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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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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 */
atomic64_t 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_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;
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. */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 sample_width = READ_ONCE(hwlat_data.sample_width); 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 <= 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);
s.seqnum = atomic64_inc_return(&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_wrap(raw_smp_processor_id(), current_mask); cpus_read_unlock();
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_CPUstatic 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 (!cpu_online(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;
atomic64_set(&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);