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-rw-r--r--kernel/trace/trace_hwlat.c891
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diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
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+++ b/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;
+};
+
+static struct hwlat_kthread_data hwlat_single_cpu_data;
+static 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);
+
+ set_cpus_allowed_ptr(current, 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);
+
+ }
+
+ set_cpus_allowed_ptr(kthread, 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;
+
+ /* Do not start a new hwlatd thread if it is already running */
+ if (per_cpu(hwlat_per_cpu_data, cpu).kthread)
+ return 0;
+
+ kthread = kthread_run_on_cpu(kthread_fn, NULL, cpu, "hwlatd/%u");
+ if (IS_ERR(kthread)) {
+ pr_err(BANNER "could not start sampling thread\n");
+ return -ENOMEM;
+ }
+
+ per_cpu(hwlat_per_cpu_data, cpu).kthread = 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_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 - 1) /* if mode is any but last */
+ 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);