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1/*
2 * kernel/time/timer_stats.c
3 *
4 * Collect timer usage statistics.
5 *
6 * Copyright(C) 2006, Red Hat, Inc., Ingo Molnar
7 * Copyright(C) 2006 Timesys Corp., Thomas Gleixner <[email protected]>
8 *
9 * timer_stats is based on timer_top, a similar functionality which was part of
10 * Con Kolivas dyntick patch set. It was developed by Daniel Petrini at the
11 * Instituto Nokia de Tecnologia - INdT - Manaus. timer_top's design was based
12 * on dynamic allocation of the statistics entries and linear search based
13 * lookup combined with a global lock, rather than the static array, hash
14 * and per-CPU locking which is used by timer_stats. It was written for the
15 * pre hrtimer kernel code and therefore did not take hrtimers into account.
16 * Nevertheless it provided the base for the timer_stats implementation and
17 * was a helpful source of inspiration. Kudos to Daniel and the Nokia folks
18 * for this effort.
19 *
20 * timer_top.c is
21 * Copyright (C) 2005 Instituto Nokia de Tecnologia - INdT - Manaus
22 * Written by Daniel Petrini <[email protected]>
23 * timer_top.c was released under the GNU General Public License version 2
24 *
25 * We export the addresses and counting of timer functions being called,
26 * the pid and cmdline from the owner process if applicable.
27 *
28 * Start/stop data collection:
29 * # echo [1|0] >/proc/timer_stats
30 *
31 * Display the information collected so far:
32 * # cat /proc/timer_stats
33 *
34 * This program is free software; you can redistribute it and/or modify
35 * it under the terms of the GNU General Public License version 2 as
36 * published by the Free Software Foundation.
37 */
38
39#include <linux/proc_fs.h>
40#include <linux/module.h>
41#include <linux/spinlock.h>
42#include <linux/sched.h>
43#include <linux/seq_file.h>
44#include <linux/kallsyms.h>
45
46#include <asm/uaccess.h>
47
48/*
49 * This is our basic unit of interest: a timer expiry event identified
50 * by the timer, its start/expire functions and the PID of the task that
51 * started the timer. We count the number of times an event happens:
52 */
53struct entry {
54 /*
55 * Hash list:
56 */
57 struct entry *next;
58
59 /*
60 * Hash keys:
61 */
62 void *timer;
63 void *start_func;
64 void *expire_func;
65 pid_t pid;
66
67 /*
68 * Number of timeout events:
69 */
70 unsigned long count;
71 unsigned int timer_flag;
72
73 /*
74 * We save the command-line string to preserve
75 * this information past task exit:
76 */
77 char comm[TASK_COMM_LEN + 1];
78
79} ____cacheline_aligned_in_smp;
80
81/*
82 * Spinlock protecting the tables - not taken during lookup:
83 */
84static DEFINE_RAW_SPINLOCK(table_lock);
85
86/*
87 * Per-CPU lookup locks for fast hash lookup:
88 */
89static DEFINE_PER_CPU(raw_spinlock_t, tstats_lookup_lock);
90
91/*
92 * Mutex to serialize state changes with show-stats activities:
93 */
94static DEFINE_MUTEX(show_mutex);
95
96/*
97 * Collection status, active/inactive:
98 */
99int __read_mostly timer_stats_active;
100
101/*
102 * Beginning/end timestamps of measurement:
103 */
104static ktime_t time_start, time_stop;
105
106/*
107 * tstat entry structs only get allocated while collection is
108 * active and never freed during that time - this simplifies
109 * things quite a bit.
110 *
111 * They get freed when a new collection period is started.
112 */
113#define MAX_ENTRIES_BITS 10
114#define MAX_ENTRIES (1UL << MAX_ENTRIES_BITS)
115
116static unsigned long nr_entries;
117static struct entry entries[MAX_ENTRIES];
118
119static atomic_t overflow_count;
120
121/*
122 * The entries are in a hash-table, for fast lookup:
123 */
124#define TSTAT_HASH_BITS (MAX_ENTRIES_BITS - 1)
125#define TSTAT_HASH_SIZE (1UL << TSTAT_HASH_BITS)
126#define TSTAT_HASH_MASK (TSTAT_HASH_SIZE - 1)
127
128#define __tstat_hashfn(entry) \
129 (((unsigned long)(entry)->timer ^ \
130 (unsigned long)(entry)->start_func ^ \
131 (unsigned long)(entry)->expire_func ^ \
132 (unsigned long)(entry)->pid ) & TSTAT_HASH_MASK)
133
134#define tstat_hashentry(entry) (tstat_hash_table + __tstat_hashfn(entry))
135
136static struct entry *tstat_hash_table[TSTAT_HASH_SIZE] __read_mostly;
137
138static void reset_entries(void)
139{
140 nr_entries = 0;
141 memset(entries, 0, sizeof(entries));
142 memset(tstat_hash_table, 0, sizeof(tstat_hash_table));
143 atomic_set(&overflow_count, 0);
144}
145
146static struct entry *alloc_entry(void)
147{
148 if (nr_entries >= MAX_ENTRIES)
149 return NULL;
150
151 return entries + nr_entries++;
152}
153
154static int match_entries(struct entry *entry1, struct entry *entry2)
155{
156 return entry1->timer == entry2->timer &&
157 entry1->start_func == entry2->start_func &&
158 entry1->expire_func == entry2->expire_func &&
159 entry1->pid == entry2->pid;
160}
161
162/*
163 * Look up whether an entry matching this item is present
164 * in the hash already. Must be called with irqs off and the
165 * lookup lock held:
166 */
167static struct entry *tstat_lookup(struct entry *entry, char *comm)
168{
169 struct entry **head, *curr, *prev;
170
171 head = tstat_hashentry(entry);
172 curr = *head;
173
174 /*
175 * The fastpath is when the entry is already hashed,
176 * we do this with the lookup lock held, but with the
177 * table lock not held:
178 */
179 while (curr) {
180 if (match_entries(curr, entry))
181 return curr;
182
183 curr = curr->next;
184 }
185 /*
186 * Slowpath: allocate, set up and link a new hash entry:
187 */
188 prev = NULL;
189 curr = *head;
190
191 raw_spin_lock(&table_lock);
192 /*
193 * Make sure we have not raced with another CPU:
194 */
195 while (curr) {
196 if (match_entries(curr, entry))
197 goto out_unlock;
198
199 prev = curr;
200 curr = curr->next;
201 }
202
203 curr = alloc_entry();
204 if (curr) {
205 *curr = *entry;
206 curr->count = 0;
207 curr->next = NULL;
208 memcpy(curr->comm, comm, TASK_COMM_LEN);
209
210 smp_mb(); /* Ensure that curr is initialized before insert */
211
212 if (prev)
213 prev->next = curr;
214 else
215 *head = curr;
216 }
217 out_unlock:
218 raw_spin_unlock(&table_lock);
219
220 return curr;
221}
222
223/**
224 * timer_stats_update_stats - Update the statistics for a timer.
225 * @timer: pointer to either a timer_list or a hrtimer
226 * @pid: the pid of the task which set up the timer
227 * @startf: pointer to the function which did the timer setup
228 * @timerf: pointer to the timer callback function of the timer
229 * @comm: name of the process which set up the timer
230 *
231 * When the timer is already registered, then the event counter is
232 * incremented. Otherwise the timer is registered in a free slot.
233 */
234void timer_stats_update_stats(void *timer, pid_t pid, void *startf,
235 void *timerf, char *comm,
236 unsigned int timer_flag)
237{
238 /*
239 * It doesn't matter which lock we take:
240 */
241 raw_spinlock_t *lock;
242 struct entry *entry, input;
243 unsigned long flags;
244
245 if (likely(!timer_stats_active))
246 return;
247
248 lock = &per_cpu(tstats_lookup_lock, raw_smp_processor_id());
249
250 input.timer = timer;
251 input.start_func = startf;
252 input.expire_func = timerf;
253 input.pid = pid;
254 input.timer_flag = timer_flag;
255
256 raw_spin_lock_irqsave(lock, flags);
257 if (!timer_stats_active)
258 goto out_unlock;
259
260 entry = tstat_lookup(&input, comm);
261 if (likely(entry))
262 entry->count++;
263 else
264 atomic_inc(&overflow_count);
265
266 out_unlock:
267 raw_spin_unlock_irqrestore(lock, flags);
268}
269
270static void print_name_offset(struct seq_file *m, unsigned long addr)
271{
272 char symname[KSYM_NAME_LEN];
273
274 if (lookup_symbol_name(addr, symname) < 0)
275 seq_printf(m, "<%p>", (void *)addr);
276 else
277 seq_printf(m, "%s", symname);
278}
279
280static int tstats_show(struct seq_file *m, void *v)
281{
282 struct timespec period;
283 struct entry *entry;
284 unsigned long ms;
285 long events = 0;
286 ktime_t time;
287 int i;
288
289 mutex_lock(&show_mutex);
290 /*
291 * If still active then calculate up to now:
292 */
293 if (timer_stats_active)
294 time_stop = ktime_get();
295
296 time = ktime_sub(time_stop, time_start);
297
298 period = ktime_to_timespec(time);
299 ms = period.tv_nsec / 1000000;
300
301 seq_puts(m, "Timer Stats Version: v0.3\n");
302 seq_printf(m, "Sample period: %ld.%03ld s\n", period.tv_sec, ms);
303 if (atomic_read(&overflow_count))
304 seq_printf(m, "Overflow: %d entries\n", atomic_read(&overflow_count));
305 seq_printf(m, "Collection: %s\n", timer_stats_active ? "active" : "inactive");
306
307 for (i = 0; i < nr_entries; i++) {
308 entry = entries + i;
309 if (entry->timer_flag & TIMER_STATS_FLAG_DEFERRABLE) {
310 seq_printf(m, "%4luD, %5d %-16s ",
311 entry->count, entry->pid, entry->comm);
312 } else {
313 seq_printf(m, " %4lu, %5d %-16s ",
314 entry->count, entry->pid, entry->comm);
315 }
316
317 print_name_offset(m, (unsigned long)entry->start_func);
318 seq_puts(m, " (");
319 print_name_offset(m, (unsigned long)entry->expire_func);
320 seq_puts(m, ")\n");
321
322 events += entry->count;
323 }
324
325 ms += period.tv_sec * 1000;
326 if (!ms)
327 ms = 1;
328
329 if (events && period.tv_sec)
330 seq_printf(m, "%ld total events, %ld.%03ld events/sec\n",
331 events, events * 1000 / ms,
332 (events * 1000000 / ms) % 1000);
333 else
334 seq_printf(m, "%ld total events\n", events);
335
336 mutex_unlock(&show_mutex);
337
338 return 0;
339}
340
341/*
342 * After a state change, make sure all concurrent lookup/update
343 * activities have stopped:
344 */
345static void sync_access(void)
346{
347 unsigned long flags;
348 int cpu;
349
350 for_each_online_cpu(cpu) {
351 raw_spinlock_t *lock = &per_cpu(tstats_lookup_lock, cpu);
352
353 raw_spin_lock_irqsave(lock, flags);
354 /* nothing */
355 raw_spin_unlock_irqrestore(lock, flags);
356 }
357}
358
359static ssize_t tstats_write(struct file *file, const char __user *buf,
360 size_t count, loff_t *offs)
361{
362 char ctl[2];
363
364 if (count != 2 || *offs)
365 return -EINVAL;
366
367 if (copy_from_user(ctl, buf, count))
368 return -EFAULT;
369
370 mutex_lock(&show_mutex);
371 switch (ctl[0]) {
372 case '0':
373 if (timer_stats_active) {
374 timer_stats_active = 0;
375 time_stop = ktime_get();
376 sync_access();
377 }
378 break;
379 case '1':
380 if (!timer_stats_active) {
381 reset_entries();
382 time_start = ktime_get();
383 smp_mb();
384 timer_stats_active = 1;
385 }
386 break;
387 default:
388 count = -EINVAL;
389 }
390 mutex_unlock(&show_mutex);
391
392 return count;
393}
394
395static int tstats_open(struct inode *inode, struct file *filp)
396{
397 return single_open(filp, tstats_show, NULL);
398}
399
400static const struct file_operations tstats_fops = {
401 .open = tstats_open,
402 .read = seq_read,
403 .write = tstats_write,
404 .llseek = seq_lseek,
405 .release = single_release,
406};
407
408void __init init_timer_stats(void)
409{
410 int cpu;
411
412 for_each_possible_cpu(cpu)
413 raw_spin_lock_init(&per_cpu(tstats_lookup_lock, cpu));
414}
415
416static int __init init_tstats_procfs(void)
417{
418 struct proc_dir_entry *pe;
419
420 pe = proc_create("timer_stats", 0644, NULL, &tstats_fops);
421 if (!pe)
422 return -ENOMEM;
423 return 0;
424}
425__initcall(init_tstats_procfs);