	osnoise_unregister_instance(tr);
+	osnoise_workload_stop();
+}
+
+static int osnoise_tracer_init(struct trace_array *tr)
+{
+	/*
+	 * Only allow osnoise tracer if timerlat tracer is not running
+	 * already.
+	 */
+	if (timerlat_enabled())
+		return -EBUSY;
+
+	tr->max_latency = 0;
+
+	osnoise_tracer_start(tr);
+	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,
+};
+
+#ifdef CONFIG_TIMERLAT_TRACER
+static void timerlat_tracer_start(struct trace_array *tr)
+{
+	int retval;
+
+	/*
+	 * If the instance is already registered, there is no need to
+	 * register it again.
+	 */
+	if (osnoise_instance_registered(tr))
+		return;
+
+	retval = osnoise_workload_start();
+	if (retval)
+		pr_err(BANNER "Error starting timerlat tracer\n");
+
+	osnoise_register_instance(tr);
+
+	return;
+}
+
+static void timerlat_tracer_stop(struct trace_array *tr)
+{
+	int cpu;
+
+	osnoise_unregister_instance(tr);
+
+	/*
+	 * Instruct the threads to stop only if this is the last instance.
+	 */
+	if (!osnoise_has_registered_instances()) {
+		for_each_online_cpu(cpu)
+			per_cpu(per_cpu_osnoise_var, cpu).sampling = 0;
+	}
+
+	osnoise_workload_stop();
+}
+
+static int timerlat_tracer_init(struct trace_array *tr)
+{
+	/*
+	 * Only allow timerlat tracer if osnoise tracer is not running already.
+	 */
+	if (osnoise_has_registered_instances() && !osnoise_data.timerlat_tracer)
+		return -EBUSY;
+
+	/*
+	 * If this is the first instance, set timerlat_tracer to block
+	 * osnoise tracer start.
+	 */
+	if (!osnoise_has_registered_instances())
+		osnoise_data.timerlat_tracer = 1;
+
+	tr->max_latency = 0;
+	timerlat_tracer_start(tr);
+
+	return 0;
+}
+
+static void timerlat_tracer_reset(struct trace_array *tr)
+{
+	timerlat_tracer_stop(tr);
+
+	/*
+	 * If this is the last instance, reset timerlat_tracer allowing
+	 * osnoise to be started.
+	 */
+	if (!osnoise_has_registered_instances())
+		osnoise_data.timerlat_tracer = 0;
+}
+
+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,
+};
+
+__init static int init_timerlat_tracer(void)
+{
+	return register_tracer(&timerlat_tracer);
+}
+#else /* CONFIG_TIMERLAT_TRACER */
+__init static int init_timerlat_tracer(void)
+{
+	return 0;
+}
+#endif /* CONFIG_TIMERLAT_TRACER */
+
+__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) {
+		pr_err(BANNER "Error registering osnoise!\n");
+		return ret;
+	}
+
+	ret = init_timerlat_tracer();
+	if (ret) {
+		pr_err(BANNER "Error registering timerlat!\n");
+		return ret;
+	}
+
+	osnoise_init_hotplug_support();
+
+	INIT_LIST_HEAD_RCU(&osnoise_instances);
+
+	init_tracefs();
+
+	return 0;
+}
+late_initcall(init_osnoise_tracer);