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Linux/kernel/time/timer_stats.c

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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 <tglx@timesys.com>
  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 <d.pensator@gmail.com>
 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  */
 53 struct 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         u32                     flags;
 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  */
 84 static DEFINE_RAW_SPINLOCK(table_lock);
 85 
 86 /*
 87  * Per-CPU lookup locks for fast hash lookup:
 88  */
 89 static DEFINE_PER_CPU(raw_spinlock_t, tstats_lookup_lock);
 90 
 91 /*
 92  * Mutex to serialize state changes with show-stats activities:
 93  */
 94 static DEFINE_MUTEX(show_mutex);
 95 
 96 /*
 97  * Collection status, active/inactive:
 98  */
 99 int __read_mostly timer_stats_active;
100 
101 /*
102  * Beginning/end timestamps of measurement:
103  */
104 static 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 
116 static unsigned long nr_entries;
117 static struct entry entries[MAX_ENTRIES];
118 
119 static 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 
136 static struct entry *tstat_hash_table[TSTAT_HASH_SIZE] __read_mostly;
137 
138 static 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 
146 static struct entry *alloc_entry(void)
147 {
148         if (nr_entries >= MAX_ENTRIES)
149                 return NULL;
150 
151         return entries + nr_entries++;
152 }
153 
154 static 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  */
167 static 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  * @tflags:     The flags field of the timer
231  *
232  * When the timer is already registered, then the event counter is
233  * incremented. Otherwise the timer is registered in a free slot.
234  */
235 void timer_stats_update_stats(void *timer, pid_t pid, void *startf,
236                               void *timerf, char *comm, u32 tflags)
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.flags = tflags;
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 
270 static 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 
280 static 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->flags & TIMER_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  */
345 static 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 
359 static 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 '':
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 
395 static int tstats_open(struct inode *inode, struct file *filp)
396 {
397         return single_open(filp, tstats_show, NULL);
398 }
399 
400 static 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 
408 void __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 
416 static 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);
426 

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