drm/panfrost: Remove set but not used variable 'bo'
[linux/fpc-iii.git] / kernel / trace / trace_hwlat.c
bloba48808c4324917cb150f749a85b3474a57e23d83
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * trace_hwlat.c - A simple Hardware Latency detector.
5 * Use this tracer to detect large system latencies induced by the behavior of
6 * certain underlying system hardware or firmware, independent of Linux itself.
7 * The code was developed originally to detect the presence of SMIs on Intel
8 * and AMD systems, although there is no dependency upon x86 herein.
10 * The classical example usage of this tracer is in detecting the presence of
11 * SMIs or System Management Interrupts on Intel and AMD systems. An SMI is a
12 * somewhat special form of hardware interrupt spawned from earlier CPU debug
13 * modes in which the (BIOS/EFI/etc.) firmware arranges for the South Bridge
14 * LPC (or other device) to generate a special interrupt under certain
15 * circumstances, for example, upon expiration of a special SMI timer device,
16 * due to certain external thermal readings, on certain I/O address accesses,
17 * and other situations. An SMI hits a special CPU pin, triggers a special
18 * SMI mode (complete with special memory map), and the OS is unaware.
20 * Although certain hardware-inducing latencies are necessary (for example,
21 * a modern system often requires an SMI handler for correct thermal control
22 * and remote management) they can wreak havoc upon any OS-level performance
23 * guarantees toward low-latency, especially when the OS is not even made
24 * aware of the presence of these interrupts. For this reason, we need a
25 * somewhat brute force mechanism to detect these interrupts. In this case,
26 * we do it by hogging all of the CPU(s) for configurable timer intervals,
27 * sampling the built-in CPU timer, looking for discontiguous readings.
29 * WARNING: This implementation necessarily introduces latencies. Therefore,
30 * you should NEVER use this tracer while running in a production
31 * environment requiring any kind of low-latency performance
32 * guarantee(s).
34 * Copyright (C) 2008-2009 Jon Masters, Red Hat, Inc. <jcm@redhat.com>
35 * Copyright (C) 2013-2016 Steven Rostedt, Red Hat, Inc. <srostedt@redhat.com>
37 * Includes useful feedback from Clark Williams <clark@redhat.com>
40 #include <linux/kthread.h>
41 #include <linux/tracefs.h>
42 #include <linux/uaccess.h>
43 #include <linux/cpumask.h>
44 #include <linux/delay.h>
45 #include <linux/sched/clock.h>
46 #include "trace.h"
48 static struct trace_array *hwlat_trace;
50 #define U64STR_SIZE 22 /* 20 digits max */
52 #define BANNER "hwlat_detector: "
53 #define DEFAULT_SAMPLE_WINDOW 1000000 /* 1s */
54 #define DEFAULT_SAMPLE_WIDTH 500000 /* 0.5s */
55 #define DEFAULT_LAT_THRESHOLD 10 /* 10us */
57 /* sampling thread*/
58 static struct task_struct *hwlat_kthread;
60 static struct dentry *hwlat_sample_width; /* sample width us */
61 static struct dentry *hwlat_sample_window; /* sample window us */
63 /* Save the previous tracing_thresh value */
64 static unsigned long save_tracing_thresh;
66 /* NMI timestamp counters */
67 static u64 nmi_ts_start;
68 static u64 nmi_total_ts;
69 static int nmi_count;
70 static int nmi_cpu;
72 /* Tells NMIs to call back to the hwlat tracer to record timestamps */
73 bool trace_hwlat_callback_enabled;
75 /* If the user changed threshold, remember it */
76 static u64 last_tracing_thresh = DEFAULT_LAT_THRESHOLD * NSEC_PER_USEC;
78 /* Individual latency samples are stored here when detected. */
79 struct hwlat_sample {
80 u64 seqnum; /* unique sequence */
81 u64 duration; /* delta */
82 u64 outer_duration; /* delta (outer loop) */
83 u64 nmi_total_ts; /* Total time spent in NMIs */
84 struct timespec64 timestamp; /* wall time */
85 int nmi_count; /* # NMIs during this sample */
88 /* keep the global state somewhere. */
89 static struct hwlat_data {
91 struct mutex lock; /* protect changes */
93 u64 count; /* total since reset */
95 u64 sample_window; /* total sampling window (on+off) */
96 u64 sample_width; /* active sampling portion of window */
98 } hwlat_data = {
99 .sample_window = DEFAULT_SAMPLE_WINDOW,
100 .sample_width = DEFAULT_SAMPLE_WIDTH,
103 static void trace_hwlat_sample(struct hwlat_sample *sample)
105 struct trace_array *tr = hwlat_trace;
106 struct trace_event_call *call = &event_hwlat;
107 struct trace_buffer *buffer = tr->array_buffer.buffer;
108 struct ring_buffer_event *event;
109 struct hwlat_entry *entry;
110 unsigned long flags;
111 int pc;
113 pc = preempt_count();
114 local_save_flags(flags);
116 event = trace_buffer_lock_reserve(buffer, TRACE_HWLAT, sizeof(*entry),
117 flags, pc);
118 if (!event)
119 return;
120 entry = ring_buffer_event_data(event);
121 entry->seqnum = sample->seqnum;
122 entry->duration = sample->duration;
123 entry->outer_duration = sample->outer_duration;
124 entry->timestamp = sample->timestamp;
125 entry->nmi_total_ts = sample->nmi_total_ts;
126 entry->nmi_count = sample->nmi_count;
128 if (!call_filter_check_discard(call, entry, buffer, event))
129 trace_buffer_unlock_commit_nostack(buffer, event);
132 /* Macros to encapsulate the time capturing infrastructure */
133 #define time_type u64
134 #define time_get() trace_clock_local()
135 #define time_to_us(x) div_u64(x, 1000)
136 #define time_sub(a, b) ((a) - (b))
137 #define init_time(a, b) (a = b)
138 #define time_u64(a) a
140 void trace_hwlat_callback(bool enter)
142 if (smp_processor_id() != nmi_cpu)
143 return;
146 * Currently trace_clock_local() calls sched_clock() and the
147 * generic version is not NMI safe.
149 if (!IS_ENABLED(CONFIG_GENERIC_SCHED_CLOCK)) {
150 if (enter)
151 nmi_ts_start = time_get();
152 else
153 nmi_total_ts += time_get() - nmi_ts_start;
156 if (enter)
157 nmi_count++;
161 * get_sample - sample the CPU TSC and look for likely hardware latencies
163 * Used to repeatedly capture the CPU TSC (or similar), looking for potential
164 * hardware-induced latency. Called with interrupts disabled and with
165 * hwlat_data.lock held.
167 static int get_sample(void)
169 struct trace_array *tr = hwlat_trace;
170 time_type start, t1, t2, last_t2;
171 s64 diff, total, last_total = 0;
172 u64 sample = 0;
173 u64 thresh = tracing_thresh;
174 u64 outer_sample = 0;
175 int ret = -1;
177 do_div(thresh, NSEC_PER_USEC); /* modifies interval value */
179 nmi_cpu = smp_processor_id();
180 nmi_total_ts = 0;
181 nmi_count = 0;
182 /* Make sure NMIs see this first */
183 barrier();
185 trace_hwlat_callback_enabled = true;
187 init_time(last_t2, 0);
188 start = time_get(); /* start timestamp */
190 do {
192 t1 = time_get(); /* we'll look for a discontinuity */
193 t2 = time_get();
195 if (time_u64(last_t2)) {
196 /* Check the delta from outer loop (t2 to next t1) */
197 diff = time_to_us(time_sub(t1, last_t2));
198 /* This shouldn't happen */
199 if (diff < 0) {
200 pr_err(BANNER "time running backwards\n");
201 goto out;
203 if (diff > outer_sample)
204 outer_sample = diff;
206 last_t2 = t2;
208 total = time_to_us(time_sub(t2, start)); /* sample width */
210 /* Check for possible overflows */
211 if (total < last_total) {
212 pr_err("Time total overflowed\n");
213 break;
215 last_total = total;
217 /* This checks the inner loop (t1 to t2) */
218 diff = time_to_us(time_sub(t2, t1)); /* current diff */
220 /* This shouldn't happen */
221 if (diff < 0) {
222 pr_err(BANNER "time running backwards\n");
223 goto out;
226 if (diff > sample)
227 sample = diff; /* only want highest value */
229 } while (total <= hwlat_data.sample_width);
231 barrier(); /* finish the above in the view for NMIs */
232 trace_hwlat_callback_enabled = false;
233 barrier(); /* Make sure nmi_total_ts is no longer updated */
235 ret = 0;
237 /* If we exceed the threshold value, we have found a hardware latency */
238 if (sample > thresh || outer_sample > thresh) {
239 struct hwlat_sample s;
240 u64 latency;
242 ret = 1;
244 /* We read in microseconds */
245 if (nmi_total_ts)
246 do_div(nmi_total_ts, NSEC_PER_USEC);
248 hwlat_data.count++;
249 s.seqnum = hwlat_data.count;
250 s.duration = sample;
251 s.outer_duration = outer_sample;
252 ktime_get_real_ts64(&s.timestamp);
253 s.nmi_total_ts = nmi_total_ts;
254 s.nmi_count = nmi_count;
255 trace_hwlat_sample(&s);
257 latency = max(sample, outer_sample);
259 /* Keep a running maximum ever recorded hardware latency */
260 if (latency > tr->max_latency) {
261 tr->max_latency = latency;
262 latency_fsnotify(tr);
266 out:
267 return ret;
270 static struct cpumask save_cpumask;
271 static bool disable_migrate;
273 static void move_to_next_cpu(void)
275 struct cpumask *current_mask = &save_cpumask;
276 int next_cpu;
278 if (disable_migrate)
279 return;
281 * If for some reason the user modifies the CPU affinity
282 * of this thread, then stop migrating for the duration
283 * of the current test.
285 if (!cpumask_equal(current_mask, current->cpus_ptr))
286 goto disable;
288 get_online_cpus();
289 cpumask_and(current_mask, cpu_online_mask, tracing_buffer_mask);
290 next_cpu = cpumask_next(smp_processor_id(), current_mask);
291 put_online_cpus();
293 if (next_cpu >= nr_cpu_ids)
294 next_cpu = cpumask_first(current_mask);
296 if (next_cpu >= nr_cpu_ids) /* Shouldn't happen! */
297 goto disable;
299 cpumask_clear(current_mask);
300 cpumask_set_cpu(next_cpu, current_mask);
302 sched_setaffinity(0, current_mask);
303 return;
305 disable:
306 disable_migrate = true;
310 * kthread_fn - The CPU time sampling/hardware latency detection kernel thread
312 * Used to periodically sample the CPU TSC via a call to get_sample. We
313 * disable interrupts, which does (intentionally) introduce latency since we
314 * need to ensure nothing else might be running (and thus preempting).
315 * Obviously this should never be used in production environments.
317 * Executes one loop interaction on each CPU in tracing_cpumask sysfs file.
319 static int kthread_fn(void *data)
321 u64 interval;
323 while (!kthread_should_stop()) {
325 move_to_next_cpu();
327 local_irq_disable();
328 get_sample();
329 local_irq_enable();
331 mutex_lock(&hwlat_data.lock);
332 interval = hwlat_data.sample_window - hwlat_data.sample_width;
333 mutex_unlock(&hwlat_data.lock);
335 do_div(interval, USEC_PER_MSEC); /* modifies interval value */
337 /* Always sleep for at least 1ms */
338 if (interval < 1)
339 interval = 1;
341 if (msleep_interruptible(interval))
342 break;
345 return 0;
349 * start_kthread - Kick off the hardware latency sampling/detector kthread
351 * This starts the kernel thread that will sit and sample the CPU timestamp
352 * counter (TSC or similar) and look for potential hardware latencies.
354 static int start_kthread(struct trace_array *tr)
356 struct cpumask *current_mask = &save_cpumask;
357 struct task_struct *kthread;
358 int next_cpu;
360 if (WARN_ON(hwlat_kthread))
361 return 0;
363 /* Just pick the first CPU on first iteration */
364 current_mask = &save_cpumask;
365 get_online_cpus();
366 cpumask_and(current_mask, cpu_online_mask, tracing_buffer_mask);
367 put_online_cpus();
368 next_cpu = cpumask_first(current_mask);
370 kthread = kthread_create(kthread_fn, NULL, "hwlatd");
371 if (IS_ERR(kthread)) {
372 pr_err(BANNER "could not start sampling thread\n");
373 return -ENOMEM;
376 cpumask_clear(current_mask);
377 cpumask_set_cpu(next_cpu, current_mask);
378 sched_setaffinity(kthread->pid, current_mask);
380 hwlat_kthread = kthread;
381 wake_up_process(kthread);
383 return 0;
387 * stop_kthread - Inform the hardware latency samping/detector kthread to stop
389 * This kicks the running hardware latency sampling/detector kernel thread and
390 * tells it to stop sampling now. Use this on unload and at system shutdown.
392 static void stop_kthread(void)
394 if (!hwlat_kthread)
395 return;
396 kthread_stop(hwlat_kthread);
397 hwlat_kthread = NULL;
401 * hwlat_read - Wrapper read function for reading both window and width
402 * @filp: The active open file structure
403 * @ubuf: The userspace provided buffer to read value into
404 * @cnt: The maximum number of bytes to read
405 * @ppos: The current "file" position
407 * This function provides a generic read implementation for the global state
408 * "hwlat_data" structure filesystem entries.
410 static ssize_t hwlat_read(struct file *filp, char __user *ubuf,
411 size_t cnt, loff_t *ppos)
413 char buf[U64STR_SIZE];
414 u64 *entry = filp->private_data;
415 u64 val;
416 int len;
418 if (!entry)
419 return -EFAULT;
421 if (cnt > sizeof(buf))
422 cnt = sizeof(buf);
424 val = *entry;
426 len = snprintf(buf, sizeof(buf), "%llu\n", val);
428 return simple_read_from_buffer(ubuf, cnt, ppos, buf, len);
432 * hwlat_width_write - Write function for "width" entry
433 * @filp: The active open file structure
434 * @ubuf: The user buffer that contains the value to write
435 * @cnt: The maximum number of bytes to write to "file"
436 * @ppos: The current position in @file
438 * This function provides a write implementation for the "width" interface
439 * to the hardware latency detector. It can be used to configure
440 * for how many us of the total window us we will actively sample for any
441 * hardware-induced latency periods. Obviously, it is not possible to
442 * sample constantly and have the system respond to a sample reader, or,
443 * worse, without having the system appear to have gone out to lunch. It
444 * is enforced that width is less that the total window size.
446 static ssize_t
447 hwlat_width_write(struct file *filp, const char __user *ubuf,
448 size_t cnt, loff_t *ppos)
450 u64 val;
451 int err;
453 err = kstrtoull_from_user(ubuf, cnt, 10, &val);
454 if (err)
455 return err;
457 mutex_lock(&hwlat_data.lock);
458 if (val < hwlat_data.sample_window)
459 hwlat_data.sample_width = val;
460 else
461 err = -EINVAL;
462 mutex_unlock(&hwlat_data.lock);
464 if (err)
465 return err;
467 return cnt;
471 * hwlat_window_write - Write function for "window" entry
472 * @filp: The active open file structure
473 * @ubuf: The user buffer that contains the value to write
474 * @cnt: The maximum number of bytes to write to "file"
475 * @ppos: The current position in @file
477 * This function provides a write implementation for the "window" interface
478 * to the hardware latency detetector. The window is the total time
479 * in us that will be considered one sample period. Conceptually, windows
480 * occur back-to-back and contain a sample width period during which
481 * actual sampling occurs. Can be used to write a new total window size. It
482 * is enfoced that any value written must be greater than the sample width
483 * size, or an error results.
485 static ssize_t
486 hwlat_window_write(struct file *filp, const char __user *ubuf,
487 size_t cnt, loff_t *ppos)
489 u64 val;
490 int err;
492 err = kstrtoull_from_user(ubuf, cnt, 10, &val);
493 if (err)
494 return err;
496 mutex_lock(&hwlat_data.lock);
497 if (hwlat_data.sample_width < val)
498 hwlat_data.sample_window = val;
499 else
500 err = -EINVAL;
501 mutex_unlock(&hwlat_data.lock);
503 if (err)
504 return err;
506 return cnt;
509 static const struct file_operations width_fops = {
510 .open = tracing_open_generic,
511 .read = hwlat_read,
512 .write = hwlat_width_write,
515 static const struct file_operations window_fops = {
516 .open = tracing_open_generic,
517 .read = hwlat_read,
518 .write = hwlat_window_write,
522 * init_tracefs - A function to initialize the tracefs interface files
524 * This function creates entries in tracefs for "hwlat_detector".
525 * It creates the hwlat_detector directory in the tracing directory,
526 * and within that directory is the count, width and window files to
527 * change and view those values.
529 static int init_tracefs(void)
531 struct dentry *d_tracer;
532 struct dentry *top_dir;
534 d_tracer = tracing_init_dentry();
535 if (IS_ERR(d_tracer))
536 return -ENOMEM;
538 top_dir = tracefs_create_dir("hwlat_detector", d_tracer);
539 if (!top_dir)
540 return -ENOMEM;
542 hwlat_sample_window = tracefs_create_file("window", 0640,
543 top_dir,
544 &hwlat_data.sample_window,
545 &window_fops);
546 if (!hwlat_sample_window)
547 goto err;
549 hwlat_sample_width = tracefs_create_file("width", 0644,
550 top_dir,
551 &hwlat_data.sample_width,
552 &width_fops);
553 if (!hwlat_sample_width)
554 goto err;
556 return 0;
558 err:
559 tracefs_remove(top_dir);
560 return -ENOMEM;
563 static void hwlat_tracer_start(struct trace_array *tr)
565 int err;
567 err = start_kthread(tr);
568 if (err)
569 pr_err(BANNER "Cannot start hwlat kthread\n");
572 static void hwlat_tracer_stop(struct trace_array *tr)
574 stop_kthread();
577 static bool hwlat_busy;
579 static int hwlat_tracer_init(struct trace_array *tr)
581 /* Only allow one instance to enable this */
582 if (hwlat_busy)
583 return -EBUSY;
585 hwlat_trace = tr;
587 disable_migrate = false;
588 hwlat_data.count = 0;
589 tr->max_latency = 0;
590 save_tracing_thresh = tracing_thresh;
592 /* tracing_thresh is in nsecs, we speak in usecs */
593 if (!tracing_thresh)
594 tracing_thresh = last_tracing_thresh;
596 if (tracer_tracing_is_on(tr))
597 hwlat_tracer_start(tr);
599 hwlat_busy = true;
601 return 0;
604 static void hwlat_tracer_reset(struct trace_array *tr)
606 stop_kthread();
608 /* the tracing threshold is static between runs */
609 last_tracing_thresh = tracing_thresh;
611 tracing_thresh = save_tracing_thresh;
612 hwlat_busy = false;
615 static struct tracer hwlat_tracer __read_mostly =
617 .name = "hwlat",
618 .init = hwlat_tracer_init,
619 .reset = hwlat_tracer_reset,
620 .start = hwlat_tracer_start,
621 .stop = hwlat_tracer_stop,
622 .allow_instances = true,
625 __init static int init_hwlat_tracer(void)
627 int ret;
629 mutex_init(&hwlat_data.lock);
631 ret = register_tracer(&hwlat_tracer);
632 if (ret)
633 return ret;
635 init_tracefs();
637 return 0;
639 late_initcall(init_hwlat_tracer);