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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. <[email protected]>
- * Copyright (C) 2013-2016 Steven Rostedt, Red Hat, Inc. <[email protected]>
- *
- * Includes useful feedback from Clark Williams <[email protected]>
- *
- */
- #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);
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