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OpenCloudOS-Kernel/kernel/trace/trace_hwlat.c

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// SPDX-License-Identifier: GPL-2.0
/*
* trace_hwlat.c - A simple Hardware Latency detector.
*
* Use this tracer to detect large system latencies induced by the behavior of
* certain underlying system hardware or firmware, independent of Linux itself.
* The code was developed originally to detect the presence of SMIs on Intel
* and AMD systems, although there is no dependency upon x86 herein.
*
* The classical example usage of this tracer is in detecting the presence of
* SMIs or System Management Interrupts on Intel and AMD systems. An SMI is a
* somewhat special form of hardware interrupt spawned from earlier CPU debug
* modes in which the (BIOS/EFI/etc.) firmware arranges for the South Bridge
* LPC (or other device) to generate a special interrupt under certain
* circumstances, for example, upon expiration of a special SMI timer device,
* due to certain external thermal readings, on certain I/O address accesses,
* and other situations. An SMI hits a special CPU pin, triggers a special
* SMI mode (complete with special memory map), and the OS is unaware.
*
* Although certain hardware-inducing latencies are necessary (for example,
* a modern system often requires an SMI handler for correct thermal control
* and remote management) they can wreak havoc upon any OS-level performance
* guarantees toward low-latency, especially when the OS is not even made
* aware of the presence of these interrupts. For this reason, we need a
* somewhat brute force mechanism to detect these interrupts. In this case,
* we do it by hogging all of the CPU(s) for configurable timer intervals,
* sampling the built-in CPU timer, looking for discontiguous readings.
*
* WARNING: This implementation necessarily introduces latencies. Therefore,
* you should NEVER use this tracer while running in a production
* environment requiring any kind of low-latency performance
* guarantee(s).
*
* 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 <williams@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 "trace.h"
static struct trace_array *hwlat_trace;
#define U64STR_SIZE 22 /* 20 digits max */
#define BANNER "hwlat_detector: "
#define DEFAULT_SAMPLE_WINDOW 1000000 /* 1s */
#define DEFAULT_SAMPLE_WIDTH 500000 /* 0.5s */
#define DEFAULT_LAT_THRESHOLD 10 /* 10us */
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_PER_CPU,
MODE_MAX
};
static char *thread_mode_str[] = { "none", "round-robin", "per-cpu" };
/* Save the previous tracing_thresh value */
static unsigned long save_tracing_thresh;
/* 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;
/* If the user changed threshold, remember it */
static u64 last_tracing_thresh = DEFAULT_LAT_THRESHOLD * NSEC_PER_USEC;
/* Individual latency samples are stored here when detected. */
struct hwlat_sample {
u64 seqnum; /* unique sequence */
u64 duration; /* delta */
u64 outer_duration; /* delta (outer loop) */
u64 nmi_total_ts; /* Total time spent in NMIs */
struct timespec64 timestamp; /* wall time */
int nmi_count; /* # NMIs during this sample */
int count; /* # of iterations over thresh */
};
/* keep the global state somewhere. */
static struct hwlat_data {
struct mutex lock; /* protect changes */
u64 count; /* total since reset */
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 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)
{
struct trace_array *tr = hwlat_trace;
struct trace_event_call *call = &event_hwlat;
struct trace_buffer *buffer = tr->array_buffer.buffer;
struct ring_buffer_event *event;
struct hwlat_entry *entry;
event = trace_buffer_lock_reserve(buffer, TRACE_HWLAT, sizeof(*entry),
tracing_gen_ctx());
if (!event)
return;
entry = ring_buffer_event_data(event);
entry->seqnum = sample->seqnum;
entry->duration = sample->duration;
entry->outer_duration = sample->outer_duration;
entry->timestamp = sample->timestamp;
entry->nmi_total_ts = sample->nmi_total_ts;
entry->nmi_count = sample->nmi_count;
entry->count = sample->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_type u64
#define time_get() trace_clock_local()
#define time_to_us(x) div_u64(x, 1000)
#define time_sub(a, b) ((a) - (b))
#define init_time(a, b) (a = b)
#define time_u64(a) a
void trace_hwlat_callback(bool enter)
{
struct hwlat_kthread_data *kdata = get_cpu_data();
if (!kdata->kthread)
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)
kdata->nmi_ts_start = time_get();
else
kdata->nmi_total_ts += time_get() - kdata->nmi_ts_start;
}
if (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
*
* Used to repeatedly capture the CPU TSC (or similar), looking for potential
* hardware-induced latency. Called with interrupts disabled and with
* hwlat_data.lock held.
*/
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;
s64 diff, outer_diff, total, last_total = 0;
u64 sample = 0;
u64 thresh = tracing_thresh;
u64 outer_sample = 0;
int ret = -1;
unsigned int count = 0;
do_div(thresh, NSEC_PER_USEC); /* modifies interval value */
kdata->nmi_total_ts = 0;
kdata->nmi_count = 0;
/* Make sure NMIs see this first */
barrier();
trace_hwlat_callback_enabled = true;
init_time(last_t2, 0);
start = time_get(); /* start timestamp */
outer_diff = 0;
do {
t1 = time_get(); /* we'll look for a discontinuity */
t2 = time_get();
if (time_u64(last_t2)) {
/* Check the delta from outer loop (t2 to next t1) */
outer_diff = time_to_us(time_sub(t1, last_t2));
/* This shouldn't happen */
if (outer_diff < 0) {
hwlat_err(BANNER "time running backwards\n");
goto out;
}
if (outer_diff > outer_sample)
outer_sample = outer_diff;
}
last_t2 = t2;
total = time_to_us(time_sub(t2, start)); /* sample width */
/* Check for possible overflows */
if (total < last_total) {
hwlat_err("Time total overflowed\n");
break;
}
last_total = total;
/* This checks the inner loop (t1 to t2) */
diff = time_to_us(time_sub(t2, t1)); /* current diff */
if (diff > thresh || outer_diff > thresh) {
if (!count)
ktime_get_real_ts64(&s.timestamp);
count++;
}
/* This shouldn't happen */
if (diff < 0) {
hwlat_err(BANNER "time running backwards\n");
goto out;
}
if (diff > sample)
sample = diff; /* only want highest value */
} while (total <= hwlat_data.sample_width);
barrier(); /* finish the above in the view for NMIs */
trace_hwlat_callback_enabled = false;
barrier(); /* Make sure nmi_total_ts is no longer updated */
ret = 0;
/* If we exceed the threshold value, we have found a hardware latency */
if (sample > thresh || outer_sample > thresh) {
u64 latency;
ret = 1;
/* We read in microseconds */
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 = kdata->nmi_total_ts;
s.nmi_count = kdata->nmi_count;
s.count = count;
trace_hwlat_sample(&s);
latency = max(sample, outer_sample);
/* Keep a running maximum ever recorded hardware latency */
if (latency > tr->max_latency) {
tr->max_latency = latency;
latency_fsnotify(tr);
}
}
out:
return ret;
}
static struct cpumask save_cpumask;
static void move_to_next_cpu(void)
{
struct cpumask *current_mask = &save_cpumask;
struct trace_array *tr = hwlat_trace;
int next_cpu;
/*
* 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 change_mode;
cpus_read_lock();
cpumask_and(current_mask, cpu_online_mask, tr->tracing_cpumask);
next_cpu = cpumask_next(raw_smp_processor_id(), current_mask);
cpus_read_unlock();
if (next_cpu >= nr_cpu_ids)
next_cpu = cpumask_first(current_mask);
if (next_cpu >= nr_cpu_ids) /* Shouldn't happen! */
goto change_mode;
cpumask_clear(current_mask);
cpumask_set_cpu(next_cpu, current_mask);
sched_setaffinity(0, current_mask);
return;
change_mode:
hwlat_data.thread_mode = MODE_NONE;
pr_info(BANNER "cpumask changed while in round-robin mode, switching to mode none\n");
}
/*
* kthread_fn - The CPU time sampling/hardware latency detection kernel thread
*
* Used to periodically sample the CPU TSC via a call to get_sample. We
* disable interrupts, which does (intentionally) introduce latency since we
* need to ensure nothing else might be running (and thus preempting).
* Obviously this should never be used in production environments.
*
* Executes one loop interaction on each CPU in tracing_cpumask sysfs file.
*/
static int kthread_fn(void *data)
{
u64 interval;
while (!kthread_should_stop()) {
if (hwlat_data.thread_mode == MODE_ROUND_ROBIN)
move_to_next_cpu();
local_irq_disable();
get_sample();
local_irq_enable();
mutex_lock(&hwlat_data.lock);
interval = hwlat_data.sample_window - hwlat_data.sample_width;
mutex_unlock(&hwlat_data.lock);
do_div(interval, USEC_PER_MSEC); /* modifies interval value */
/* Always sleep for at least 1ms */
if (interval < 1)
interval = 1;
if (msleep_interruptible(interval))
break;
}
return 0;
}
/*
* 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;
cpus_read_lock();
kthread = kdata->kthread;
if (!kthread)
goto out_put_cpus;
kthread_stop(kthread);
kdata->kthread = NULL;
out_put_cpus:
cpus_read_unlock();
}
/*
* 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_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;
cpus_read_lock();
if (kdata->kthread)
goto out_put_cpus;
kthread = kthread_create(kthread_fn, NULL, "hwlatd");
if (IS_ERR(kthread)) {
pr_err(BANNER "could not start sampling thread\n");
cpus_read_unlock();
return -ENOMEM;
}
/* Just pick the first CPU on first iteration */
cpumask_and(current_mask, cpu_online_mask, tr->tracing_cpumask);
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);
kdata->kthread = kthread;
wake_up_process(kthread);
out_put_cpus:
cpus_read_unlock();
return 0;
}
/*
* 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);
per_cpu(hwlat_per_cpu_data, cpu).kthread = NULL;
}
/*
* stop_per_cpu_kthreads - Inform the hardware latency sampling/detector kthread to stop
*
* 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_per_cpu_kthreads(void)
{
unsigned int cpu;
cpus_read_lock();
for_each_online_cpu(cpu)
stop_cpu_kthread(cpu);
cpus_read_unlock();
}
/*
* 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;
}
#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);
cpus_read_lock();
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:
cpus_read_unlock();
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
*
* 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;
cpus_read_lock();
/*
* 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;
}
cpus_read_unlock();
return 0;
out_error:
cpus_read_unlock();
stop_per_cpu_kthreads();
return retval;
}
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. 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)
{
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;
}
/*
* 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,
};
/*
* 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 = {
.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
*
* This function creates entries in tracefs for "hwlat_detector".
* It creates the hwlat_detector directory in the tracing directory,
* and within that directory is the count, width and window files to
* change and view those values.
*/
static int init_tracefs(void)
{
int ret;
struct dentry *top_dir;
ret = tracing_init_dentry();
if (ret)
return -ENOMEM;
top_dir = tracefs_create_dir("hwlat_detector", NULL);
if (!top_dir)
return -ENOMEM;
hwlat_sample_window = tracefs_create_file("window", TRACE_MODE_WRITE,
top_dir,
&hwlat_window,
&trace_min_max_fops);
if (!hwlat_sample_window)
goto err;
hwlat_sample_width = tracefs_create_file("width", TRACE_MODE_WRITE,
top_dir,
&hwlat_width,
&trace_min_max_fops);
if (!hwlat_sample_width)
goto err;
hwlat_thread_mode = trace_create_file("mode", TRACE_MODE_WRITE,
top_dir,
NULL,
&thread_mode_fops);
if (!hwlat_thread_mode)
goto err;
return 0;
err:
tracefs_remove(top_dir);
return -ENOMEM;
}
static void hwlat_tracer_start(struct trace_array *tr)
{
int err;
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)
{
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)
{
/* Only allow one instance to enable this */
if (hwlat_busy)
return -EBUSY;
hwlat_trace = tr;
hwlat_data.count = 0;
tr->max_latency = 0;
save_tracing_thresh = tracing_thresh;
/* tracing_thresh is in nsecs, we speak in usecs */
if (!tracing_thresh)
tracing_thresh = last_tracing_thresh;
if (tracer_tracing_is_on(tr))
hwlat_tracer_start(tr);
hwlat_busy = true;
return 0;
}
static void hwlat_tracer_reset(struct trace_array *tr)
{
hwlat_tracer_stop(tr);
/* the tracing threshold is static between runs */
last_tracing_thresh = tracing_thresh;
tracing_thresh = save_tracing_thresh;
hwlat_busy = false;
}
static struct tracer hwlat_tracer __read_mostly =
{
.name = "hwlat",
.init = hwlat_tracer_init,
.reset = hwlat_tracer_reset,
.start = hwlat_tracer_start,
.stop = hwlat_tracer_stop,
.allow_instances = true,
};
__init static int init_hwlat_tracer(void)
{
int ret;
mutex_init(&hwlat_data.lock);
ret = register_tracer(&hwlat_tracer);
if (ret)
return ret;
hwlat_init_hotplug_support();
init_tracefs();
return 0;
}
late_initcall(init_hwlat_tracer);
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